Chapter 51. Ascending Aortic Aneurysms

The Greek physician Galen first described superficial false aneurysms arising from venisection in the antecubital fossa and in gladiators injured during battle in the second century AD.1 Antyllos, during the same time period, distinguished between true and false aneurysms and attempted surgical treatment with proximal and distal ligation, opening of the aneurysmal sac, and removal of its contents.2

In 1542, the French physician Jean Francois Fernel described aneurysms, “in the chest, or about the spleen and mesentery where a violent throbbing is frequently observable.”3 In 1543, Andeas Versalius described a thoracic aortic aneurysm. In the late 1500s, Ambroise Paré described a death by a ruptured thoracic aortic aneurysm, and either Fernel or Paré proposed that syphilis played a causative role in some aortic aneurysms.1 In 1760, Morgagni reported the first cases of aortic dissection, and in 1773, Alexander Monro described three coats of the arterial wall and the destruction of the wall in the formation of true and false aneurysms.1

Peripheral arterial ligation was developed in the 1800s by John Hunter, who demonstrated safe and reproducible means of ligating certain peripheral arteries.4 Innovative measures used to cause thrombosis of aneurysms included the insertion of long segments of wire5 with the application of an electric current,6 and wrapping of aneurysms with cellophane or other irritating materials.7,8

In 1888, Rudolph Matas introduced obliterative endoaneurysmorrhaphy, in which stitches placed from within the aneurysm sac obliterated the arterial openings.9 This allowed closure of large aneurysms that would have been difficult to ligate externally. Recognizing the importance of maintaining arterial continuity for certain aneurysms, he subsequently devised techniques of restorative or reconstructive endoaneurysmorrhaphy, in which diseased segments of the aneurysm wall were resected and the remaining vessel wall was reconstructed to reestablish flow.10 The number of aneurysms to which these techniques could be applied, however, was very limited. The broad application of surgical treatment for major arterial aneurysms would have to await the development of satisfactory conduits and the techniques to insert them.

The first report of a descending aortic repair was described by Cooley and DeBakey in 1952. The technique involved lateral resection and aortorrhaphy performed on a saccular aneurysm without cardiopulmonary bypass.11 In 1956, Cooley and DeBakey performed replacement of the ascending aorta with a segment of homograft with cardiopulmonary bypass.12 Polyester cloth grafts were introduced by DeBakey, who discovered it in a Houston department store, and it soon became the artificial conduit of choice for aortic replacement.13 Technical improvements in graft replacements included the impregnation of polyester grafts with albumin, collagen, or gelatin, which has greatly reduced the blood loss through the grafts.14

Wheat and colleagues, in 1964, resected the ascending aorta and entire aortic root except for the aortic tissue surrounding the coronary arteries.15 They then performed a mechanical valve insertion and fashioned the proximal tube graft to accommodate the coronary arteries, which were left in situ. The first composite aortic root replacement was performed by Bentall and De Bono in 1963 to treat an ascending aortic aneurysm in a patient with Marfan's syndrome who had severe thinning of the aortic wall in the sinus segment.16 The original technique involved hand sewing a Starr no. 13 mechanical prosthesis to a preclotted graft (Fig. 51-1). An inclusion-type technique with aortic wrap in which the coronary buttons were left in situ and anastomosed to holes made in the graft was performed. Because of concerns about coronary malposition, in 1981 Cabrol and colleagues described the use of an 8- to 10-mm Dacron graft to attach to independently mobilized coronary artery buttons.17 Techniques eventually evolved to the current method of individual coronary button reimplantation as described by Kouchoukas and Karp with end-to-end anastomoses as opposed to the inclusion technique, which tended to be prone to pseudoaneurysm formation.18

The aortic root is an extension of the left ventricular outflow tract and that provides the scaffolding for the elements of the aortic valve and connects to the descending aorta. Its components include the aortic valve cusps, the sinuses of Valsalva, the aortic annulus and subcommissural triangles, and the sinotubular junction (Fig. 51-2).19 The aortic valve cusps attach to the aortic annulus at hinge point following a semilunar contour being a three pointed crown-type arrangement not a circular or oval ring. The annular tissue itself is typically 50 to 60% fibrous tissue along the hinge point between the aortic and mitral valves as well as the membranous portion of the septum, and the remainder is muscular. Small projections of collagen anchor the aortic root to the ventricular muscle.20 The apices of the attachments of the cusps to the aortic annulus are known as commissures, and the most superior aspect of the commissures interrelates with the sinotubular junction. The sinotubular junction is a ridge that marks the beginning of the ascending aorta. The sinotubular junction diameter is typically 15 to 20% smaller than annular diameter in younger patients.21 With aging the sinotubular junction diameter becomes larger. When the sinotubular junction is more than 10% larger than the annular diameter, there is frequently resultant aortic insufficiency because the leaflets were no longer coapt owing to displacement of the commissures.

Between the sinotubular junction and the aortic annulus are expanded segments of the aorta referred to as the sinuses of Valsalva. The sinuses form a cloverleaf rather than circular alignment when viewed in cross-section (Fig. 51-3).22 Dilatation of the aortic sinuses and annulus are referred to as aortoannular ectasia. Each sinus is named for its corresponding coronary artery right, left, and noncoronary.

The noncoronary sinus is anatomically related to the left and right atria as well as the transverse sinus. The left coronary sinus anatomically relates to the left atrium, and the right coronary sinus is related to the right atrium and right ventricle. The subcommissural triangle between the right and noncoronary arteries is anatomically related to the conduction system within the membranous septum as well as the septal leaflet of the tricuspid valve. The left and noncoronary subcommissural triangle are related to the anterior leaflet of the mitral valve. The ascending aorta starts at the level the sinotubular junction and ascends to the level of the takeoff of the innominate artery.

The ascending aorta histologically contains a high proportion of compliant elastic tissue allowing it to serve as a reservoir and that stores kinetic energy from the systolic pulse wave as it expands and uses it to maintain flow during diastole via elastic recoil. The ascending aorta is a three-layered structure composed of a smooth intimal layer composed of a single layer of endothelial cells adhered to a basal lamina; a medial layer composed of layers of elastin sheets, collagen, smooth muscle cells, and extracellular matrix; and an outer layer of adventitial tissue, which includes the vaso-vasorum and nerves.23 The elastin content of the aorta decreases distally and in the abdominal aorta is less than half of that in the ascending aorta.24 The principal biologic causes of aneurysm formation in the ascending aorta are related to degenerative processes in the elastic media, as compared with primarily atherosclerotic changes in the descending and abdominal aortas.25

Ascending aortic aneurysm formation is the result of several biologic and mechanical mechanisms. Disruption of the balance between homeostatic mechanisms within the aortic wall, including elastic and collagen elements, proteoglycans, proteolytic enzymes and their inhibitors, and inflammatory mediators, causes a spectrum of aortic pathology that manifests in the final pathway as aortic enlargement, eventually leading to rupture or dissection. Fragmentation of the extracellular matrix of the aortic media occurs because of matrix-degrading enzymes such as matrix metalloproteinases and cathepsin groups.26–30 Matrix metalloproteinases comprise a family of proteases that are capable of degrading virtually all components of the extracellular milieu and perform a variety of tasks necessary for normal homeostasis, including maintenance of the dynamic integrity of the extracellular structure within arteries.26–28 Aneurysms form as elastic layers fragment, smooth muscle cells become dysfunctional and eventually elastic, and smooth muscle components are replaced with a cystic appearing mucoid material (Fig. 51-4).31 This process is referred to as cystic medial degeneration. The term cystic medial necrosis has also been applied to this condition, but has been largely abandoned because there is no true necrotic process involved. To a lesser extent, mild degeneration of the aortic wall is common with advanced age and is responsible for the slow dilation of the ascending aorta with age. Smoking tends to exacerbate this degeneration.32

Mechanical changes to aortic wall characteristics such as alterations in cross-sectional symmetry, compliance, and stress–strain relationships likely predate dilatation. The Young–Laplace relationship describes the association between aortic diameter and wall tension, in which increases in aortic wall diameter lead to increases in wall stress at similar pressures (tension = pressure × radius). Changes in aortic wall compliance, broadly defined as the change in volume of the vessel with a change in pressure, lead to increased stress applied to the aortic wall during the systolic impulse and further exacerbate the biologic derangements leading to aneurysm formation.33 The coupling between mechanical forces on the arterial wall and the biochemical changes leading to aneurysm formation (mechano-transduction) are not yet clearly elucidated.

Degenerative aortic aneurysms cause asymmetric enlargement of the ascending aorta because the segment of aorta along the inner curvature is adherent to the pulmonary artery34; hence, there is significant rightward and anterior displacement of the aortic wall. This causes a relative elongation of the ascending aorta in an asymmetric fashion, which tends to push the heart into a horizontal arrangement. This also causes a significant change in the orientation of the aortic valve annulus to a more oblique arrangement.34 Aneurysmal widening will typically involve the aorta to the level of the sinotubular junction and frequently involves the noncoronary sinus to a lesser extent.35 This widening at the level of the sinotubular junction is responsible for aortic insufficiency in these cases, and frequent placement of tube graft to the sinotubular junction will resolve significant central aortic insufficiency. The left and noncoronary sinuses are fairly normal in these cases. The noncoronary aortic valve cusp may be elongated along its free margin to compensate for the asymmetric enlargement of the noncoronary sinus.

Marfan's Syndrome

Marfan's syndrome is an autosomal dominant syndrome with complete penetrance. Up to 25% of Marfan cases are from sporadic dictation in the overall incidence is one per 3000 to 10,000 live births.36 Traditionally, it is thought to have been caused by alterations in the gene (FBM1) coding the aortic wall protein fibrillin-1, leading to elastin derangement, medial degeneration, and aneurysm formation.37,38 More recently, homology between fibrillin-1 molecules and latent TGF beta-binding proteins has led investigators to infer that altered sequestration of the latent form of TGF beta in the extracellular matrix may increase TGF beta activity, which negatively affect smooth muscle development and the extracellular matrix.39 Approximately 80% of patients with Marfan's syndrome develop aortic root aneurysms and nearly half develop mitral regurgitation.40 The clinical manifestations of Marfan's syndrome involve multiple organ systems because it is a systemic disease. Diagnosis has traditionally been made using the Ghent criteria, although it is now made definitively using genotyping.41 Anatomically, Marfan's syndrome results in severe aortoannular ectasia and massively dilated sinuses and aortic annulus (Fig. 51-5).

More recently, reports have shown that the use of angiotensin-converting enzyme inhibitors can prolong the life expectancy of smooth muscle cells in the aortic tissue of Marfan patients via an angiotensin-2 type II receptor blockade mechanism, which may antagonize TGF beta.42 This has led to the clinical application of the angiotensin receptor blocker losartan as a prophylactic therapy to diminish aortic degeneration and aneurysm formation, which has been shown in animal models to be effective when given in the early stages of the disease.43 A small clinical study of 18 pediatric patients also showed decreased aortic growth rate with treatment of losartan.44

Loeys-Deitz Syndrome

Loeys-Deitz syndrome is a more recently described autosomal-dominant syndrome.45 Rather than a fibrillin-1 defect, however, there is a mutation in transforming growth factor (TGF) beta receptor 1 and 2. Characteristics of Loeys-Deitz syndrome include cleft palate, bifid uvula, scoliosis, orbital hypertelorism, pectus deformities, developmental abnormalities, and congenital heart defects, including persistent patent ductus arteriosus and atrial septal defects.45 Patients may phenotypically have characteristics that overlapped between Loeys-Deitz syndrome and Marfan's syndrome.46 Histologically, it is associated with increased medial collagen and a subtle but diffuse form of elastic fiber fragmentation and extracellular matrix deposition.47 Loeys-Deitz syndrome has a more rapid clinical course than Marfan's syndrome and prophylactic aortic root replacement or reimplantation is often recommended at younger ages and with smaller aortic dimensions.

Ehlers-Danlos Syndrome

Ehlers-Danlos syndrome is caused by either sporadic mutation or inherited autosomal dominant trait, resulting in a connective tissue disorder derived from defective type III collagen synthesis. The type IV variant of the Ehlers-Danlos syndrome is associated with spontaneous arterial rupture. Most commonly this occurs in the mesenteric or carotid arteries. However, spontaneous rupture of the descending aorta and aortic arch has been described.48 The arterial wall of these patients is extremely thin and friable. Ascending aortic involvement may occur as a consequence of retrograde extension of a primary brachiocephalic branch pathology.

Infections and systemic inflammatory disorders can occasionally cause damage to the wall of the ascending aorta, leading to aneurysm formation. Frequently, despite high-quality preoperative imaging and even with intraoperative tissue pathology, is not possible to definitively distinguish between the different possible etiologies.

Ascending aortic aneurysms caused by infection are extremely uncommon. Such mycotic ascending aortic aneurysms are frequently related to concomitant left-sided valvular endocarditis. Most common organisms include, in order of decreasing frequency, Staphylococcus aureus, Staphylococcus epidermidis, Salmonella, and Streptococcus.49 In cases of atherosclerotic aneurysm, if there is intraluminal clot in the ascending aorta, transient bacteremia may lead to infected clot leading to a mycotic aneurysm.⁵⁰

Syphilis, caused by the spirochete Treponema pallidum, was the predominant cause of ascending aortic aneurysms in the preantibiotic era and accounted for 5 to 10% of all cardiovascular deaths.51 Typically syphilitic aortitis involves the thoracic aorta with a particular predilection for the ascending aorta, likely owing to its rich vascular and lymphatic supply. The pathologic process involves a multifocal lymphoplasmacytic infiltrate of the vasa vasorum leading to degeneration of the medial elastic fibers. The intima develops wrinkles ridges and plaques described as a “tree bark appearance” (Fig. 51-6).52 Inflammation around the coronary artery ostia may lead to high-grade proximal occlusions. The inflammatory process may either be patchy or diffusely involve a large section of aorta. Once established, treatment of syphilis with antibiotics does not reverse the vascular lesions.

Other systemic arteritis conditions may also produce ascending aortic aneurysms. Takayasu's arteritis is associated with inflammation of the vasa vasorum and medial necrosis, and may also have intimal changes similar to syphilis. It is typically seen in women between 15 and 30 years of age and frequently involves occlusive lesions to major branch vessels of the arch.53 Although syphilis aortitis often in leads to rapid aneurysmal degeneration, this is much less common in Takayasu's aortitis, occurring only 15% of cases.54 Giant cell arteritis is a systemic arteritis that occurs in elderly patients, most commonly affecting the temporal artery. It is also more common in females and is also associated with polymyalgia rheumatica. Giant cell arteritis is an inflammatory process with inflammatory infiltration with lymphocytes, plasma cells, and histiocytes. There is a variable presence of giant cells.55 Aortitis leading to aortic aneurysm may also be associated rarely with Behçet's disease, rheumatoid arthritis, sarcoidosis, ankylosing spondylitis, lupus erythematosus, and Wegener's granulomatosis.

Bicuspid Aortopathy

Bicuspid aortic valve is a complex familial syndrome, with a male predominance of 3 to 1.56 It is also associated with Turner's syndrome. There is a 9% prevalence of bicuspid aortic valve disease in first-degree relatives of patients with bicuspid aortic valve disease.57 More than half of patients with aortic coarctation have an associated bicuspid aortic valve.58 Several genetic defects have been implicated in the formation of bicuspid aortic valve disease; however, no single genetic etiology has been derived. Aortic dilatation is frequently associated with bicuspid aortic valve disease; however, the mechanism for this is not well delineated. Originally thought to be a sequela of poststenotic dilatation, aortic aneurysm formation in patients with bicuspid aortic valve may occur without any significant aortic stenosis, although there is clearly flow perturbation in the proximal sinuses of Valsalva and descending aorta in patients with bicuspid aortic valve.59 Recent investigation has shown that embryologically, the aortic valve and ascending aorta arise from the neural crest cells, implicating a potential common mechanism for the development of a bicuspid aortic valve and subsequent aneurysm formation.60 The aortic wall in bicuspid aortic valve disease patients shows increased elastic fragmentation, fibrillin-1 deficiency, matrix disruption, increased levels of matrix metallic proteinases, and smooth muscle cell apoptosis.60–65

Fazel and colleagues using a cluster-type analysis identified four distinct patterns of aortic dilatation including: aortic root alone (13%), ascending aorta alone (10%), ascending aorta and proximal transverse arch (28%), and aortic root, ascending aorta, and proximal transverse arch (45%) (Fig. 51-7).66 This study suggests that for younger patients, definitive treatment of bicuspid aortic valve disease with aortic dilatation requires strategies that address the aortic root, ascending aorta, and proximal transverse hemiarch. It is advisable to perform an aggressive hemiarch, resecting all aortic tissue along the lesser curve to the level of the subclavian artery takeoff in younger bicuspid aortic valve patients to eliminate as much of the diseased aorta as possible. However, total arch replacement with brachiocephalic branch reimplantation is rarely necessary because the aneurysmal component rarely involves the distal aspect of the transverse arch.

Isolated Sinus of Valsalva Aneurysm

Aneurysms of the sinuses of Valsalva that occur as isolated lesions are rare abnormalities caused by either a congenital defect in the continuity between the medial layer of the affected sinus and the aortic valve annulus or, less commonly, acquired causes such as endocarditis, syphilis, tuberculosis, focal dissection, or iatrogenic causes.67 They are more common in males and may be associated with subaortic stenosis, ventricular septal defects, and aortic insufficiency. In greater than 90% of cases, they involve the right coronary sinus (Fig. 51-8).68,69 The noncoronary sinus of the second most common location and these aneurysms are extremely uncommon in a left coronary sinus. They are generally asymptomatic until they rupture, when they usually cause intracardiac shunts. Right sinus of Valsalva aneurysms typically ruptures into the right ventricle, effectively causing a hemodynamic defect similar to a ventricular septal defect. Aneurysms of the noncoronary sinus typically rupture into the right atrium and the left coronary sinus ruptures into the pulmonary artery or left ventricle. Occasionally an unruptured left coronary sinus of Valsalva aneurysm may compress the left main coronary artery.69

Other Familial Aneurysms

Specific families often exhibit strong tendencies for thoracic aortic aneurysm formation without any clearly definable connective tissue disorder such as Marfan's syndrome. There is no defect in fibrillin-1 expression in these patients. It is postulated that aneurysms in these patients are inherited in an autosomal-dominant manner with no gender bias, incomplete penetrance, variable expression, and variable age of aneurysm onset.70 A wide variety of potential genes have been implicated and relate to processes involving collagen formation, extracellular matrix hemostasis, and smooth muscle proteins.71–74

Symptoms

Most ascending aortic aneurysms are asymptomatic when diagnosed, being incidentally noted on chest x-ray or echocardiogram. Anterior chest pain is the most frequent symptom. The pain may be acute in onset signifying impending rupture, or a chronic gnawing pain from compression of the overlying sternum. Occasionally signs of superior vena cava or airway compression are present. Hoarseness resulting from stretch injury of the left recurrent laryngeal nerve suggests involvement of the distal aortic arch or proximal descending thoracic aorta. Less commonly, aneurysms of the ascending aorta or aortic root can rupture into the right atrium or the superior vena cava, presenting with high-output cardiac failure, or bleed into the lungs with ensuing hemoptysis. Acute dissection of the ascending aorta presents with severe tearing pain in greater than 75% of patients.75

Physical Examination

Physical examination is often unremarkable. If there is related aortic insufficiency, a widened pulse pressure or diastolic murmur may be present. If dilation is isolated to the ascending aorta, however, the aneurysm can reach large dimensions without producing physical findings. A thorough vascular examination should be carried out to look for any concomitant peripheral vascular disease, carotid disease, or abdominal aortic aneurysm. Abdominal aortic aneurysms may be present in 10 to 20% of patients with atherosclerotic involvement of an ascending aortic aneurysm.76

Electrocardiogram

With significant aortic insufficiency, left ventricular hypertrophy or strain is evident. Patients with generalized atherosclerosis may show evidence of concomitant coronary artery disease or previous myocardial injury.

Chest Radiography

Many asymptomatic ascending aortic aneurysms are first detected on chest x-ray. The enlarged ascending aorta produces a convex contour of the right superior mediastinum (Fig. 51-9A). In the lateral view, there is loss of the retrosternal air space (Fig. 51-9B). Aneurysms confined to the aortic root can be obscured by the cardiac silhouette and may not be evident on chest radiograph.77

Echocardiography

Transesophageal echocardiography (TEE) is a portable diagnostic tool that accurately detects and differentiates among ascending aortic aneurysms, dissections, and intramural hematoma (Fig. 51-10).78–80 TEE is an invasive imaging modality and carries a small risk of esophageal perforation, respiratory compromise, and hemodynamic instability. Imaging of the distal ascending aorta is obscured on TEE by air in the tracheobronchial tree, with up to 40% of its distal extent not well visualized, although this is somewhat mitigated with the use of modern multiplanar probes.81 Although somewhat operator dependent, TEE provides a reliable technique to measure the annular, sinus, sinotubular junction, and ascending dimensions. It is uniquely well suited to examine the most proximal aspects of the aortic root, which are often blurred by motion artifact on computed tomography scans. Transthoracic echocardiography is far less reliable but may be useful for assessing the severity of aortic regurgitation.

Computed Tomography

Contrast-enhanced computed tomography (CT) is the most widely used noninvasive technique for imaging the thoracic aorta. CT scanning provides rapid and precise evaluation of the ascending aorta in regard to size, extent, and location of the disease process (Fig. 51-11). CT scanning detects areas of calcification, and modern scanner accurately identify dissections and mural thrombus.82 CT scan technology has evolved with multidetector scanners such that the entire thoracic aorta can be evaluated on one breath-hold and the distance between axial slices can be as small as 0.5 mm. Three-dimensional volume rendering is a highly useful tool for determining true in-plane aortic diameters and the proximal and distal extent of aortic disease relative to the arch vessels, which can aid the surgeon in operative planning (Fig. 51-12). Ideally, the entire thoracic and abdominal aorta should be examined for evidence of concomitant aneurysm disease in the arterial tree. Gating to the electrocardiogram during image acquisition eliminates the motion artifact that may be seen in the most proximal aspects of the aortic root and can also allow for assessment of the coronary arteries.83 The main disadvantage of CT scans is the need for contrast solution for optimal resolution, which may be contraindicated in those patients with renal insufficiency or a history of a dye allergy. Noncontrast CT scans allow for assessment of aortic diameters but cannot identify dissection flaps or other acute pathologies.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) can provide axial and three-dimensional reconstruction of the ascending aorta with the avoidance of iodinated contrast agents and radiation exposure. Contrast-enhanced MR angiography with gadolinium allows more precise measurements of the aorta and its major branches with images comparable with conventional angiography.84 MRI scanners are relatively unsuitable for those patients connected to mechanical ventilators or hemodynamic monitoring equipment. MRI is more expensive, less readily available, and requires significantly more acquisition time than CT scanning and is used less frequently.

Elective aortic replacement is used as a means to prophylactically prevent aortic catastrophe such as dissection and rupture, which carry high mortality. Recent data from the International Registry of Acute Aortic Dissections (IRAD) shows an operative mortality for emergent type A aortic dissection repair of 26%, although this is generally lower in more experienced centers.85 Bickerstaff and colleagues examined the natural history of 72 patients who were diagnosed with aortic aneurysms and did not undergo surgery.86 Over a 5-year follow-up period, 74% of patients experienced aortic rupture or dissection (Fig. 51-14). Of these, 94% died. The overall 5-year survival was only 13% in untreated aneurysm patients, compared with 75% in control patients without aortic aneurysms.

Traditionally, the most important criterion for ascending aortic replacement on an elective basis is maximal aortic diameter. In natural history studies by Coady and colleagues, patients with 3.5- to 3.9-cm aortic aneurysms were very unlikely to rupture within 3 to 4 years, and each incremental 1-cm increase from this point increased rupture risk (Fig. 51-15).87 Patients with aneurysms greater than 5 cm showed substantially higher dissection and rupture risk within the first year. Using a logistic regression model, they found that the aneurysm with maximal diameter of 6.0 to 6.9 cm had a 4.3 times greater increased risk of rupture or dissection than an aneurysm that is 4.0 to 4.9 cm in diameter. Growth rates for aortic aneurysms less than 4 cm are about 0.1 cm per year, and this increases gradually as aortic size increases up to 0.4 cm per year.88,89 Uncontrolled hypertension, smoking, and presence of connective tissue disorders are associated with more rapid aortic growth.88 Patients with Marfan's syndrome are at particularly high risk for rupture or dissection of smaller sizes, and dissection is frequently seen with a maximal ascending aortic dimension of less than 5 to 6 cm (Fig. 51-16).90 Strikingly, the average age of death for untreated patients with Marfan's syndrome is 32 years, with complications of the aortic root being responsible for 60 to 80% of these deaths.91 Marfan's patients with a family history of early dissection or rupture are at the highest risk for aortic catastrophe occurring at smaller dimensions.92

Although size clearly correlates with rupture risk, it is important to note that many aortic dissections occur in ascending aortas that are less than 5.5 cm in diameter. In the IRAD registry, more than 59% of 591 enrolled patients with acute type A aortic dissections had maximum aortic dimensions less than 5.5 cm and 40% were less than 5.0 cm (Fig. 51-17).93 As the understanding of the biologic mechanisms behind aortic aneurysm formation improve in the future, serum biologic markers and sensitive imaging techniques that can detect subtle changes in aortic strain characteristics or compliance may provide more accurate identification of the high-risk aorta.

Therapies designed to limit the growth of aortic aneurysms are targeted at mechanisms to diminish stress on the aortic wall and prevent deleterious degenerative biochemical changes. In general, patients with aortic aneurysms should avoid high-intensity isometric exercise, such as weightlifting, because aortic pressures may increase rapidly and exert significant stress on the aortic wall. Weight lifting restriction should be less than one-third to one-half of the patient's body weight. Additionally, exercises with rapid bursts of acceleration and deceleration, such as basketball, may place excessive stress on the aortic wall.

Anti-impulse therapies are the mainstay treatment for thoracic aortic aneurysms. Because of their negative chronotropic and inotropic effects, beta-blockers are typically used as a first-line treatment.94 The primary goals of beta-blocker therapy are to decrease overall blood pressure and decrease the change in aortic pressure over time (dP/dT), to diminish the stress applied to the aorta in systole and thereby limit damage to the media layer. The rationale for using beta-blockers was initially established with an ex vivo plastic model of aortic dissection by Wheat and colleagues in which a tear created in an artificial intimal layer of rubber cement in the plastic tubing propagated less when the pulse pressure was artificially flattened, whereas variation of mean blood pressure and flow rates had no effect.95 Studies performed on turkeys, which are uniquely prone to aortic dissection, showed the combination of sodium nitroprusside and propranolol were effective at preventing rupture, whereas lowering blood pressure with nitroprusside alone was ineffective and may have actually increased dP/dT owing to reflex sympathetic stimulation, causing increased chronotropy and inotropy.96 In a landmark study by Shores and colleagues, young patients with Marfan's syndrome randomized to a regimen of beta-blocker therapy had significantly less aortic dilatation over a 10-year follow-up period (Fig. 51-18), and also had a lower incidence of a composite end point of death, congestive heart failure, aortic dissection, severe regurgitation, or aortic root surgery versus controls.97 These results have been extrapolated to a wider variety of patients with ascending aortic aneurysms in whom beta-blockade is used extensively.

Nonelective Indications

Any new onset acute dissection, rupture or intramural hematoma generally warrants immediate surgery. The presence of symptoms of chest pain in patients with ascending aortic aneurysms greater than 4.5 to 5 cm is a sign of impending rupture and should also be managed operatively with expediency. Acute severe congestive heart failure secondary to root dilatation and loss of sinotubular junction definition either from rapid aneurysm expansion or chronic dissection also warrants early operative management, although aggressive diuresis and cardiac optimization for one to two days before surgery is frequently helpful.

Elective Indications

Despite the limitations of size criteria, decisions to intervene are still largely decided based on maximal aortic diameter and growth rate. For degenerative aneurysms in the absence of connective tissue disorders or other cardiac pathology, elective repair is reasonable at an absolute maximal diameter of 5.5 cm.98 A growth rate of greater than 1 cm per year is generally accepted as a strong indication to proceed with surgery for degenerative aneurysms regardless of diameter.99 Some groups have also advocated the use of normalized aortic dimensions to body size to provide a more accurate reflection of the aneurysm dimension for an individual patient.100

The aortic ratio is calculated as measured diameter divided by predicted diameter for a given age body surface area. Using this method, elective replacement is warranted at an aortic ratio of 1.5 in an asymptomatic patient without a connective tissue disorder or other complicating factor.101 This leads to intervention at a size of only 4.8 to 5.0 cm in an adult less than 40 years of age with a body surface area of 2 m2.101 Because the ascending aorta normally increases in size with age, the diameter for intervention is higher in a patient more than 40 years old.

Special Considerations

Patients with Marfan's syndrome are at higher risk for rupture, and the ascending aorta should be replaced prophylactically at a diameter of 4.5 cm or an aortic ratio of 1.3 to 1.4.101,102 Among patients with bicuspid aortic valves, current consensus is that aortas greater than 4.5 cm or aortic ratio of 1.3 to 1.4 should be replaced at the time of aortic valve replacement.101,103 In the context of a well-functioning bicuspid aortic valve, the ascending aorta should be replaced at a maximal dimension of 5.0 cm.104 In chronic aortic dissections, in which the external aortic wall is supported only by the residual outer third of the medial and adventitial layers, replacement should be performed when aortic diameters reach 4.5 cm or ratio of 1.3 to 1.4 because of the intrinsic weakness of the aortic wall.101 In the setting of connective tissue disorders, bicuspid aortic valve, or chronic dissection, a growth rate of greater than 0.5 cm per year should warrant repair. Pseudoaneurysms, which are frequently from previous aortic suture lines, should be repaired on diagnosis because of high rupture risk related to their extremely thin walls.

In younger patients, in whom aortic root reimplantation is preferred to avoid lifelong anticoagulation, earlier repair may prevent the development of aortic valve cusp pathology and improve the chances of successful repair. Among patients undergoing aortic valve replacement who have ascending aortic aneurysms, Prenger and colleagues reported a 27% incidence of aortic dissection if the aorta was greater than 5 cm versus 0.6% incidence if aortic size was normal.105 In general, in the setting of other cardiac surgery, ascending aortas with a maximal dimension of 5.0 cm or a ratio of 1.5 should be replaced.101,105

Nearly one-third of patients undergoing surgery for thoracic aortic disease have chronic obstructive pulmonary disease.106 Patients with suspect pulmonary function should have spirometry and room air arterial blood gases. Smoking cessation, antibiotic treatment of chronic bronchitis, and chest physiotherapy may prove beneficial in elective situations. Normal renal function should be ensured with the appropriate blood work, and abnormal results should prompt further investigation. Because unaddressed severe carotid disease is a risk factor for stroke during ascending aortic operations, patients greater than age 65 should have duplex imaging of their carotids.107 Younger patients with peripheral vascular disease, extensive coronary artery disease, carotid bruits, or a history suspicious for cerebral ischemia should be investigated as well. CT or MRI of the thoracic and abdominal aorta is usually indicated. Coronary angiography should be performed in all patients to evaluate for significant coronary atherosclerosis, and lesions with greater than 50 to 60% stenosis should be bypassed. Coronary angiography also helps define the coronary anatomy to identify anomalous or intramural coronary arteries, which may complicate root replacement.108

Choice of procedure when managing ascending aortic aneurysms is predicated on a detailed understanding of individual patient anatomy and pathophysiology. The potential operative decisions include whether to replace the aortic valve, aortic sinuses, ascending aorta, or aortic arch. Any combination of these procedures is theoretically possible. A systematic approach to evaluate the aorta and aortic root begins with determining if there is a suspicion for connective tissue disorder. Patients with Marfan's syndrome, Ehler's Danlos, Loeys-Dietz, bicuspid valve–related aortopathy, or strong family history of aortic dissection or rupture should generally be treated more aggressively by replacing the sinus segment, ascending aorta, and proximal arch, because late reintervention is more likely in this group.109 Proximal reconstruction in these patients may be accomplished by either root replacement or a valve-sparing root reimplantation procedure.110

The next step is to determine the pathology of the aortic valve. Moderate or worse aortic stenosis with or without insufficiency generally requires replacement, whereas the management of pure aortic insufficiency is more complex. Aortic insufficiency caused solely by dilatation of the sinotubular junction, typically from an atherosclerotic aneurysm in an elderly patient, may be fully addressed with tube graft replacement of the ascending aorta alone with anastomosis to the sinotubular junction (Fig. 51-19). Care must be taken in this instance to appropriately size the graft to within 10% of the annular dimension to allow full coaptation of the aortic valve leaflets.111 The sinus segment must also be closely interrogated. If it is particularly thin or aneurysmal, it should be replaced. Normal dimensions of the sinus of Valsalva are typically 30 to 32 mm when the aortic annulus measures 23 to 24 mm and the sinotubular junction measures 24 to 25 mm.112 If there are aneurysmal sinuses and annular dilatation (aortoannular ectasia), but the leaflets appear fairly normal, then a valve-sparing aortic valve reimplantation is often feasible (Fig. 51-20). Technical details of this procedure are discussed in a previous chapter. If the annulus or sinuses are dilated and the leaflets are abnormal and not repairable, root replacement is performed. Prosthesis options include prefashioned composite mechanical root prostheses, sewing a stented tissue valve to a conduit, or using a porcine bioroot. Prosthesis selection is based on several competing factors, including the elevated hazard for structural deterioration of biologic prostheses in younger patients, anticoagulant-related complications with mechanical prostheses, complexity and difficulty of performing future redo root replacements for bioprosthetic failure, and the growing trend toward the avoidance of warfarin in younger patients. The innovation of transcatheter valves, which have the potential to extend the life of a biologic root prosthesis without repeat sternotomy, has generated interest in using these prostheses in younger patients.113 Pulmonary autografts may also be used as root replacements, but their practicality in aneurysm patients is somewhat limited because degenerative aneurysms tend to occur in older patients who would not benefit from the durability of the pulmonary autograft. Younger aneurysm patients, who could potentially benefit, frequently have bicuspid pathology or connective tissue disorders that may lead to early valve failure. Bicuspid patients have been shown to have significant histologic arterial wall derangements, including the cystic medial necrosis, elastic fragmentation, and changes in the smooth muscle cell orientation in the autograft root.114

In patients in whom there is an isolated dilatation of the noncoronary sinus in degenerative aneurysms with preserved sinus dimensions in the coronary sinuses, In the noncoronary sinus may be individually excised and a “tongue” of the ascending aortic graft may be used to reconstruct this sinus with the rest of the graft anastomosed above the native annulus; that is, a Yacoub-type remodeling procedure isolated to the noncoronary sinus.115 Such a procedure carries the risk of late dilatation or suture-line disruption because the remaining aortic tissue is often thin and weak. It is also possible to perform an isolated noncoronary sinus reimplantation as described by David and Feindel.116 Unless operative risk is prohibitive, it is preferential to perform a full root replacement or reimplantation in such patients rather than treat only one sinus.

In patients in whom the aortic valve needs to be replaced because of leaflet pathology, the sinus segment is not aneurysmal, and there is an ascending aneurysm, a modified Wheat procedure with replacement of the aortic valve and placement of a tube graft to the sinotubular junction is used (Fig. 51-21).15 This approach is especially useful in elderly patients who have mild to moderate sinus segment dilatation, but a root replacement carries significant extra perioperative risk and the likelihood of future proximal reoperation is negligible.

Distal repair may be done as either a total arch, hemiarch, open distal, or clamped distal anastomosis. Total arch replacement with or without elephant trunk extension is typically reserved for patients with full arch aneurysms extending into the thoracic aorta or mega-aorta syndrome. Aneurysmal extension into the proximal aortic arch is a common variant and is well treated with an aggressive hemiarch. Resection of the ascending aorta to the innominate artery on the greater curve and to the level of the subclavian takeoff on the lesser curve provides excellent protection from future aneurysmal degeneration of the arch (see Fig. 51-21). Although clamped techniques for the distal anastomosis are suitable for isolated root pathologies such as complex endocarditis repair, in aneurysm cases it is preferable to excise the cross-clamped portion of aorta and perform an open distal anastomosis.

Monitoring and Anesthesia

All procedures are performed using central venous access and a pulmonary artery catheter. Location of arterial line for blood pressure monitoring should be discussed with the anesthesia team preoperatively, although generally right radial is preferred. Nasopharyngeal and bladder temperature monitors are used. Bilateral near-infrared spectroscopy (NIRS) is employed to provide real-time estimation of cerebral saturation throughout the bypass run.117 Precipitous drops in cerebral saturations are managed with increasing perfusion pressure and hematocrit to the cerebral circulation. In circulatory arrest cases, EEG monitoring is also employed to ensure EEG silence during interruption of cerebral circulation.

Transesophageal echocardiography plays a critical role in diagnosis, particularly of degree of aortic insufficiency and sinus segment and sinotubular junction anatomy that is not well assessed by CT angiography. It is also critical for hemodynamic management separating from cardiopulmonary bypass.

Anesthesia management includes fentanyl, 25 to 50 μg/kg; midazolam, 0.1 to 0.2 mg/kg; isoflurane, 0.5 to 1.5%, end-tidal concentration, in oxygen and pancuronium, 0.1 to 0.2 mg/kg. Aminocaproic acid is dosed initially as an intravenous bolus of 5 g, followed by a maintenance intravenous infusion of 1 g/h and stopped within 2 hours of patient admission to the intensive care unit. Pharmacologic adjuncts in circulatory arrest cases include 1 g of methylprednisolone, 1 g of magnesium sulfate, 2.5 mg/kg of lidocaine, and 12.5 g of mannitol.118

Circulation Management

Cannulation strategies vary significantly with individual pathology and the modern cardiovascular surgeon must be proficient in several different techniques. With experience, ascending aortas as large as 7 cm may be directly cannulated. This can be done with the traditional stab technique or using a Seldinger technique over a wire in thin-walled aortas. In aneurysms that terminate before the innominate artery, the transverse arch is easily directly cannulated. In cases in which antegrade cerebral perfusion is required, either the ascending aorta may be cannulated directly if using selective direct perfusion cannulas or the right axillary artery may be employed. Right axillary artery cannulation, which has grown in popularity in recent years, should be performed through an 8- or 10-mm Dacron graft anastomosed end-to-side to the axillary artery, because there is risk of dissection from direct cannulation of this friable artery. In some instances, femoral artery cannulation can be employed, but should be avoided in patients with atheroma in the thoracic aorta by CT scan or TEE.

A standard two-stage venous cannula is used unless performing concomitant mitral or tricuspid surgery. For retrograde cerebral perfusion, a 24-French wire reinforced cannula is placed cephalad to the azygous vein in the superior vena cava and secured with a caval tape. Cooling is performed maintaining less than a 2 to 3°C gradient between arterial inflow temperature and venous return temperature to ensure even cooling. Rather than arbitrarily choosing a particular time or temperature threshold, cooling to EEG silence provides maximal potential brain protection. Data from Cheung and colleagues has shown that only 60% of subjects undergoing hypothermic circulatory arrest achieve EEG silence at a core temperature of 18°C or a cooling time of 30 minutes.119 In cases in which EEG monitor is not available, a safer technique is to cool for a minimum of 50 minutes, at which point 100% of patients have EEG silence.

Retrograde Cerebral Perfusion

Retrograde cerebral perfusion with oxygenated blood is adjusted to maintain a right internal jugular venous pressure of 25 mm Hg, a flow rate of 200 to 300 cc/min, with the patient in an approximately 10-degree Trendelenburg position.120 Minimal exsanguination into the pump is performed upon cessation of bypass to facilitate later deairing. RCP may be initiated via a Y-connection to the arterial line or from the cardioplegia system through a high-pressure stopcock that can connect to the Y-connection between the SVC and right atrial cannulas. Retrograde cerebral perfusion may be interrupted for variable periods of time during deep hypothermia as required by various surgical maneuvers. The temperature of the retrograde perfusate is maintained at 12 to 18°C. After completion of aortic arch anastomoses, air is removed from the aorta and graft by allowing it to fill by retrograde cerebral perfusion. After arch deairing, a cross-clamp is placed across the ascending aortic graft, and standard CPB with antegrade cerebral perfusion, that is, antegrade graft perfusion, is reinstituted for the final repair and rewarming. Our practice is to always reestablish antegrade flow via direct cannulation of the ascending graft using either a prefabricated 8- or 10-mm side-arm or by placing a pursestring suture in the graft and directly cannulating it.

Antegrade Cerebral Perfusion

Used routinely by many centers, antegrade cerebral perfusion is primarily beneficial over RCP in situations in which the expected circulatory arrest time is greater than 35 to 45 minutes. Common strategies include direct cannulation of the head vessels with balloon-tip catheters as described by Kazui or by right axillary cannulation.121 When performing direct arch vessel cannulation, it is advisable to use balloon tip catheters that have individual pressure-monitoring lines so the true perfusion pressures can be monitored to avoid cerebral hypertension. Right radial artery monitoring may also be helpful. Perfusion is typically performed at 10 cc/kg/min and mean pressures are maintained at 40 to 70 mm Hg. Perfusate temperature should approximate the core temperature. Optimal protection is gained by direct perfusion of all three arch branches, not just the left common carotid and innominate arteries.

Axillary cannulation is performed via cutdown to the right axillary artery with an 8- to 10-mm Dacron graft sewn in an end-to-side fashion (Fig. 51-22). The graft is ligated at the end of the procedure. Given the fragility of the axillary artery, few surgeons cannulate it directly. As with direct cerebral vessel perfusion, perfusion pressure is maintained at 10 cc/kg/min and mean pressures are 40 to 70 mm Hg. The innominate artery is either snared or clamped at its origin. Although antegrade cerebral perfusion via this method is rapid and effective, it only provides unilateral perfusion; contralateral ischemia may still occur. To maintain adequate cerebral perfusion pressure and eliminate the effect of arterial–arterial collaterals stealing flow, ideally the left common carotid and subclavian artery origins are controlled as well.122

Myocardial Protection

Typically, 1 L of cold blood hyperkalemic cardioplegia (4°C) is given antegrade into the aortic root. A left ventricular vent is employed to prevent distention. In cases of severe aortic insufficiency, the aorta is opened and the coronary ostia are cannulated directly with handheld cannula. A temperature probe is placed through the anterior myocardium into the septum and a myocardial temperature of 6 to 8°C is achieved. Retrograde cardioplegia is administered at least every 20 minutes and continuously when possible. It is important to give cardioplegia immediately before commencing circulatory arrest and at its conclusion.

Ascending Aortic Replacement

After the aortic cross-clamp is applied and cardioplegic arrest is achieved as described in the preceding, the ascending aorta is transected about 1 cm below the clamp and resected to the level of the sinotubular junction. The aorta is carefully freed from the pulmonary artery using low-energy electrocautery. Using a metric sizer, the diameter of the sinotubular junction that provides adequate leaflet coaptation is determined; this should be within 10% of the annular diameter. The aortic valve is inspected to ensure that it is trileaflet and free from significant calcification or leaflet pathology. If the aortic valve is to be replaced, this is performed at this point using standard techniques. An appropriate-size graft is then anastomosed to the sinotubular junction using a running 4-0 polypropylene. The external aspect may be reinforced with Teflon felt if the aorta appears especially thin and a root replacement is not feasible. In cases of acute dissection, individual pledgeted sutures are placed at upper aspects of the commissures to resuspend the aortic valve and Teflon felt is placed inside between the dissected layers to form a robust neomedia that can hold sutures.

Composite Root Replacement

Aortic root replacement involves excision of the entire ascending aorta to the native valve annulus with mobilization of coronary buttons and placement of a composite valve and polyester graft conduit into the annulus. After cross-clamping and administration of cardioplegia, the ascending aorta is resected to the level of the sinotubular junction. The sinuses are mobilized off of the pulmonary arteries and right ventricle and the coronary buttons are mobilized as described in the following. Unless a root reimplantation procedure is being performed, excessive proximal mobilization of the root is unnecessary.

The aortic valve leaflets are excised. The annular dimension is sized and an appropriately sized prosthesis is selected. Mechanical composite prostheses come prefabricated with either a polyester straight tube graft or artificial neosinuses created by changing the orientation of the polyester in the sinus segment. If a tissue valve is desired, a polyester graft that is either straight or has neo-sinuses is anastomosed with a running 3-0 or 4-0 polypropylene suture to an appropriately sized stented tissue valve. If using a Dacron graft with neo-sinuses, this should be sewn 3 to 4 mm below the start of the neo-sinus segment. The valve sutures must pass through both the valve sewing ring and the Dacron graft to ensure hemostasis.

The composite prosthesis may be placed with either pledgeted everting; that is, “intra-annular,” mattress sutures with pledgets on the outside of the annulus or in a “supra-annular” configuration with pledgets on the ventricular side of the annulus. Typically, the everting technique is used because it is hemostatic and strong. Implanting the root with pledgets on the ventricular side requires less mobilization of the sinuses, which may be advantageous in certain situations and may allow for a slightly larger prosthesis. When implanting a mechanical prosthesis, the everting technique is preferred because it is less prone to pannus formation, which may interfere with valve function. Care must be taken with either technique not to shorten the mitral valve anterior leaflet with excessively large bites with the annular sutures along the left and noncoronary sinuses. Polyester, braided 2-0 sutures with a larger needle than used for aortic valve replacement is employed.

Once the valve-conduit is tied down, the coronary buttons are anastomosed using 5-0 Prolene sutures as described in the following (Fig. 51-23). Pressurization of the new root by inserting a catheter into the proximal graft, running cardioplegia and clamping the graft distally after de-airing the neoroot allows assessment of all suture lines.

Implantation of stentless bioroots, homograft roots, pulmonary autografts, and valve-sparing procedures is discussed in previous chapters.

Distal Anastomosis

Distal reconstruction is performed as a clamped or open anastomosis. In aneurysm cases, open distal techniques that eliminate all diseased aorta and the weakened cross-clamp site are routinely employed. Circulatory arrest techniques as previously described are employed. Distal anastomoses are performed with a beveled polyester graft using a running 4-0 polypropylene suture. The distal anastomosis is performed as an “on-lay” type anastomosis with the graft invaginated into the distal aorta. This pushes the graft material into the native aorta when the aorta is pressurized and prevents leaks. In cases of extremely friable aorta, Teflon felt placed along the outer aspect may also be beneficial but does not substitute for a proper “on-lay” technique.

Management of Coronary Arteries

Mobilization of the coronary artery buttons in root operations remains the most technically demanding and least forgiving aspect of root operations. The left main button is mobilized after the aorta has been fully dissected from the pulmonary artery. It is frequently useful to work from the inside of the aorta outward, gently scoring the dissection plane with low-intensity electrocautery. Generally, 1 to 2 cm of freedom of motion in all directions is required for adequate mobilization. Care must be taken mobilizing the right coronary artery to ensure the right ventricle is not inadvertently entered. Application of retrograde and direct antegrade cardioplegia into the coronaries after mobilization will identify any small branch disruptions or major injuries while they are still repairable.

When anastomosing the left coronary button to the aortic graft, if a graft with premade sinuses of Valsalva is used, the button is typically sewn at or below the level of the equator of the sinus segment. The right coronary, which is more likely to kink as the right ventricle pushes it cephalad once the heart fills, is sewn at or above the level of the equator. When using a straight graft, some surgeons will determine the final position of the right coronary button after completing the graft-to-graft anastomosis, filling the heart and briefly removing the cross-clamp. When separating from bypass, if there are new gross wall motion abnormalities, coronary artery injury or kinking should be immediately suspected. Our preference in these situations is to immediately bypass the affected territory rather than attempt to salvage a friable coronary button. For a left-sided problem, a LIMA to LAD bypass will typically resolve the difficulty expediently.

In complex endocarditis, dissection, severe calcification, or reoperative cases, coronary artery buttons may be too damaged or immobile to directly attach to the graft. In such situations, a Cabrol-type coronary anastomosis, where the coronary os are anastomosed to an 8- to 10-mm Dacron grafts in a “moustache” configuration, may be employed (Fig. 51-24). Alternatively, segments of reversed saphenous vein can be used as interposition grafts. Typically these grafts are 3 to 5 cm in length, are anastomosed fairly high on the aortic graft, and follow a gentle S-shaped curve to prevent kinking. In cases of right coronary button problems, proximal ligation and bypass to the main right coronary artery is another alternative.

Aortic Wrapping and Reduction Aortoplasty

Reduction ascending aortoplasty and aortic wrapping are less common techniques to address ascending aortic aneurysms typically reserved for patients undergoing concomitant aortic valve replacement but who are deemed too high risk for either composite root or ascending aortic replacement or who have ascending aortic dimensions less than the recommendations for replacement as a prophylactic measure to prevent aneurysm formation. Reduction aortoplasty involves excision of a segment of the ascending aorta to achieve a normal radial maximal dimension. It may be performed either with a side-biting aortic clamp, cross-clamped or with open technique depending on the length of aortoplasty and technique used.123–125 The excised segment may be taken in the long axis of the aorta down to the sinotubular junction (true reduction annuloplasty), or lesser plication techniques may be employed. External reinforcement can also be performed in conjunction with reduction aortoplasty. Concerns regarding this technique include dehiscence or aortic rupture at the suture line, which is constantly under tension from the radial force on the aortic wall during systole.

Aortic wrapping of girdling is either performed by itself or in conjunction with reduction aortoplasty. Wrapping has been performed with cellophane, polyester grafts and meshes, PTFE, and other materials. Neri and colleagues described two patients required reoperation because of development of false aneurysms after aortic valve replacement with aortoplasty and wrapping.126 The unwrapped parts of the ascending aorta in both patients appeared normal; conversely, the aortic wall underlying the wrap was severely atrophic, a phenomenon previously reported with abdominal aneurysms that were wrapped without aortoplasty. In a larger series by Cohen and colleagues, among 102 patients who underwent aortic wrapping with a polyester mesh followed for a median of 4.7 years, there were no instances of major aortic complications and an average aneurysm growth of 2.6 mm over the follow-up period.127

Concomitant Mitral Surgery

Mitral valve disease is frequently encountered in patients with aortic aneurysms. This is particularly true for patients with Marfan's syndrome, in whom the incidence approaches 30%.128 Patients who have evidence of moderate to severe mitral regurgitation should undergo mitral valve repair at the time of aortic replacement. Gillinov and colleagues reported results of mitral valve repair in patients with Marfan's syndrome, many of whom also had simultaneous replacement of the aortic root.129 They observed an 88% actuarial rate of freedom from significant mitral regurgitation at 5 years. A fairly liberal approach to mitral valve intervention is warranted in aortic root replacement patients as reoperation for late mitral regurgitation may be particularly technically difficult. Additionally, care must be taken when taking the annular stitches along the aorto-mitral continuity to avoid shortening the anterior leaflet of the mitral valve.

Reoperative Considerations

Reoperative surgery on the ascending aorta and aortic root can be particularly challenging but is becoming more frequent in experienced centers. Increased use of tissue aortic valves in younger patients, biologic porcine or composite pericardial roots, and homografts in past few decades suggest that many patients may require reoperative root intervention. Additionally, root replacement may be required after the development of ascending aortic aneurysms in bicuspid patients who have previously undergone aortic valve replacement only. Indications for reoperation include aortic insufficiency, development of aneurysms or dissections in remaining segments of the thoracic aorta, false aneurysms, prosthetic valve dysfunction, infection or thrombosis, or degeneration of biologic prostheses.

Re-entry is usually accomplished with a repeat sternotomy incision, although for complex arch operations involving the proximal descending aorta, a thoracosternotomy approach may be required.130 In cases of massive ascending aortic aneurysm, adhesion of the aorta to the posterior table of the sternum or contained ruptures, exposure of alternative cannulation site such as the right axillary artery or femoral artery is necessary. Massive aortic hemorrhage upon sternal entry should by locally controlled by forcibly reapproximating the sternum, heparinizing the patient, instituting peripheral cardiopulmonary bypass, and cooling to deep hypothermia such that the sternal reentry can be completed under lower flow conditions with active pump-suction in the operative field. If entering the aorta on re-entry is felt to be inevitable, staring cardiopulmonary bypass and cooling before sternotomy may be a superior strategy. In cases of moderate to severe aortic insufficiency, venting of the left ventricle prior to cardiac fibrillation is mandatory and can be accomplished by a small left anterior thoracotomy incision and direct venting of the apex.

Cross-clamping in the reoperative scenario may also be hazardous as previous graft material may cause severe adhesions to the pulmonary artery making the dissection of a clamping site difficult. Previous use of a porcine root prosthesis or left-sided bypass grafts makes this dissection particularly difficult. If the pulmonary artery is inadvertently entered, patching with a pericardial substitute is usually necessary.

Mobilization of the coronary arteries is frequently difficult and creation of a Cabrol-type anastomosis, interposition grafts, or bypass grafts are frequently necessary. Previous coronary bypass grafts should be reimplanted, and frequently, interposition vein grafts are required to accomplish this. Direct cardioplegia administration down bypass grafts is preferred but avoided when there is diffuse vein graft disease.131 Retrograde cardioplegia is extremely helpful in this circumstance.

In cases of reoperation for failed porcine bioroots, root replacement is preferable to simple aortic valve implantation within the porcine root because there is a higher likelihood for valve dehiscence owing to the degenerative nature of the root tissue.132 If aortic valve implantation into a porcine root is being performed, all of the aortic valve implantation sutures must traverse the native aortic root tissue, not just the porcine tissue.

Hybrid and Stent Graft Approaches

Advances in the design of highly flexible and low-profile thoracic aortic stent grafts have generated an interest in using these devices for the ascending aorta in patients who are otherwise not reasonable risk surgical candidates. Essential design requirements for ascending aortic stent grafts include a high degree of flexibility and conformability, short graft lengths, no exposed bare metal, and long delivery systems, because most TEVAR delivery systems will not reach the proximal ascending aorta from the femoral artery. Alternative approaches for access sites for the stent graft include axillary artery, carotid artery, and perhaps most promising, transapical artery. Graft lengths are more critical in the ascending aorta than in the thoracic aorta as the distance between sinotubular junction and/or coronary ostia and the takeoff of the innominate artery is typically shorter than 10 cm, and is therefore shorter than most thoracic devices. The antegrade transapical technique may also offer potential advantage by limiting the distance between the sheath and the device, thereby minimizing the potential for device migration during deployment, as is seen in transapical deployment of transcatheter aortic valves. Stent graft placement has been described to treat focal ascending aneurysms in nonoperative candidates (Fig. 51-25).133

Bleeding

Woven Dacron grafts impregnated with collagen or gelatin are relatively impervious to blood and have reduced blood loss following replacement of the ascending aorta compared with knitted grafts. Precise suturing with careful attention to avoid torque on the suture needles while constructing anastomoses is critical to avoid the inevitable needle-hole bleeding at the end of the surgery. Tension must be avoided at the sites of coronary reimplantation, because this is a frequent site of bleeding. The modified Cabrol method or an interposition graft should be used when any tension is present. The inclusion technique of graft insertion is associated with an increased incidence of bleeding and pseudoaneurysm formation and has largely been abandoned. In very friable aortas, Teflon felt may be used to reinforce the suture line on the outside of the anastomosis in which a thin strip of felt is slipped into the suture line as it is tightened. Alternatively, it may be sewn to the inside, outside or both sides of the native aorta with a running polypropylene stitch before sewing the graft.

In cases of refractory coagulopathy, the anastomosis can be wrapped tightly with a small segment of polyester graft or Teflon felt to reduce tension on the suture line and reduce needle hole bleeding (Fig. 51-26). Blood transfusion can be avoided in a significant number of patients with the use of blood conservation techniques such as Cell Savers, autologous blood donation, plateletpheresis, the reinfusion of chest tube drainage, and the use of antifibrinolytics such as aminocaproic acid and tranexamic acid. Since the removal of the antifibrinolytic agent aprotinin from the market because of concerns regarding renal dysfunction and mortality, bleeding has anecdotally become more common. Activated human recombinant factor VII may be helpful as a last resort when treating refractory bleeding that does not respond to any other therapies, although this may induce unanticipated thrombosis in arterial structures.134

In cases of ongoing postoperative hemorrhage, expedient return to the operating room for reexploration is preferable to massive transfusion or tamponade. Postoperative bleeding requiring reexploration ranges from 2.4 to 11.1%.135,136

Stroke

Neurologic injury after proximal aortic surgery remains a significant cause of morbidity and mortality. Embolization of atherosclerotic debris or thrombus from the ascending aorta and arch produces focal neurologic deficits. Diffuse injury can be attributed to microemboli of air or cellular debris, insufficient or uneven cooling, and a prolonged circulatory arrest period. After circulatory arrest periods exceeding 40 minutes the incidence of stroke greatly increases.137 Profound hypothermia may itself be injurious to the central nervous system without associated circulatory arrest.138

Stroke owing to embolization is diminished when the aorta is evaluated via epiaortic ultrasound or other imaging modality to detect atherosclerotic plaques and thrombus.139 This allows appropriate adjustments to be made in clamping and cannulation strategies. Resumption of antegrade circulation through the graft once the distal aortic anastomosis is complete, rather than retrograde via the femoral vessels, after a period of circulatory arrest avoids embolization of distal aortic debris. Patients with severe carotid artery occlusive disease are at increased risk of stroke during ascending aortic procedures, and patients older than 65, those with peripheral vascular disease, or those with pertinent histories should be evaluated.140

Patients with new postoperative strokes should be rapidly evaluated by the consultant neurology service and undergo early brain imaging. New embolic events should be managed aggressively with induced hypertension once intracranial hemorrhage has been ruled out.

Pulmonary Dysfunction

Cardiopulmonary bypass is known to cause alterations in pulmonary function as evidenced by changes in alveolar–arterial oxygen gradients, pulmonary vascular resistance, pulmonary compliance, and intrapulmonary shunting. Usually these changes are subclinical, but a full-blown adult respiratory distress–like syndrome is reported in 0.5 to 1.7% of patients following cardiopulmonary bypass.141–143 The specific cause is the subject of much investigation and debate, but it is generally accepted that exposure of blood elements to the foreign surface of the cardiopulmonary circuit results in the activation of inflammatory cells and the complement cascade resulting in pulmonary injury.144 The duration of cardiopulmonary bypass, urgency of the procedure, and general condition of the patient may roughly correlate with the occurrence and severity of pulmonary dysfunction, but it can be unpredictable.

Treatment is supportive, with early diagnosis and treatment of any subsequent pulmonary infections. Ten to eighteen percent of patients require prolonged mechanical ventilation. Preventive measures may include preoperative optimization of pulmonary function, minimization of pump time, judicious use of blood products, heparin-coated bypass circuits, and leukocyte depletion.145

Myocardial Dysfunction

Transient myocardial dysfunction following complex aortic surgery requiring inotropic support is common with 18 to 25% of patients requiring more than 6 hours of inotropic support.146,147 Meticulous attention should be paid to integrated myocardial protection with cold-blood cardioplegia administered frequently in antegrade and retrograde fashions. This is particularly important in patients with significant left ventricular dilatation seen with aortic insufficiency or hypertrophy seen with aortic stenosis. Maintenance of high-perfusion pressures after removal of cross-clamp optimizes myocardial perfusion during the critical reperfusion period. Optimization of right ventricular function with afterload reducing agents such as milrinone or inhaled prostaglandins while weaning from cardiopulmonary bypass is vital for maintaining adequate left ventricular filling in cases of severe diastolic dysfunction or ventricular hypertrophy. Postoperative myocardial infarction, reported in up to 2.5% of cases, may be related to technical problems with coronary reimplantation.148

Perioperative Mortality

Contemporary surgical series on ascending aortic disease using modern grafting techniques and methods of cerebral and myocardial protection report hospital mortality rates of 1.7 to 17.1%.148–152 Comparison of outcomes is difficult, however, because of heterogeneity of patients. Some series do not include dissection, and the proportion of emergent operations, reoperations, and arch replacements is highly variable. The common causes of early death are cardiac failure, stroke, bleeding, and pulmonary insufficiency.148,149

Emergent operation after the onset of acute dissection or rupture is the highest risk factor for early death. Risk of death following elective intervention is increased by increasing New York Heart Association classification, increasing age, prolonged cardiopulmonary bypass time, dissection, previous cardiac surgery, and need for concomitant coronary revascularization.151,152

Late Mortality

Reported actuarial survival, like early mortality, is variable and dependent on the patient cohort. Survival rates are 81 to 95% at 1 year, 73 to 92% at 5 years, 60 to 73% at 8 to 10 years, and 48 to 67% at 12 to 14 years.153–156 Predictors of late mortality include elevated New York Heart Association class, requirement for arch reconstruction, Marfan's syndrome, and extent of distal disease.157–160 The most common cause of late death is cardiac, but distal aortic disease accounted for 32% of late deaths in one series.161

Reoperation

Reoperations occur because of pseudoaneurysm formation, valve thrombosis, endocarditis or graft infection, progression of disease in the native valve or remaining aortic segments, or degeneration of a bioprosthesis. Reported mortality for reoperative ascending aortic surgery varies between 4 and 22%.162,163

Freedom from reoperation is 86 to 90% at 9 to 10 years (Fig. 51-27).164,165 Predictors of late reoperation have included Marfan's syndrome, the inclusion cylinder technique, and chronic dissection.166 Surveillance of patients who have undergone previous aortic surgery to minimize the need for urgent reoperations and appropriate resection of all diseased aortic tissue at the time of original operation improves outcomes. Up to 60% of reoperations occur because of inadequate repair during the initial operation.167 This is owing to failure to resect the most distal aspects of aneurysmal disease by performing a clamped distal anastomosis or failure to adequately address root pathology with full root replacement. Previous inclusion-type anastomotic techniques were associated with higher rates of early reoperation owing to pseudoaneurysm formation (Fig. 51-28).168

Marfan's syndrome patients are particularly prone to requiring reoperation (Fig. 51-29).169 Gott and colleagues reviewed the experience with root replacement at 10 surgical centers in 675 Marfan patients between 1968 to 1996.170 The 30-day mortality was 3.3%, but was only 1.5% for elective repair. Emergency surgery resulted in a 30-day mortality of nearly 12%. The survival rate was 93% at 1 year, 84% at 5 years, 75% at 10 years, and 59% at 20 years (Fig. 51-30). Complications related to the residual thoracic aorta and arrhythmias were the leading causes of death. The most frequent late complication was thromboembolism. Advanced New York Heart Association class at the time of original operation was the only predictor of late death.

Graft Infection

Graft infections are reported in up to 0.9 to 6% of patients following surgery of the thoracic aorta and are associated with a very high (25 to 75%) mortality rate.171–173 Most graft infections occur in the first month after operation and are frequently associated with wound infections. They may occur years later in cases of associated valve endocarditis or bacteremia from indwelling catheters or other systemic infections. The major infectious agents are S. aureus, S. epidermidis, and Pseudomonas.174 The ascending aortic graft may be particularly vulnerable because of proximity to the wound and poor natural tissue coverage. For this reason, full coverage of the ascending graft material with the pericardial fat pad is advisable in all cases. This serves to isolate the graft from the sternum if it becomes infected.

Patients frequently present with persistent fevers and elevated white cell count. CT or MRI may demonstrate air or fluid collections around the graft. There may be associated pseudoaneurysms, fistula, anastomotic leak, hemolysis, and embolism. Nuclear imaging techniques may be helpful but can be nonspecific for infection versus normal postoperative inflammation.175 TEE may show valvular vegetations or abscesses.

Ideally, treatment of the stable patient begins with intravenous antibiotics to control septicemia and often clear blood cultures before reoperation. In extremely high-risk patients, in whom reoperative mortality is prohibitive, lifelong suppressive antibiotics may be acceptable. Surgical treatment of infected ascending aortic grafts, as described by Hargrove and Edmunds, includes removal of all infected prosthetic material, aggressive tissue debridement, local irrigation, systemic antibiotic therapy, replacement of the infected conduit, and use of autologous tissue to surround the graft and obliterate dead space.176 Aortic homograft may potentially be more resistant to repeat infection. Greater omentum may be also brought up through the diaphragm as a vascularized pedicle to wrap around the aortic graft and isolate it from the sternum. Concomitant sternal infections should be managed with aggressive debridement, sterilization with vacuum-assisted wound drainage, and delayed flap reconstruction. In severe cases, open continuous antibiotic wound irrigation for several days can assist in clearing the infection.177 Long-term antibiotics should be continued intravenously for at least 6 weeks and suppressive oral antibiotics may be indicated over the long term thereafter.