1. Left-to-Right Shunting
A. General Considerations
Cardiac septation occurs between the third and sixth weeks of fetal development. The septum primum, which arises from the roof of the common atrium and descends inferiorly, initially divides the common atrium. The ostium primum is the opening below the inferior edge of the septum primum, which is obliterated as the septum primum fuses with the endocardial cushions. The ostium secundum forms in the midportion of the septum primum prior to closure of the ostium primum. The septum secundum also arises from the roof of the atrium and descends along the right side of the septum primum and covers the ostium secundum. This creates a flap valve whereby blood from the inferior vena cava may preferentially stream beneath the edge of the septum secundum and through the ostium secundum into the left atrium. After birth, the increase in left atrial pressure usually closes this pathway.
An ASD is a hole in the atrial septum (Figure 19–31). ASDs are the third-most common congenital heart defect, occurring in 1 out of 1000 live births and representing 10% of congenital heart defects. The most common ASD is the secundum defect, which occurs when the ostium secundum is too large for complete coverage by the septum secundum. Ostium secundum defects account for about 80% of ASDs. An ostium primum ASD, representing 10% of ASDs, occurs as a result of failure of fusion of the septum primum with the endocardial cushions (ostium primum defect is discussed later in the section on Atrioventricular Septal Defects [AVSD]). A third type of ASD is the sinus venosus defect, seen in about 10% of cases. Sinus venosus ASDs are caused by abnormal fusion of the venous pathways with the atrium and are characterized by defects high in the atrial septum near the orifice of the superior vena cava or, less commonly, low in the atrial septum near the inferior vena cava. Sinus venosus defects are frequently associated with partial anomalous pulmonary venous connection, usually with the right upper pulmonary vein draining into the superior vena cava near the cavoatrial junction. The rarest type of ASD is the unroofed coronary sinus septal defect. This occurs when there is loss of the common wall between the coronary sinus and the left atrium adjacent to the atrial septum. This unroofing of the coronary sinus leads to a communication between the right and left atria at the site of the coronary sinus.
Sinus venosus and ostium secundum defects in the atrial septum as viewed from the opened right atrium.
Failure of postnatal fusion of the septum secundum to the septum primum results in a persistent slit-like communication known as a PFO. PFOs are extremely common in the general population, and autopsy studies have demonstrated a prevalence of 27%. PFOs are generally considered separate from other ASDs because of the absence of significant shunting, but they remain important clinically because of the occurrence of paradoxical embolization. A paradoxical embolus is usually a blood clot arising from a systemic vein, which would normally pass to the lungs, but in the presence of a septal defect may instead cross into the systemic circulation.
ASDs lead to increased pulmonary blood flow secondary to left-to-right shunting. Shunting at the atrial level is determined by the size of the defect and by the relative ventricular compliance (ie, blood preferentially fills the more compliant ventricle). At birth, both chambers are equally compliant, but as PVR falls, the right ventricle remodels and becomes more compliant. Shunting across the atrial septum causes a volume load on the right heart. A volume load is created by additional venous return to a chamber during diastole.
The volume overload from an ASD is usually well tolerated, and patients are frequently asymptomatic. Symptoms tend to develop when the ratio of pulmonary to systemic blood flow (Qp/Qs) exceeds two. The most common symptoms are fatigue, shortness of breath, exercise intolerance, and recurrent respiratory infections. Older patients with untreated ASDs tend to develop atrial dysrhythmias, and adults may develop congestive heart failure and RV dysfunction. Pulmonary vascular obstructive disease may develop rarely as a late complication of untreated ASD. Paradoxical embolization is also an important potential complication of ASD.
The classic physical findings in patients with ASDs include fixed splitting of the second heart sound and a systolic ejection murmur at the left upper sternal border due to increased flow across a normal pulmonary valve. A diastolic flow murmur across the tricuspid valve is occasionally audible. A prominent RV lift and increased intensity of the pulmonary component of the second heart sound may occur with pulmonary hypertension. Chest radiography shows cardiomegaly, with enlargement of the right atrium, right ventricle, and pulmonary artery. EKG frequently demonstrates right axis deviation and an incomplete right bundle branch block. When right bundle branch block occurs with a leftward or superior axis, the diagnosis of AVSD should be considered. Echocardiography confirms the diagnosis of ASD and defines the anatomy. Cardiac catheterization is important in selected cases to assess PVR in older patients, but it is used more frequently with therapeutic intent for device closure of ASDs.
Because of the long-term complications associated with ASD, repair is recommended for all patients with symptomatic defects and in asymptomatic patients in whom the Qp/Qs is greater than 1.5. Repair is usually performed in children prior to school age. Closure of ASDs may be performed surgically or using a device deployed in the cardiac catheterization lab.
Surgical repair is usually recommended for large secundum defects and for most other types of ASDs. The heart is usually exposed by median sternotomy. Other surgical approaches have been proposed, including minimally invasive techniques, but there are technical drawbacks associated with each of the alternative approaches. In most cases, a limited midline incision with a partial lower sternal split provides adequate exposure and a cosmetically acceptable scar. The atrial septum is exposed through a right atriotomy. Small secundum defects or PFOs may sometimes be closed primarily by suturing the edge of the septum primum to the edge of the septum secundum. More commonly, larger defects are closed using a patch (polytetrafluoroethylene or autologous pericardium) and a running polypropylene suture. When anomalous pulmonary venous drainage is present, a baffle is created to redirect the flow across the ASD. In all cases, care is taken to deair the left atrium to avoid the complication of air embolization.
The first transcatheter device closure of an ASD was performed in 1976. A number of devices are currently available for percutaneous closure of a secundum ASD, and success rates for device deployment are greater than 90%. Device closure has the advantages of fewer complications and a shorter hospitalization. Device closure of small to moderate secundum ASDs and PFOs has now become the standard of care at most large centers.
Occasionally, adults will present with a newly diagnosed ASD. Many studies have confirmed that ASD closure in adults over the age of 40 increases survival and limits the development of heart failure. When the Qp/Qs is less than 1.5 and the ratio of pulmonary to systemic vascular resistance (Rp/Rs) is greater than 0.7, significant pulmonary vascular obstructive disease is usually present. A PVR in excess of 10-12 Woods units·m2 represents a contraindication to ASD closure.
Operative mortality for ASD repair is close to 0%. Atrial arrhythmias (1.2%) and postpericardiotomy syndrome (4.7%) are the most common postoperative complications. The long-term survival for patients undergoing ASD repair in childhood is normal. The major long-term complication following surgical closure of ASD is the development of supraventricular arrhythmias, although the risk is lowered when the ASD is closed in childhood. The persistence of this risk despite relief of right-sided volume overload is thought to be related to incomplete atrial remodeling or due to the presence of the atriotomy scar. Longer follow-up is required to determine whether device closure alters the risk of atrial dysrhythmias.
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et al.: Evolving surgical strategy for sinus venosus atrial septal defect: effect on sinus node function and late venous obstruction. Ann Thorac Surg 2007;84:1651–1655.
Ventricular Septal Defect
A. General Considerations
Ventricular septation is a complex process that requires accurate development and alignment of a number of structures including the muscular interventricular septum, the AV septum (arising from the endocardial cushions), and the infundibular septum (which divides the outflow tracts of the right and left ventricles). The membranous septum is a fibrous portion of the ventricular septum, which is adjacent to the central fibrous body (where the mitral, tricuspid, and aortic valve annuli make contact).
VSDs are the most common congenital heart anomalies (with the exception of bicuspid aortic valve, which occurs in about 1.3% of the population). VSDs are present in about 4 of 1000 live births and represent about 40% of congenital heart defects. VSDs are classified based on their location in the ventricular septum (Figure 19–32). The most common defects are perimembranous (80%), which are located in the area of the membranous septum. Inlet defects (5%) are located beneath the septal leaflet of the tricuspid valve and are sometimes called atrioventricular (AV) canal-type defects. Defects located high in the ventricular septum are outlet defects (10%). Outlet VSDs are typically adjacent to both the pulmonary and aortic valves. Outlet defects are also known by several other names, including supracristal, infundibular, or doubly committed subarterial. Outlet defects are more common in the Asian population. Muscular (or trabecular) VSDs (5%) are completely bordered by muscle. Muscular VSDs are frequently multiple and may be associated with perimembranous or outlet defects. The size of VSDs varies. By definition, a VSD is nonrestrictive when its size (or the cumulative size of multiple defects) is greater than or equal to the size of the aortic annulus.
Anatomic locations of various ventricular septal defects. The wall of the right ventricle has been excised to expose the ventricular septum.
A VSD causes increased pulmonary blood flow due to left-to-right shunting primarily during systole. This creates a volume load on the left heart (the left atrium and ventricle receive the increased venous return during diastole). The right ventricle is not volume loaded (blood is ejected from the left ventricle through the VSD and directly into the pulmonary circulation), but it does experience a pressure load. The volume of shunt flow is determined by the size of the defect and by the ratio of Rp/Rs. After birth, the PVR is still high, and shunting across a VSD is sometimes minimal. Over the first several weeks of life, shunting tends to increase as the PVR normally falls. Therefore, a patient with a large VSD may be asymptomatic at birth but eventually develop severe congestive heart failure.
The natural history for patients with isolated VSDs is highly variable. Most VSDs are restrictive and tend to close spontaneously during the first year of life. Large VSDs are nonrestrictive, resulting in RV and pulmonary pressures that are systemic or nearly systemic, and high pulmonary blood flow with Qp/Qs ratios greater than 2.5-3. Moderate VSDs are restrictive, with pulmonary pressures that are one-half systemic (or less) and Qp/Qs ratios of 1.5-2.5. Small VSDs are highly restrictive; RV pressures remain normal, and the Qp/Qs is less than 1.5. Patients with large VSDs tend to develop symptoms of congestive heart failure by 2 months of age. Untreated, excessive pulmonary blood flow leads to pulmonary vascular obstructive disease by the second year of life. Patients with smaller VSDs may remain asymptomatic. In patients with outlet VSDs, prolapse of the aortic valve may occur, producing aortic insufficiency.
Signs of heart failure in infants with large VSDs include tachypnea, hepatomegaly, poor feeding, and failure to thrive. On physical examination, there is a pansystolic murmur at the left sternal border. Usually, the murmur is louder with smaller defects. The precordium is active. The pulmonary component of the second heart sound is accentuated in the presence of pulmonary hypertension. Chest radiography shows increased pulmonary vascular markings and cardiomegaly. EKG is significant for RV hypertrophy.
Patients with small VSDs have little shunting and are usually asymptomatic, having only a pansystolic murmur. Patients with moderate VSDs manifest symptoms and signs proportional to the degree of shunting.
In patients who have developed significant pulmonary vascular obstructive disease, the volume of left-to-right shunting is decreased, and the murmur may disappear. Eisenmenger physiology results when the shunt flow reverses to right-to-left, creating cyanosis.
The diagnosis of VSD is confirmed by echocardiography, which accurately defines the anatomy and excludes the presence of associated defects. Cardiac catheterization is used selectively in older children and adults in whom elevated PVR is suspected. Pulmonary vascular resistance is calculated by the following formula:
where PAmean is the mean pulmonary artery pressure and LA is the left atrial pressure. The units of resistance by this formulation (using pressures in millimeters of mercury and pulmonary flow in liters per minute) are Woods units (which can be expressed in dynes·sec/cm5 by multiplying by 80). PVR may be fixed or reactive, and at the time of cardiac catheterization, response to various pulmonary vasodilators may be assessed.
The management of a patient with a VSD depends on the size of the defect, the type of the defect, the shunt volume, and the PVR. In general, patients with large defects who have intractable congestive heart failure or failure to thrive should undergo early surgical repair. If the congestive symptoms can be moderated by medical therapy, then surgery may be deferred until 6 months of age. Patients with moderate VSDs may be safely followed. If closure has not occurred by school age, then surgical closure is indicated. Small VSDs with Qp/Qs of less than 1.5 do not require closure. There is a small long-term risk of endocarditis for these patients, but this can be minimized with the appropriate use of prophylactic antibiotics. Patients with outlet VSDs have a significant risk of developing aortic insufficiency due to leaflet prolapse, and, therefore, all of these patients should undergo surgical closure. Older children and adults must undergo catheterization to assess the pulmonary circulation. When there is a fixed PVR greater than 8-10 Woods units·m2, then surgery is contraindicated.
Exposure of the ventricular septum is most often achieved by making a right atriotomy and retracting the leaflets of the tricuspid valve. This provides access to perimembranous, inlet, and most trabecular VSDs. Outlet VSDs are frequently best exposed via a pulmonary arteriotomy because the defect lies just beneath the valve. Muscular VSDs located near the ventricular apex can be very difficult to expose, and an apical ventriculotomy may be necessary. Once the defect is exposed, it is closed using a polytetrafluoroethylene patch and a running polypropylene suture, although some centers may prefer other patch material or interrupted suture technique. It is important to understand the anatomy of the conduction tissue when closing VSDs. The AV node is an atrial structure that lies at the apex of an anatomic triangle (known as the triangle of Koch) formed by the coronary sinus, the tendon of Todaro (a prominent band leading from the inferior vena cava and inserting in the atrial septum), and the septal attachment of the tricuspid valve. The node then gives rise to the bundle of His, which penetrates the AV junction beneath the membranous septum. The bundle of His then bifurcates into right and left bundle branches, which pass along either side of the muscular ventricular septum. In the presence of a perimembranous VSD, the bundle of His passes along the posterior and inferior rim of the defect, generally on the left ventricular side. In this critical area, sutures must be placed superficially on the RV side a few millimeters from the edge of the defect. The bundle of His tends to run along the posterior and inferior margin of inlet VSDs as well. The conduction tissue is usually remote from outlet and trabecular VSDs.
Pulmonary artery banding is a palliative maneuver used to protect the pulmonary circulation from excessive blood flow. Pulmonary artery banding is currently performed only in patients who are felt to be poor candidates for VSD closure because of either associated illness or anatomic complexity, such as multiple muscular VSDs (“Swiss cheese” septum). A band is placed around the main pulmonary artery and tightened to achieve a distal pulmonary artery pressure of about one-half systemic. The band is secured to the adventitia of the pulmonary artery to prevent its migration. Distal migration may result in narrowing and poor growth of one or both branch pulmonary arteries, while proximal migration can cause deformity of the pulmonary valve. Later, when the patient is a candidate for VSD closure, the band must be removed. Repair of the main pulmonary artery at the band site is usually necessary and can typically be accomplished by scar resection and primary closure or patch repair.
Transcatheter devices allow closure of some VSDs in the cardiac catheterization lab. For specific VSDs, such as muscular, device closure may be preferable. Complications with device closure include complete heart block (3.8%), device embolization (0.01%), and aortic insufficiency (0.03%). For simple perimembranous VSDs, the risk of device closure is in excess of traditional surgical closure.
Surgical closure of a VSD is associated with a mortality of less than 1%. Potential complications include injury to the conduction tissue and injury to the tricuspid or aortic valves. Transient heart block may result from tissue swelling or injury from retraction, but permanent heart block occurs in less than 2% of cases. When heart block develops after surgery, patients are usually observed for a period of 7-10 days prior to permanent pacemaker implantation. Tricuspid insufficiency may be precipitated by annular distortion or chordal restriction by the VSD patch or sutures. The aortic valve may also be injured by inaccurate suturing (especially in perimembranous and outlet defects). A residual VSD is seen in about 5% of cases, and reoperation is indicated when significant shunting persists (Qp/Qs > 1.5) or the residual defect is larger than 2 mm in size. The Qp/Qs ratio can be calculated by measuring oxygen saturations and using the following formula derived from the Fick equation:
Qp/Qs = (Ao – SVC)/(PV − PA)
where Ao is the aortic (or systemic) saturation, SVC is the saturation in the superior vena cava, PV is the saturation in the pulmonary veins (which is usually estimated to be 95%-100%), and PA is the saturation in the pulmonary arteries. Intraoperative echocardiography is used routinely to identify residual defects, which can then be repaired before the patient leaves the operating room.
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et al.: Results of transcatheter closure of perimembranous ventricular septal defect. Am J Cardiol 2010;106:1034–1037.
Atrioventricular Septal Defect
A. General Considerations
AVSDs represent a group of congenital abnormalities bound by a variable deficiency of the atrioventricular septum immediately above and below the AV valves. Other terms commonly applied to an AVSD include AV canal defects, endocardial cushion defects, and atrioventricular communis. Complete AVSDs have a single common AV valve orifice resulting in a single five-leaflet valve overlying both the right and left ventricles. Incomplete AVSDs have two separate AV valve orifices (tricuspid and mitral) with the mitral valve invariably having a cleft in the anterior leaflet. While most incomplete AVSDs have no ventricular level shunting, the classification of AVSDs as complete and incomplete depends only on the valve anatomy, not on the presence or absence of a VSD. Incomplete defects without associated ventricular level shunting have also been termed ostium primum ASDs, while those with a VSD have been described as intermediate or transitional AVSDs. AVSDs represent approximately 4% of congenital cardiac anomalies and are frequently associated with other cardiac malformations. AVSDs comprise 30%-40% of the cardiac abnormalities seen in patients with Down syndrome.
A complete AVSD is characterized by a common atrioventricular orifice, rather than separate mitral and tricuspid orifices, and a deficiency of endocardial cushion tissue, which results in an ASD and an inlet type of VSD (Figure 19–33). AVSDs were subclassified by Rastelli into the following three types according to the morphology of the anterior leaflet of the common AV valve:
Type A: The anterior bridging leaflet is divided and attached to the septum by multiple chordae.
Type B: The anterior bridging leaflet is attached to a papillary muscle in the right ventricle.
Type C: The anterior bridging leaflet is free-floating with no attachments except to the valve annulus.
Complete atrioventricular canal. The most common type has a divided anterior bridging leaflet. Both the left and right valvular components are attached to the interventricular septum with long, nonfused chordae. The left and right components of the posterior bridging leaflet are not separated.
When both left and right AV valves equally share the common AV valve orifice, the AVSD is termed balanced. Occasionally, the orifice may favor the right AV valve (right dominance) or the left AV valve (left dominance). In marked right dominance, the left AV valve and left ventricle are hypoplastic and frequently coexist with other left-sided abnormalities, including aortic stenosis, hypoplasia of the aorta, and coarctation. Conversely, marked left dominance results in a deficient right AV valve with associated hypoplasia of the right ventricle, pulmonary stenosis or atresia, and TOF. Patients with severe imbalance require staged single-ventricle reconstruction.
The conduction tissue is displaced in an ASVD and is at risk during the surgical repair. The AV node is located posteriorly and inferiorly of its normal position toward the coronary sinus in the triangle of Koch. This triangle is bounded by the coronary sinus, the posterior attachment of the inferior bridging leaflet, and the rim of the ASD. The bundle of His courses posteriorly and inferiorly to run along the leftward aspect of the crest of the VSD, giving off the left bundle branch and continuing as the right bundle branch.
Cardiac anomalies associated with AVSDs include: PDA (10%) and TOF (10%). Important abnormalities of the left AV valve include single papillary muscle (parachute mitral valve) (2%-6%) and double orifice mitral valve (8%-14%). A persistent left superior vena cava with or without an unroofed coronary sinus is encountered in 3% of patients with an AVSD. Double-outlet right ventricle (2%) significantly complicates or may even preclude complete surgical correction. As mentioned previously, left ventricular outflow tract obstruction from subaortic stenosis or redundant AV valve tissue occurs in 4%-7%.
The predominant hemodynamic features of an AVSD are the result of left-to-right shunting at the atrial and ventricular levels. In the absence of ventricular level shunting, the hemodynamics and clinical presentation of a patient with an incomplete AVSD resemble that of a typical secundum ASD with right atrial and RV volume overload. Patients with a complete AVSD with both atrial-level and ventricular-level shunting generally present early in infancy with signs and symptoms of congestive heart failure. In addition, moderate or severe left AV valve regurgitation occurs in approximately 10% of patients with an AVSD worsening the clinical picture. On physical examination, the precordium is hyperactive, often with a prominent thrill. Auscultatory findings include a systolic murmur along the left sternal border, a high-pitched murmur at the apex from the left AV valve regurgitation, and a middiastolic flow murmur across the common A-V valve. In the presence of elevated PVR, there may be a split first heart sound. Significant cardiomegaly and pulmonary overcirculation are found on the CXR. Electrocardiogram reveals biventricular hypertrophy, atrial enlargement, prolonged PR interval, leftward axis, and counterclockwise frontal plane loop. Echocardiography is diagnostic, defining the atrial and ventricular level shunting, valvular anatomy, and any associated anomalies. Up to 90% of untreated individuals with a complete AVSD develop pulmonary vascular disease by 1 year of age due to the large left-to-right shunt, potentially exacerbated by the associated AV valve regurgitation. Patients with trisomy 21 tend to develop pulmonary vascular obstructive disease earlier than chromosomally normal infants due to small airway disease, chronic hypoventilation, and elevated Pco2. Initial aggressive medical management is undertaken to relieve the symptoms of congestive heart failure. Elective surgical correction should be performed by age 3-6 months. Earlier intervention is indicated for failure of medical management.
Cardiac catheterization should be performed for patients over the age of 1 year, for patients with signs or symptoms of increased PVR, or in some cases to further evaluate other associated major cardiac anomalies. If the PVR is high, it is important to remeasure it while the child is breathing 100% oxygen with and without nitric oxide. If the pulmonary resistance falls, it implies that much of the elevated resistance is dynamic and can be managed in the perioperative period by ventilatory manipulation, supplemental oxygen, and nitric oxide. More recently, sildenafil has been shown to decrease elevation in PVR in children with congenital heart disease. Markedly elevated PVR (> 10 Woods units·m2) that does not respond to oxygen administration is generally considered a contraindication to repair.
Operative treatment is almost always necessary as soon as symptoms are observed to prevent further clinical deterioration. Even in the absence of symptoms, operation is best performed before 6 months of age. Pulmonary artery banding, which permits delaying the repair until the child is larger, is no longer used today except in select complex or single-ventricle cases, extremely low birth weight or prematurity, and very poor clinical condition. This approach exposes the child to the risks of two operations, and the overall mortality exceeds that of primary repair in infancy. Patients with incomplete AVSDs usually require repair within the first few years of life.
Two techniques are widely employed for the repair of complete AVSDs: a 1-patch technique and a 2-patch technique. Incomplete AVSDs are repaired with the single-patch technique. Regardless of which approach is selected, the goals are to close the ASD and VSD and to separate the common AV valve into two nonstenotic, competent valves. The cleft in the anterior leaflet of the mitral valve is generally closed to lessen the risk of long-term mitral regurgitation. For the 2-patch technique, separate patches are used for the ASD and VSD. For the 1-patch technique, the superior and inferior bridging leaflets are divided along a line separating them into right and left components. A single patch is utilized to close both the ventricular and ASDs. The cut edges of the leaflets are then resuspended to the patch. For defects with a small VSD component, a modified single-patch technique may be employed. For this method, a single patch is sewn directly to the rim of the VSD, sandwiching the bridging leaflets between the patch and the crest of the VSD.
The short-term and long-term success of the operation is highly dependent on the status of the PVR and the surgeon’s ability to maintain competence of the mitral valve. In developed countries, it is fortunately relatively uncommon for patients to present late in with an AVSD and refractory PVR elevations. Although earlier reports recommend that the cleft in the left AV valve should not be closed and the valve should be treated as a trileaflet structure, most authors now believe that closure of the cleft is an important mechanism in preventing postoperative left AV valve regurgitation. Significant AV valve regurgitation at the conclusion of surgery, severe dysplasia of the left AV valve, and failure to close the cleft of the left AV valve have been identified as important risk factors for reoperation. Significant postoperative left AV valve regurgitation is also a risk factor for operative and long-term mortality. The cleft should not be completely closed in the presence of a single papillary muscle to avoid causing the left AV valve stenosis. In the case of a double-orifice valve, the bridging tissue should not be divided to create a single opening in the valve.
Operative mortality is related largely to associated cardiac anomalies and left AV valve regurgitation. Mortality for repair of uncomplicated incomplete AVSDs is 0%-1.6%, while the addition of left AV valve regurgitation increases mortality to 4%-6%. For complete AVSDs, the mortality without left AV valve regurgitation is approximately 4%-5%, compared with 13% when significant degrees of regurgitation are present. The difference in operative mortality between patients with and without regurgitation underscores the importance of careful management of the left AV valve.
The majority of reoperations after repair of AVSD are due to left AV valve regurgitation or the development of subaortic stenosis. Significant postoperative AV valve regurgitation occurs in 6%-26% of patients, necessitating reoperation for valve repair or replacement in 3%-12%. The incidence of permanent complete heart block is approximately 1%-2%. Heart block encountered in the immediate postoperative period may be transient due to edema of or trauma to the AV node or bundle of His. However, right bundle branch block is common (22%).
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A. General Considerations
The ductus arteriosus is a normal fetal vascular structure that allows blood from the right ventricle to bypass the high-resistance pulmonary vascular bed and pass directly to the systemic circulation. The ductus communicates between the main pulmonary artery (or proximal left pulmonary artery) and the proximal descending thoracic aorta. Histologically, the media of the ductus contains a predominance of smooth muscle cells, while the media of the aorta and pulmonary artery contain well-developed elastic fibers. Vasocontrol of the ductus is mediated by two important mechanisms: oxygen tension and prostaglandin levels. During fetal development, low oxygen tension and high levels of circulating prostaglandin maintain ductal patency. During the final trimester, the ductus becomes less sensitive to prostaglandins and more sensitive to the effects of oxygen tension. Following birth, the rise in oxygen tension and fall in prostaglandins (which were previously supplied principally by the placenta) lead to ductal closure, which is usually complete by 12-24 hours. After closure, the ductus becomes a fibrous cord known as the ligamentum arteriosum. Failure of closure of the ductus leads to the condition called patent ductus arteriosus (PDA) which occurs in about 1 out of 1200 live births and accounts for 7% of congenital heart defect. The incidence is much higher in premature infants (> 20%). This elevated incidence is thought to be related to immaturity of the ductal wall resulting in impaired sensitivity to oxygen tension.
PDA may occur as an isolated defect, or it may occur in association with a number of other anomalies. Patency of the ductus arteriosus is desirable in a number of defects in which there is either inadequate pulmonary blood flow (such as pulmonary atresia) or inadequate systemic blood flow (as in severe coarctation of the aorta). The discovery that extrinsic delivery of prostaglandins can maintain ductal patency has played a critical role in improving the survival of these patients.
The physiologic manifestation of PDA is shunting of blood across the ductus. The shunt volume is determined by the size of the ductus and by the ratio of pulmonary to systemic vascular resistance. At birth, the PVR drops dramatically and continues to decline over the first several weeks of life. As a result, shunting across a PDA is from left-to-right. Excessive pulmonary blood flow can lead to congestive heart failure. In extreme cases, hypotension and systemic malperfusion may result. Patients with a large PDA who survive infancy tend to develop pulmonary vascular obstructive disease. Eisenmenger physiology results when the PVR exceeds the systemic vascular resistance, producing a reversal of shunting across the ductus to right-to-left. This leads to cyanosis and, eventually, RV failure. Small PDAs may persist to adulthood without producing any symptoms or physiologic derangement. Endocarditis and endarteritis have been reported as long-term complications of PDA.
In patients with PDA, symptoms are proportional to the shunt volume and the presence of associated defects. Left-to-right shunting produces volume overload of the left heart. Infants with congestive heart failure demonstrate symptoms of tachypnea, tachycardia, and poor feeding. Older children may present with recurrent respiratory infections, fatigue, and failure to thrive. Physical findings include a widened pulse pressure and a continuous “machinery” murmur heard best along the left upper sternal border. Chest radiography shows increased pulmonary vascular markings and left heart enlargement. Left ventricular hypertrophy and left atrial enlargement may be evident on the electrocardiogram. Echocardiography is the diagnostic method of choice. Diagnostic cardiac catheterization is performed only in older patients with suspected pulmonary hypertension to evaluate for pulmonary vascular obstructive disease. More frequently, catheterization is utilized for transcatheter occlusion of the ductus.
PDA closure is performed for all symptomatic patients. Closure is also recommended for asymptomatic patients due to the risk of heart failure, pulmonary hypertension, and endocarditis. Closure of the ductus may be accomplished by one of three approaches: pharmacologic, surgical, and endovascular. Indomethacin, which is a prostaglandin inhibitor, stimulates PDA closure in premature infants. It is rarely effective in full-term infants. The dosing regimen is 0.1-0.2 mg/kg intravenously at 12- or 24-hour intervals for a total of three doses. This is effective in about 80% of premature babies. Due to its side effects, indomethacin is contraindicated in patients with sepsis, renal insufficiency, intracranial hemorrhage, or bleeding disorders. Failure of indomethacin after two complete courses results in referral for surgical closure.
The surgical approach to PDA is through a left posterolateral thoracotomy via the third or fourth intercostal space. The pleura is incised over the proximal descending thoracic aorta, which allows medial retraction of the vagus nerve. The recurrent laryngeal nerve curves behind the ductus and should be protected throughout the procedure. Dissection is then performed to demonstrate the pertinent anatomy. In many cases, the ductus is the largest vascular structure present, and it must not be confused with the aorta. Ductal tissue is extremely friable, so direct manipulation is minimized. In premature infants, the ductus is controlled with a single surgical clip; this procedure is commonly performed in the neonatal intensive care unit, thereby avoiding problems associated with patient transfer. In older patients, occlusion of the ductus is achieved with simple silk ligature or, preferably, by division between ligatures to minimize recurrence.
Recently, thoracoscopic techniques have been developed to perform PDA ligation. This approach has the potential benefits of decreased pain and quicker recovery. Disadvantages include a substantial learning curve and increased operating time.
A number of endovascular devices have been developed for the purpose of transcatheter occlusion of the PDA. This approach is very successful in older infants, children, and adults with small and moderate sized PDAs and has become the treatment of choice at many centers. Surgical therapy is reserved for PDAs having a large diameter or very short length.
Rarely, an adult will present with a significant PDA. These patients must be carefully evaluated for the presence of pulmonary vascular obstructive disease prior to ductal closure. If the patient is not a candidate for device closure, surgical closure can be problematic. Calcification of the ductal wall is common in adults, which makes ligation hazardous. In some cases, cardiopulmonary bypass may be required with patch closure of the ductus from within the pulmonary artery.
Closure of the ductus by surgical or transcatheter techniques is achieved with a mortality that approaches zero. Potential complications include pneumothorax, recurrent laryngeal nerve injury, and chylothorax (from injury to the thoracic duct). Long-term survival should be normal following PDA ligation in most patients. Survival in premature infants depends primarily on the extent of prematurity with its attendant complications.
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A. General Considerations
Isolated pulmonary stenosis occurs in 5%-8% of all congenital cardiac anomalies. The pulmonary valve is usually trileaflet with fusion of the commissures. The valve can appear thickened and domed on echocardiography. Most patients have an associated PFO or a secundum ASD. Pulmonary stenosis may be valvar or subvalvar due to muscular narrowing of the infundibulum (Figure 19–34).
Pulmonary stenosis. A: Valvular pulmonary stenosis. B: Infundibular pulmonary stenosis.
Young infants with severe pulmonary stenosis present with failure to thrive, right heart failure, and possibly hypoxic spells. Older children tend to have mild to moderate stenosis that is asymptomatic. They may, however, complain of shortness of breath with exertion or arrhythmias. The murmur of pulmonary stenosis tends to be prominent and therefore is not missed on routine examination. The presence of a systolic ejection murmur should prompt further workup, including an echocardiogram, which is diagnostic. Patients may be followed symptomatically with mild to moderate pulmonary stenosis. Surgical or catheter-based intervention should be considered for a gradient higher than 50 mm Hg, progressive ventricular hypertrophy, or new tricuspid regurgitation.
Neonates presenting with profound cyanosis from severe pulmonary stenosis need to be placed on PGE1 to maintain ductal patency. The ductus will maintain adequate pulmonary blood flow so that the patient can be stabilized. For isolated pulmonary stenosis, balloon valvuloplasty by an interventional cardiologist is highly successful and has replaced surgical intervention for the majority of patients. Asymptomatic infants with systemic RV pressures from pulmonary stenosis are also excellent candidates for balloon dilation. Surgical valvotomy or a transannular patch for pulmonary stenosis is reserved for patients who have failed balloon dilation, who have a severely hypoplastic valve annulus, or who have other associated anomalies including muscular infundibular narrowing. Older patients with progressive isolated pulmonary stenosis are excellent candidates for elective balloon dilation when they develop elevated RV pressures.
Early mortality for patients with critical pulmonary stenosis is 3%-10%. Restenosis occurs in 10%-25% of patients. Once the outflow obstruction is relieved, the RV hypertrophy and tricuspid insufficiency regress. Although overall survival is excellent for isolated pulmonary stenosis, over 50% of patients will require additional interventions, including repeat balloon dilation, pulmonary valve replacement, and ASD closure. Late atrial and ventricular arrhythmias occur in 38% of patients. Twenty-five year survival is 90%-96%.
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et al.: Long-term outcome after treatment of isolated pulmonary valve stenosis. Int J Cardiol 2012;156:11–15.
A. General Considerations
Ebstein’s malformation was first described by Wilhelm Ebstein in 1866 as a constellation of clinical findings resulting from an abnormality of the tricuspid valve. It has become evident over time that the malformation is a disease of the entire right ventricle and the development of the tricuspid valve. It involves a spectrum of anatomical abnormalities of variable severity, which include apical displacement of the septal and mural leaflets of the tricuspid valve, which have failed to delaminate from the underlying myocardium; thinning or atrialization of the inlet component of the right ventricle, with variable dilation; and malformation of the anterosuperior leaflet, with anomalous attachments, redundancy, and fenestrations. Several other cardiac anomalies are often associated with the RV changes, such as atrial and VSDs, obstruction of the RV outlet, and Wolff–Parkinson–White syndrome. Ebstein’s malformation can also afflict the left-sided systemic AV valve in the setting of congenitally corrected transposition.
The malformation is rare, accounting for no more than 1% of all congenital cardiac anomalies. Due to the significant anatomic variability in the abnormalities of the tricuspid valve and right ventricle, the age at presentation and severity of symptoms can also be highly variable. Patients who present in infancy have the poorest prognosis. There is a high rate of fetal death, hydrops, and pulmonary hypoplasia when the diagnosis is made during fetal life. Cyanosis is the most common presentation in infancy. These patients have severe tricuspid regurgitation with a poorly functioning right ventricle in the face of elevated pulmonary arterial resistance. The result is a state of low cardiac output dependent on right-to-left shunting across the fossa ovalis.
With less severe derangements of the tricuspid valve and preserved ventricular function, patients tend to present later in adolescence or early adulthood. Many patients are asymptomatic and present with a murmur noted on physical examination. In symptomatic patients, a common presentation involves the new onset of atrial arrhythmias or reentrant tachycardia. Exercise tolerance may be diminished, with cyanosis during extreme exertion if an ASD is present. Those patients with an intact atrial septum will often progress to congestive heart failure with increasing cardiomegaly.
Echocardiography is usually sufficient for accurate diagnosis and anatomic evaluation. The degree of displacement, tethering, and dysplasia of the valvar leaflets, as well as the amount of regurgitation, can be determined. Ventricular function and the extent of atrialization of the right ventricle can also be evaluated. Additional abnormalities, including the presence and direction of a shunt at the atrial level, can be assessed. Electrocardiographic findings include incomplete right bundle branch block, right axis deviation, ventricular preexcitation, and atrial arrhythmias. The CXR can vary from normal, in patients with mild anatomic abnormalities, to the classic “wall-to-wall” heart. Cardiac catheterization is rarely necessary.
As noted previously, neonates often present with profound cyanosis and may require prostaglandins to maintain adequate flow of blood to the lungs during the early neonatal period when pulmonary resistance is high. It is important to distinguish functional from anatomic pulmonary atresia. In patients with functional atresia, it may be possible to wean them from the infusion of prostaglandins while maintaining adequate saturations of oxygen as pulmonary resistance falls. These patients can then be followed for development of further symptoms.
In neonates who cannot be weaned from prostaglandins due to unacceptable levels of hypoxemia, or in those with anatomic pulmonary atresia, it is necessary to construct a systemic-to-pulmonary shunt to maintain adequate pulmonary blood flow. For neonates who also develop significant symptoms of congestive heart failure while on prostaglandin, it is necessary to address the underlying valvar pathology. The options include closure of the tricuspid valve, with or without fenestration, along with construction of a modified Blalock-Taussig shunt, repair of the tricuspid valve if ventricular function is reasonable, or cardiac transplantation.
In the older patient with progressive symptoms, a variety of surgical options exist to address the malformed tricuspid valve. Most are based on techniques designed to mobilize the leading edge of the anterosuperior leaflet, aiming to create a competent monocusp valve with or without plication of the atrialized portion of the right ventricle. There is ongoing debate as to the necessity of obliterating the atrialized portion of the right ventricle. Historically, plication of this portion of the ventricle has been an integral part of most repairs, albeit that no clear physiologic benefit with regards to improved ventricular function has been demonstrated. In addition, the potential exists for injury to the right coronary artery as a result of the plication, which may adversely impact late outcomes and contribute to ventricular arrhythmias.
Replacement of the tricuspid valve is a final option. The late survival free from reoperation, however, has been equivalent to valvar repair. If replacement is required, heterografts are preferred over mechanical valves due to risks of thrombosis. Other options using tissue valves include the insertion of pulmonary autografts, mitral valve homografts, and “top hat” mounted pulmonary or aortic homografts. When replacing the valve, the sutures should be brought around the coronary sinus, leaving it to drain into the right ventricle so as to minimize potential injury to the AV node. An open antiarrhythmia procedure is frequently performed concomitantly.
Ebstein’s malformation is a rare but challenging congenital cardiac defect. The high degree of anatomic variability makes it difficult to have a standardized approach to these children. The symptomatic neonate carries a very grave prognosis. The presence of associated cardiac and other congenital anomalies often make survival impossible. Surgical options are limited at this age and often still result in a poor outcome. Medical management, if possible, is the best, as surgical success improves with age. If surgery is required, conversion to functional tricuspid atresia often offers the best survival, as the ventricle in the severely symptomatic neonate functions poorly. Transplantation remains an option, but the availability of organs limits its utility.
Patients who are not symptomatic in the neonatal period will often remain free from symptoms well into adolescence. Electrophysiologic symptoms usually precede symptoms of congestive heart failure. Indications for repair at these ages include symptoms, cyanosis, and progressive cardiomegaly.
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A. General Considerations
Aortic stenosis is a form of left ventricular outflow tract obstruction that may occur at a valvar (70%), subvalvar (25%), or supravalvar (5%) level. Aortic stenosis occurs in about 4% of patients with congenital heart disease. The severity of aortic stenosis may be graded as mild (peak pressure gradient < 50 mm Hg), moderate (50 to 75 mm Hg), or severe (> 75 mm Hg).
Valvar aortic stenosis occurs secondary to maldevelopment of the aortic valve. Most commonly, a bicuspid valve is present, although tricuspid and unicuspid valves are also represented. In valvar aortic stenosis, the leaflets are thickened and frequently dysmorphic, and there is a variable degree of leaflet fusion along the commissures. The aortic annulus may be hypoplastic. In 20% of cases, valvar aortic stenosis is associated with other cardiac defects, most commonly coarctation of the aorta, PDA, VSD, or mitral stenosis. Men with valvar aortic stenosis outnumber women by a ratio of 4:1. There is a wide spectrum of clinical presentations of valvar aortic stenosis, but patients tend to present in one of two groups. Neonates and infants with severe aortic stenosis develop symptoms of rapidly progressive congestive heart failure, while older children generally have less severe obstruction and a more slowly progressive course.
Subvalvar aortic stenosis occurs below the level of the aortic valve and may be discrete (80%) or diffuse (20%). Discrete (or membranous) subaortic stenosis is rarely seen in infants and tends to progress over time. This lesion consists of a crescent or circumferential fibrous or fibromuscular membrane that protrudes into the left ventricular outflow tract. The pathogenesis of discrete subaortic stenosis is unknown, but it is thought to be an acquired lesion that develops secondary to a congenital abnormality of the left ventricular outflow tract in which abnormal flow patterns lead to endocardial injury with resultant fibrosis. Although the aortic valve leaflets are usually normal in discrete subaortic stenosis, the turbulent flow created by the obstruction can cause leaflet thickening and progressive aortic insufficiency. Diffuse subaortic stenosis is a more severe form of stenosis that creates a long, tunnel-like obstruction. Diffuse subaortic stenosis should be distinguished from hypertrophic cardiomyopathy. Both forms of subaortic stenosis are associated with a high risk of endocarditis.
Supravalvar aortic stenosis is characterized by thickening of the wall of the ascending aorta. The lesion may be localized (80%) to the region of the sinotubular ridge (at the level of the valve commissures), creating an hourglass deformity, or it may be more diffuse (20%), extending into the aortic arch and its branches. In both varieties, the aortic valve leaflets may be abnormal. The free edges of the aortic valve leaflets may adhere to the aortic wall in the region of intraluminal thickening, and this may lead to reduced coronary blood flow during diastole. Aortic wall thickening may also extend into the coronary ostia and further impair coronary blood flow. Associated cardiac lesions are common, particularly branch pulmonary artery stenoses. A genetic basis for supravalvar aortic stenosis has been established. About 50% of cases of supravalvar aortic stenosis are associated with Williams syndrome, in which a partial deletion of chromosome 7 (including the elastin gene) leads to the triad of supravalvar stenosis, mental retardation, and a characteristic “elfin” facies. Isolated mutations in the elastin gene have also been shown to produce familial supravalvar aortic stenosis with an autosomal dominant pattern of transmission. There is a significant incidence of endocarditis in patients with supravalvar aortic stenosis. Sudden death is frequently reported and is probably related to coronary obstruction.
Severe aortic stenosis is usually well-tolerated during fetal development. Although left ventricular output and antegrade flow across the aortic valve are decreased, the right ventricle compensates with increased output, and systemic perfusion is maintained by flow across the ductus. After birth, there is increased venous return to the left heart, and this exacerbates the pressure load created by the stenotic aortic valve, leading to left ventricular dysfunction. As the ductus closes during postnatal life, systemic malperfusion may develop with resulting hypotension, acidosis, and oliguria. Coronary perfusion is also impaired due to the combination of systemic hypotension and elevated left ventricular end-diastolic pressures. Patients with critical aortic stenosis typically exhibit severe left ventricular dysfunction. These patients usually show signs of distress soon after birth. On examination, there is impaired distal perfusion with poor capillary refill and diminished, thready pulses. A systolic ejection murmur may be absent if the cardiac output is severely diminished. Differential cyanosis may be observed due to perfusion of the lower body with desaturated blood shunting through the ductus. The electrocardiogram shows left ventricular hypertrophy, and the CXR displays cardiomegaly and pulmonary congestion. Echocardiography establishes the diagnosis.
In contrast to infants with critical aortic stenosis, older children with valvar aortic stenosis usually present with less severe stenosis (mild or moderate), and most are asymptomatic. Symptoms of angina, syncope, and congestive heart failure are not commonly reported. Congenital valvar aortic stenosis is a progressive lesion, however, and survival is dependent on the severity of stenosis and its rate of progression. Sudden cardiac death is the most common cause of mortality. Endocarditis occurs in less than 1% of patients. The diagnosis of valvar aortic stenosis in older children can frequently be made on physical examination. There is a classic systolic crescendo-decrescendo murmur at the upper sternal border, which radiates to the neck. An ejection click is often present. A visible apical impulse is suggestive of significant left ventricular hypertrophy. In severe cases, the pulse may be weak and delayed (pulsus tardus et parvus). The electrocardiogram shows left ventricular hypertrophy. The CXR is usually normal. Echocardiography accurately defines the level of stenosis and its severity. Using Doppler techniques, the pressure gradient across the stenotic valve may be estimated using a simplified form of the Bernoulli equation P = 4V2, where P is the pressure gradient and V is the peak flow velocity. Cardiac catheterization is generally reserved for therapeutic intervention.
The clinical findings in subvalvar aortic stenosis are similar to those for valvar stenosis. The signs and symptoms of supravalvar aortic stenosis are similar to those in other forms of left ventricular outflow tract obstruction. The diagnosis is made by echocardiography, but cardiac catheterization or cardiac MRI is essential to define the aortic, coronary, and pulmonary arterial anatomy prior to surgical intervention.
The neonate or infant with critical aortic stenosis represents a true emergency. Endotracheal intubation and inotropic support is routine. Ductal patency is maintained with prostaglandins, and acidosis is corrected. All patients with critical aortic stenosis require some form of urgent intervention. The approach is determined by the valve morphology and by the presence of associated defects. In its most extreme form, critical aortic stenosis may be associated with underdeveloped left-sided cardiac chambers and therefore may represent a form of HLHS. In these cases, single-ventricle palliation must be undertaken. For patients with adequate left-sided chambers, relief of aortic stenosis may be achieved by one of the following three approaches: percutaneous balloon valvuloplasty, surgical valvotomy, or aortic valve replacement. Balloon valvuloplasty is generally considered the procedure of choice when the aortic valve annulus is adequate and there are no associated cardiac defects. Alternatively, surgical valvotomy may be accomplished by closed or open techniques. The closed approach is performed using cardiopulmonary bypass without aortic cross-clamping. Dilators of increasing size are passed through a ventriculotomy in the left ventricular apex and advanced across the aortic valve. Some centers prefer open surgical valvotomy, which allows a precise valvotomy under direct vision, although aortic cross-clamping with cardioplegia is necessary. In all cases, the goal of therapy is to relieve stenosis without creating excessive aortic insufficiency. Dramatic clinical improvement is expected following balloon or surgical valve valvotomy, and early survivals of greater than 80% have been reported. The incidence of aortic insufficiency is slightly higher following balloon valvotomy. In most cases, however, stenosis will recur and repeat valvotomy or aortic valve replacement will eventually be required. Aortic valve replacement is problematic in the neonate due to small patient size. In these cases, many consider the best valve replacement to be a pulmonary autograft (Ross procedure) with enlargement of the aortic annulus (Konno aortoventriculoplasty). The Ross–Konno procedure has been used successfully for neonates with critical aortic stenosis in whom the aortic annulus is hypoplastic and for selected patients in whom valvuloplasty was unsuccessful. Survival following the Ross-Konno procedure in infants has been shown to be excellent. Growth of the pulmonary autograft has been documented, thereby making it an ideal valve replacement for children. Unfortunately, as part of the Ross procedure, the pulmonary valve must be replaced using a cryopreserved homograft, which does not grow, and homograft replacement must be anticipated at intervals as the patient grows.
All patients with severe valvar aortic stenosis should undergo intervention, as should all symptomatic patients with moderate stenosis. Asymptomatic patients with mild or moderate stenosis are generally observed. As described for critical aortic stenosis, the techniques used to relieve aortic stenosis in older patients include percutaneous balloon valvuloplasty, surgical valvulotomy, and valve replacement. Balloon valvuloplasty is usually performed as the primary intervention and is associated with a success rate of nearly 90% and a mortality of less than 1%. Open surgical valvotomy is an alternative approach with similar results. For valves that are severely dysplastic, develop restenosis after intervention, or become insufficient as a result of prior intervention, valve replacement may be necessary. For older children, there are more options for valve replacement. The choices include mechanical prostheses, bioprosthetic valves, and tissue substitutes, such as porcine xenografts, cryopreserved human allografts, and pulmonary autografts (Ross procedure). The mechanical valves are the most durable but require chronic anticoagulation. The bioprosthetic and tissue valves do not require long-term anticoagulation but tend to deteriorate over time (with the exception of the pulmonary autograft). The pulmonary autograft has the potential advantage of growth but the homograft used to replace the pulmonary valve will require replacement. Selection of the appropriate replacement valve is a complex decision requiring input from all involved parties.
Intervention for discrete subvalvar stenosis is usually undertaken when the gradient exceeds 30-50 mm Hg or when aortic insufficiency is present. In these patients, resection of the membrane is readily performed by a transaortic approach. In order to reduce the incidence of restenosis, many centers advocate concurrent performance of a septal myomectomy to alter the geometry of the left ventricular outflow tract.
When diffuse subaortic stenosis is associated with hypoplasia of the aortic annulus, repair is best achieved with a Konno aortoventriculoplasty, whereby an incision is carried across the aortic annulus and subjacent ventricular septum, the opening patched, and an aortic valve implanted. Patients with an adequate aortic annulus may undergo a septoplasty (modified Konno), in which the septal incision is confined to the immediate subvalvar area and a patch is used to widen the left ventricular outflow tract without replacing the aortic valve.
Operative intervention is indicated for patients with supravalvar aortic stenosis in whom the gradient exceeds 50 mm Hg. A number of operations have been proposed for the treatment of localized supravalvar stenosis. The classical repair involves a longitudinal incision across the obstruction in the ascending aorta, which is extended into the noncoronary sinus. The thickened, hypertrophic ridge is resected by endarterectomy, and the aortotomy is augmented with an elliptical patch. A variation of this repair involves creation of an inverted-Y aortotomy with one limb of the Y extended into the noncoronary sinus and the other into the right coronary sinus. A Y-shaped patch is then used to augment the aortotomy. Finally, the Brom repair is performed by transection of the ascending aorta beyond the supravalvar ridge. Separate incisions are then made through the supravalvar ridge into each sinus of Valsalva. Triangular patches are placed to augment each of these incisions, thereby relieving the supravalvar obstruction. Reconnection of the aortic root to the ascending aorta completes the repair. The repair of the diffuse type of supravalvar stenosis is performed under circulatory arrest with extensive patching of the ascending aorta, transverse arch, and involved arch arteries. Branch pulmonary stenoses are best managed using transcatheter techniques.
Operative mortality approaches zero for resection of discrete subaortic stenosis. The recurrence rate of discrete stenosis following membrane resection and myomectomy has been reported to be as low as 4%. Despite the technical complexity of repair of diffuse subaortic stenosis, excellent results have been reported with high survival and freedom from reoperation. The results of surgery for localized supravalvar aortic stenosis are generally good with low operative mortality and excellent long-term survival. The diffuse form is more difficult to treat, and recurrence is more likely. Overall results are much worse when severe bilateral pulmonary artery stenoses are present. The mortality for aortic valve replacement regardless of valve choice is 2%-5%. The need for reoperation is dependent on valve choice and patient size. Early and late ventricular arrhythmias may occur commonly in patients with significant left ventricular hypertrophy.
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A. General Considerations
Coarctation of the aorta is a narrowing of the proximal descending thoracic aorta distal to the origin of the left subclavian artery, near the insertion of the ductus arteriosus (or ligamentum arteriosum). The severity of luminal narrowing and the length of the aorta affected are variable. Coarctation is thought to occur as a result of ectopic tissue from the ductus arteriosus that migrates into the wall of the adjacent aorta. After birth, as the ductus closes, the ectopic tissue in the aorta also constricts. Frequently, a posterior shelf of tissue is present at the point of most severe obstruction. The aortic obstruction caused by coarctation creates a pressure load on the left ventricle.
The incidence of coarctation is about 0.5 per 1000 live births, and its prevalence is about 7% of congenital heart defects. Coarctation is commonly associated with other heart defects, including bicuspid aortic valve (in more than 50% of cases), PDA, and VSD. Other left-sided obstructive lesions may also be present, such as aortic arch hypoplasia, aortic stenosis, mitral stenosis, and left ventricular hypoplasia. Coarctation is also recognized to occur in association with Turner syndrome.
Patients with severe coarctation present in the newborn period. Aortic obstruction is so significant that perfusion of the lower body is dependent upon flow from the ductus arteriosus. Spontaneous ductal closure typically worsens the aortic obstruction and may lead to malperfusion of tissues distal to the coarctation. The pressure load on the left ventricle may precipitate congestive heart failure. Patients may develop shock with severe acidosis, oliguria, and diminished distal pulses. Infants with severe coarctation will generally not survive without intervention.
Older children with coarctation are usually asymptomatic. The diagnosis is commonly made on the basis of hypertension in the upper extremities with decreased pulses in the lower extremities. Noninvasive blood pressure measurements in all four extremities help to quantify the severity of aortic obstruction. Older patients tend to develop extensive collateral arteries that bypass the obstruction. Life expectancy for these patients is 34 years without operation typically due to the development of heart failure. Other long-term complications of coarctation include aortic dissection (21%), endocarditis (18%) (frequently involving a bicuspid aortic valve), intracranial hemorrhage (12%) (from Berry aneurysms, which occur more commonly in patients with coarctation), endarteritis (in the poststenotic area of the aorta at the site of the jet of turbulent flow), and aortic aneurysm.
The diagnosis of coarctation can usually be made clinically. The infant with significant coarctation is frequently asymptomatic at birth but following closure of the ductus develops signs of heart failure such as irritability, tachypnea, and poor feeding. Lower extremity pulses are absent, and upper extremity pulses may be weak. Chest radiography shows cardiomegaly and pulmonary venous congestion. There is a left ventricular strain pattern on the electrocardiogram. Echocardiography is usually diagnostic, demonstrating narrowing of the aorta at the coarctation site with a loss of pulsatility in the descending aorta.
In older children and adults with coarctation, a pressure gradient between the arms and legs usually can be demonstrated by measuring cuff pressures in all four extremities. On chest radiography, rib notching may be evident, secondary to erosion of the inferior rib borders from the development of large intercostal collateral vessels. Echocardiography usually confirms the diagnosis. Anatomic details may also be clarified with CTA and cMRI. Cardiac catheterization is usually not necessary.
Generally, all patients with coarctation should undergo surgical repair if the gradient is greater than 20 mm Hg. For neonates, the acute medical management includes initiation of PGE1 for the purpose of reopening the ductus; this maneuver partially relieves the aortic obstruction and augments perfusion of the lower body due to improved antegrade flow across the arch as well as right-to-left flow across the ductus. Prostaglandins are usually effective for reopening the ductus when initiated within 3-7 days of life but are less successful thereafter.
Surgical repair of coarctation is usually performed through a left posterolateral thoracotomy via the third or fourth intercostal space. The descending thoracic aorta, ductus (or ligamentum), transverse aortic arch, and brachiocephalic vessels are mobilized. Care is taken to preserve the vagus nerve and its recurrent laryngeal branch.
The coarctation is usually evident externally by narrowing or posterior indentation; however, the degree of internal narrowing is usually much more severe. A dose of heparin (100 units/kg) may be given intravenously for patients younger than 2 years. Proximal and distal control of the aorta is achieved using clamps. Usually, the proximal clamp is positioned on the transverse arch between the innominate and left carotid vessels with concomitant occlusion of the left carotid and left subclavian. In infants and children, the preferred surgical approach to coarctation is resection with extended end-to-end repair. A generous resection of the coarctation segment is performed. The proximal aorta is then spatulated along the lesser curvature and the distal aorta along the greater curvature. An extended end-to-end anastomosis is then performed.
In older children and adults, it may not be possible to perform a resection with primary repair without creating excessive tension on the anastomosis, which may lead to hemorrhage or scarring with recurrent coarctation. An alternative strategy is necessary in these cases. Patch aortoplasty may be performed in children in whom further growth is anticipated. The subclavian flap repair augments the narrowed aorta using native arterial tissue. Blood flow to the left arm is maintained by collateral vessels, although long-term studies have demonstrated a slight discrepancy in limb length in some patients. Prosthetic patch material may also be used. By avoiding circumferential prosthetic material, growth potential of the native aorta is preserved. The disadvantage of patch repair is a high risk of aneurysm formation. In adults, where growth is no longer an issue, resection of the coarctation may be performed with subsequent placement of a prosthetic interposition graft (either Dacron or polytetrafluoroethylene).
One of the principal concerns during coarctation repair is interruption of distal aortic blood flow, especially to the spinal cord. The anterior spinal artery is fed by major radicular branches from intercostal arteries. In patients without well-formed collaterals, ischemia of the spinal cord may be precipitated by aortic cross-clamping, and paraplegia may result. Protective measures include induction of mild hypothermia, maintenance of a high proximal aortic pressure, and minimization of cross-clamp time. In older patients, distal aortic perfusion may be maintained by the technique of left heart bypass, where oxygenated blood is taken from the left atrium and delivered to the femoral artery or distal aorta using a centrifugal pump. Overall, the incidence of paraplegia following coarctation repair is less than 1%.
Transcatheter therapy has been proposed for the primary therapy of coarctation, but this approach is controversial due to the incidence of recurrent coarctation, need for multiple interventions, injury to the femoral vasculature (for access), and aneurysm formation. Improved results have been achieved with balloon angioplasty with concurrent stent placement in older children and adults in whom further aortic growth is not anticipated. Balloon angioplasty is widely accepted for the treatment of recurrent coarctation following surgery, with 88%-94% achieving a gradient less than 20 mm Hg.
The early mortality following repair of coarctation in neonates is 1%-3%, while the risk in older children and adults is about 1%-2%. The incidence of recurrent coarctation following resection and end-to-end repair is about 10% whereas catheter-based interventions are associated with reintervention rates of 25% for balloon angioplasty and 5%-40% for stent placement. The long-term survival following repair of coarctation is determined by the presence of associated defects and the persistence of hypertension.
Following repair, patients may develop severe hypertension. This can be managed using intravenous beta-blockers (eg, esmolol) or vasodilators (eg, sodium nitroprusside). Uncontrolled hypertension can lead to the complication of mesenteric arteritis. Hypertension usually resolves within days to weeks after repair, although older children and adults may require lifelong antihypertensive therapy. Repair of coarctation during infancy is thought to minimize the risk of late hypertension.
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A. General Considerations
Vascular rings comprise a spectrum of vascular anomalies of the aortic arch, pulmonary artery, and brachiocephalic vessels. The clinically significant manifestation of these lesions is a varying degree of tracheoesophageal compression. These vascular anomalies can be divided into complete vascular rings and partial vascular rings. Complete vascular rings can be divided into double aortic arch and right aortic arch with left ligamentum arteriosum. These two categories can be further subdivided on the basis of the specific anatomy. Incomplete vascular rings include aberrant right subclavian artery, innominate artery compression, and pulmonary artery sling. Other rare variations, which have been described, include left aortic arch with right descending aorta and right ligamentum, and left aortic arch with aberrant right subclavian artery and right ligamentum. The incidence of clinically significant vascular rings is 1%-2% of all congenital heart defects.
Vascular rings and pulmonary slings have been described in conjunction with other cardiac defects, including, TOF, ASD, branch pulmonary artery stenosis, coarctation, AVSD, VSD, interrupted aortic arch, and aortopulmonary window. Significant associated cardiac anomalies occur in 11%-20% of patients with a vascular ring. A right aortic arch is generally associated with a greater incidence of coexisting anomalies.
By the end of the fourth week of embryonic development, the six aortic or branchial arches have formed between the dorsal aortae and ventral roots. Subsequent involution and migration of the arches results in the anatomically normal or abnormal development of the aorta and its branches. The majority of the first, second, and fifth arches regress. The third arch forms the common carotid artery and proximal internal carotid artery. The right fourth arch forms the proximal right subclavian artery. The left fourth arch contributes to the portion of the aortic arch from left carotid to left subclavian arteries. The proximal portion of the right sixth arch becomes the proximal portion of the right pulmonary artery, while the distal segment involutes. Similarly, the proximal left sixth arch contributes to the proximal left pulmonary artery, and the distal sixth arch becomes the ductus arteriosus.
The pulmonary artery is formed from two vascular precursors as well as through a combination of angiogenesis, the de novo development of new blood vessels, and vasculogenesis, the budding and migration of existing vessels. As stated previously, the proximal pulmonary arteries are based on the sixth arches, whereas the primitive lung buds initially derive their blood supply from the splanchnic plexus. Ultimately, these two segments of the pulmonary artery join to form the vascular network of the lung parenchyma.
Children with a complete vascular ring generally present within the first weeks to months of life. Typically, children with a double aortic arch present earlier in life than those with a right arch and retroesophageal left ligamentum. In the younger age group, respiratory symptoms predominate, as liquids are generally well tolerated. Respiratory symptoms may include stridor, nonproductive cough, apnea, or frequent respiratory infections. The cough is classically described as “seal bark,” or “brassy.” These symptoms may mimic asthma, respiratory infection, or reflux, and children with vascular rings are often initially misdiagnosed. With the transition to solid food, dysphagia becomes more apparent.
The presentation of a patient with an incomplete vascular ring is variable. Children with innominate artery compression usually present within the first 1-2 years of life with respiratory symptoms. Although, aberrant right subclavian artery is the most common arch abnormality, occurring in approximately 0.5%-1% of the population, it rarely causes symptoms. Classically, when symptoms do occur, they present in the seventh and eighth decade, as the aberrant vessel becomes ectatic and calcified, causing dysphagia lusoria due to impingement of the artery on the posterior esophagus. An aberrant right subclavian rarely causes symptoms except when it is of an abnormally large caliber or associated with tracheomalacia.
Children with pulmonary artery slings generally present with respiratory symptoms within the first few weeks to months of life. As with complete rings, respiratory symptoms may include stridor, nonproductive cough, apnea, or frequent respiratory infections and may mimic other conditions leading to misdiagnosis. Pulmonary artery slings are associated with complete tracheal rings in 30%-40% of patients, leading to focal or diffuse tracheal stenosis.
The methods for diagnosing a vascular ring are multiple because of the variability in presentation and the spectrum of diagnostic tests available. A child with a presumptive diagnosis of asthma or tracheomalacia may be referred to a pulmonologist and a diagnosis of vascular ring made or suspected initially by CXR and bronchoscopy. In some situations, the diagnosis is made by echocardiography during evaluation for concurrent cardiac defects. Regardless, the diagnosis generally begins with a CXR. Complementary studies may include barium esophagogram, CTa, cMRI, and bronchoscopy. Important modalities to define the tracheal anatomy in a patient with a pulmonary artery sling include CTA, cMRI, or bronchoscopy. Echocardiography may be diagnostic and may be used to rule out other cardiac anomalies. Tracheograms and cardiac catheterizations, which have been used extensively in the past, are rarely currently indicated.
A double aortic arch occurs when the distal portion of the right dorsal aorta fails to regress. The two arches form a complete ring, encircling the trachea and esophagus. The right arch is dominant in the majority of the cases, followed by left dominant, with codominant arches being the least common. The left and right carotid and subclavian arteries generally arise from their respective arches. The ligamentum arteriosum and descending aorta usually remain on the left.
The approach to repair of a double aortic arch is via a left posterolateral thoracotomy. The procedure can easily be accomplished through a limited, muscle-sparing incision through the third or fourth intercostal space. The pleura is incised, after identifying the vagus and phrenic nerves. The ligamentum or ductus arteriosum is divided while preserving the recurrent laryngeal nerve. The nondominant arch is then divided between two vascular clamps at the point where brachiocephalic flow is optimally preserved. If there is concern regarding the location for division, the arches can be temporarily occluded at various points while monitoring pulse and blood pressure in each limb. If there is an atretic segment, the division is done at the point of the atresia. Dissection around the esophagus and trachea in the region of the ligamentum/ductus and nondominant arch allows for retraction of the vascular structures and lysis of any residual obstructing adhesions.
There are three anatomic variations for a right arch with a left ligamentum, which cause a complete vascular ring. If the left fourth arch regresses between the aorta and left subclavian, a right aortic arch with aberrant left subclavian artery results. The ligamentum arteriosum is retroesophageal, bridging the left pulmonary artery and aberrant left subclavian, forming a complete vascular ring. If the left fourth arch regresses after the origin of the left subclavian artery but before the arch reaches the dorsal aorta to communicate with the left sixth arch (which becomes the ductus arteriosum), there is mirror-image branching. The ligamentum arteriosum arises directly from the descending aorta, or from a Kommerell diverticulum off of the descending aorta, forming the complete ring. If communication is maintained between the left fourth and sixth arches, there is mirror-image branching with the ligamentum arising from the anterior, mirror-image left subclavian, and a ring is not formed.
The surgical approach for a right aortic arch with retroesophageal left ligamentum arteriosum is the same as for a double arch. The ligamentum is divided, and any adhesions around the esophagus and trachea are lysed. Rarely, the Kommerell diverticulum has been reported to cause compression even after division of the ligamentum. As such, it may be prudent to resect or suspend the diverticulum posteriorly.
In innominate artery compression syndrome, the aortic arch and ligamentum are in their normal leftward position. However, the innominate artery arises partially or totally to the left of midline. As the artery courses from left to right anterior to the trachea, it causes tracheal compression. The symptoms of innominate artery compression may be mild to severe. With mild symptoms and minimal tracheal compression on bronchoscopy, children can be observed expectantly because the symptoms may resolve with growth. Indications for surgery include apnea, severe respiratory distress, significant stridor, or recurrent respiratory tract infection. Several approaches for the correction of innominate artery compression syndrome have been described. These include simple division, division with reimplantation into the right side of the ascending aorta, and suspension to the overlying sternum.
An aberrant right subclavian artery occurs when there is regression of the right fourth arch between the right common carotid and right subclavian arteries. The right subclavian then arises from the leftward descending aorta, laying posterior to the esophagus as it crosses from left to right. Although the artery can compress the esophagus posteriorly, it is rarely the cause of symptoms in children. Surgical treatment involves simple division via a left posterolateral thoracotomy. Rarely, reimplantation or grafting from the right carotid or aortic arch may be necessary.
Normally, the right and left sixth aortic arches contribute to the proximal portions of their respective pulmonary arteries. If the proximal left sixth arch involutes and the bud from the left lung migrates rightward to meet the right pulmonary artery, a pulmonary artery sling is formed. Pulmonary artery slings are associated with complete tracheal rings and tracheal stenosis in 30%-40% of patients. Origin of the right upper lobe bronchus from the trachea (“pig bronchus” or “bronchus suis”) has been reported in frequent association with pulmonary artery sling.
Initial attempts at the repair of a pulmonary artery sling involved reimplantation after division of the left pulmonary artery and translocation of the trachea without cardiopulmonary bypass. These early reports had a high incidence of left pulmonary artery thrombosis. This has led some authors to advocate division of the trachea and translocation of the left pulmonary artery. This approach would seem sensible if the trachea were being divided in the course of tracheal reconstruction. However, currently most authors advocate the reimplantation of the left pulmonary artery, which has resulted in excellent results. The procedure is done via a median sternotomy on cardiopulmonary bypass to insure optimal visualization of the repair. Aortic cross-clamping is not necessary. The left pulmonary artery is divided off of the right pulmonary artery, translocated anterior to the trachea, and reimplanted into the main pulmonary artery.
Any necessary reconstruction of the trachea for complete tracheal rings is done concurrently with bronchoscopic assistance. Many techniques for tracheal reconstruction have been described, with resection and primary reanastomosis and sliding tracheoplasty offering the most reliable results.
Over 95% of vascular rings without concurrent cardiac defects can be performed through a left thoracotomy. A right thoracotomy is indicated for the rare cases where there is a right ligamentum arteriosum. A right ligamentum occurs in the setting of a left aortic arch with right descending aorta, where the ligamentum bridges from the descending aorta to the right pulmonary artery forming a complete ring. Right ligamentum arteriosum has also been described with a left aortic arch with aberrant right subclavian artery. In this case, the ligamentum may arise from the aberrant subclavian artery, from a diverticulum off of the arch, or directly from the left arch to the right pulmonary artery. In addition, a double aortic arch with an atretic segment proximal to the right carotid artery is more easily divided through a right thoracotomy. The approach to these anomalies is the same as for a left-sided ring division, with the caveat that the right recurrent laryngeal nerve will loop around the right ligamentum.
Repair of vascular rings has been described using video-assisted thoracoscopic surgery (VATS) both with and without robotic assistance. Candidates for thoracoscopic division are limited to those patients requiring only the division of nonpatent vascular structures. In general, VATS is used for patients weighing more than15 kg due to current size limitations of the instruments.
Hospital mortality for the repair of a vascular ring was 1.6% in a recent series of 183 patients by Ruzmetov and colleagues. Overall survival was 96% at 35 years. Eight patients were repaired utilizing left pulmonary artery division and reimplantation for pulmonary artery sling, three of whom also required cardiopulmonary bypass for tracheal reconstruction. Of the 183 patients there were no operative mortalities and eight late deaths. All deaths were in patients with other complex cardiac anomalies. The major source of morbidity, as well as mortality, in this and other series is related to the tracheal reconstruction.
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A. General Considerations
Coronary artery anomalies occur in between 0.2% and 1.2% of the population. They can be classified as minor, secondary, or major on the basis of their clinical significance. Minor defects have no functional significance and are usually detected as incidental findings at cardiac catheterization. Secondary defects have no intrinsic significance but alter surgical management when they are present. An example of a secondary defect is an anomalous origin of the left anterior descending from the right coronary artery, which crosses the hypoplastic infundibulum in a patient with TOF. The presence of this vessel may prevent the safe performance of a transannular incision and thereby mandate the use of a conduit. Major defects are the most important form of coronary anomaly because they exert an intrinsically adverse effect on the myocardium. Major anomalies can be subdivided based on anatomy: coronary arteriovenous fistula, anomalous pulmonary origin of a coronary artery, anomalous aortic origin of a coronary artery, myocardial bridging, or coronary artery aneurysm.
Coronary arteriovenous fistula is the most common major coronary anomaly. An abnormal connection exists between a coronary artery (usually the right) and another vascular structure (usually one of the right heart chambers). Most fistulas are isolated and solitary. The fistula leads to left-to-right shunting, which can produce congestive heart failure. Other symptoms include angina, endocarditis, myocardial infarction, arrhythmia, and sudden death. The diagnosis is suggested by echocardiography and confirmed by catheterization.
The second-most common major coronary anomaly is the origin of a coronary artery from the pulmonary artery. The most common manifestation is the anomalous left coronary artery arising from the pulmonary artery (ALCAPA). The right coronary (or both coronaries) may also arise anomalously from the pulmonary artery but only in very rare cases. ALCAPA is usually well tolerated during fetal development, but after birth, the pulmonary systolic pressure usually drops (following ductal closure and decline in PVR) and the anomalous coronary is perfused with desaturated blood at low pressure. Collateral vessels develop between the normal right coronary artery and the abnormal left coronary, but the benefit is negated due to the development of coronary steal, whereby the collateral blood shunts left to right by retrograde flow in the anomalous coronary into the low-pressure pulmonary artery. Most patients will present between 6 weeks and 3 months of life. Typical symptoms include irritability, difficulty in feeding, and other signs of congestive heart failure. Untreated, ALCAPA is nearly always fatal. Rarely, patients will survive to adulthood and present with symptoms of angina or sudden death. On examination, patients with ALCAPA frequently have a holosystolic murmur of ischemic mitral regurgitation. The pulmonary component of the second heart sound may be pronounced because of pulmonary hypertension. Chest radiography is significant for cardiomegaly and pulmonary edema. Electrocardiographic evidence of ischemia and infarction is usually present. Echocardiography is usually diagnostic and is useful for assessing the severity of left ventricular dysfunction and ischemic mitral regurgitation that are commonly present. Catheterization is occasionally necessary to clarify the anatomy, but this technique is used less frequently because of the risk of inducing life-threatening arrhythmias.
Anomalous aortic origins of the coronary arteries are usually minor defects, but a potentially dangerous abnormality exists when the left main coronary artery arises from the right coronary sinus and passes between the pulmonary artery and aorta. This defect has been associated with cardiac symptoms and sudden death, as has the origin of the right coronary artery from the left coronary sinus (usually when the right coronary is dominant). The etiology of ischemia in both defects is thought to be related to the acute angle of origin and slit-like orifice of the anomalous vessel and the extrinsic compression created by the apposing walls of the aorta and pulmonary artery. These defects usually present in older patients. Symptomatic patients are treated surgically by coronary artery bypass.
Myocardial bridging occurs when a segment of an epicardial coronary artery (usually the left anterior descending) takes an intramyocardial course over a short segment. Although this is a common incidental finding at cardiac catheterization, this defect has been associated in some cases with myocardial ischemia. Treatment involves dividing the muscle bridge to free the coronary, coronary bypass beyond the bridge, or transcatheter stenting.
Coronary aneurysms occur rarely, usually in conjunction with an inflammatory condition such as Kawasaki syndrome, polyarteritis nodosa, Takayasu arteritis, or syphilis. Coronary aneurysms may thrombose or lead to distal coronary stenosis or embolization. Rupture occurs uncommonly. Treatment ranges from antiplatelet therapy to coronary artery bypass grafting, and possible transplantation.
All symptomatic fistulas should be occluded, either surgically or by transcatheter techniques. In some cases, coronary bypass grafting may be necessary when distal flow is compromised by fistula occlusion. Treatment of asymptomatic fistulas is controversial, but occlusion should probably be undertaken when significant left-to-right shunting is present.
Surgical repair is indicated for all patients with ALCAPA. Historically, the initial surgical approach involved ligation of the proximal left coronary artery. This served to eliminate coronary steal and allow perfusion of the left coronary system by collaterals from the right. Despite the ease of simple ligation, most centers have abandoned this approach in favor of establishment of a 2-coronary system, which offers better long-term freedom from ischemia. In older patients, this may be achieved by proximal ligation of the left coronary artery in conjunction with coronary artery bypass, ideally with a left internal mammary graft. Coronary bypass is technically difficult in neonates, and a number of alternative operations have been devised to create a direct connection between the aorta and the anomalous coronary artery. Most commonly, this can be achieved by removing the origin of the left coronary artery (along with a button of adjacent pulmonary artery) and reimplanting the vessel directly into the side of the aorta. Another approach involves creation of a side-to-side connection between the aorta and pulmonary artery with placement of an intrapulmonary baffle to direct flow from this connection to the anomalous left coronary ostium.
Survival following surgical repair of ALCAPA has improved over the years. Recent reports have suggested an operative mortality of 0%-6%. Ventricular function tends to normalize after surgery. In most patients, mitral valve function also improves, but for patients with severe mitral regurgitation, concurrent mitral valve repair may be indicated.
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