Surgical removal of the chronic thromboembolic material remains the only curative option for patients with CTEPH. In an experienced center, the procedure can be performed with low operative morbidity and mortality, and can produce tremendous hemodynamic benefit with excellent prognoses. The only other surgical alternative for these patients is transplantation. However, as mentioned earlier, the authors consider transplantation inappropriate for treatment of this disease and believe it to be obsolete in the management of patients with CTEPH. In light of the mortality and morbidity rates of patients on transplant waiting lists, the higher risk of the operation, and the less desirable or inferior survival rate (approximately 80 percent at 1 year at experienced centers for transplantation vs 95 percent for PEA), PEA is clearly the superior choice. Furthermore, PEA appears to be permanently curative, and the issues of a continuing risk of rejection and immunosuppression are not present.
Allison performed the first successful pulmonary “thromboendarterectomy” through a sternotomy, using surface hypothermia in 1960, but only fresh clots were removed.25 This operation took place 12 days after a thigh injury that led to PE, and an endarterectomy was not performed. Since then, there have been reports of the surgical treatment of chronic pulmonary thromboembolism, but most of the surgical experience in PEA has been reported from the UCSD Medical Center. Braunwald commenced the UCSD experience with this operation in 1970, which now totals almost 2600 cases. The operation described below, using deep hypothermia and circulatory arrest, is now our standard procedure.
Guiding Principles of the Operation
Once the diagnosis of thromboembolic pulmonary hypertension has been established firmly, the decision for operation is made based on the severity of symptoms and the general condition of the patient. In general, suitable candidates with CTEPH enjoy excellent hemodynamic results, with outstanding long-term prognoses. Early in the PEA experience, Moser and colleagues pointed out that there were three major reasons for considering endarterectomy: hemodynamic, alveolo-respiratory, and prophylactic.
The hemodynamic goal is to prevent or ameliorate right ventricular compromise caused by pulmonary hypertension. The respiratory objective is to improve respiratory function with the removal of a large ventilated but unperfused physiologic dead space. The prophylactic goal is to prevent progressive right ventricular dysfunction or retrograde extension of the obstruction, which might result in further cardiorespiratory deterioration or death. The authors’ experience has added another prophylactic goal: the prevention of secondary arteriopathic changes in the remaining patent vessels.
Although the essential techniques of PEA are quite similar to other open-heart operations, several guiding principles are specific for this procedure. For pulmonary hypertension to be a major factor, both pulmonary arteries must be involved substantially. The surgery is therefore always bilateral, although the volume of chronic thromboembolic material may vary significantly between the two lungs. The only reasonable approach to both pulmonary arteries is through a median sternotomy incision. Historically, there were many reports of a unilateral operation, and occasionally this is still performed in inexperienced centers through a thoracotomy. However, the unilateral approach ignores the disease on the contralateral side, subjects the patient to hemodynamic jeopardy during the clamping of the pulmonary artery, and does not allow for good visibility because of the continued presence of bronchial blood flow. In addition, collateral channels develop in chronic thrombotic hypertension not only through the bronchial arteries but also from diaphragmatic, intercostal, and pleural vessels. The dissection of the lung in the pleural space via a thoracotomy incision therefore can be extremely bloody. The median sternotomy incision, apart from providing bilateral access, avoids entry into the pleural cavities and permits the ready institution of cardiopulmonary bypass.
A thorough and successful endarterectomy of the pulmonary arteries can only be performed in a bloodless field and under circulatory arrest. Cardiopulmonary bypass is therefore essential not only to ensure cardiovascular stability when the operation is performed, but also to allow cooling of the patient for periods of circulatory arrest. Exceptional visibility of the pulmonary vasculature is required, and a bloodless field is an absolute requirement to define an adequate endarterectomy plane and to then follow the PEA specimen deep into the subsegmental vessels. Because of the copious bronchial blood flow usually present in these cases, periods of circulatory arrest are necessary to ensure perfect visibility. Again, there have been sporadic reports of the performance of this operation without circulatory arrest. However, it should be emphasized that although endarterectomy is possible without circulatory arrest, a complete and full endarterectomy is not. Without a complete endarterectomy all the way to the distal tail ends of each branch, successful hemodynamic improvement is not achievable, leaving the patients with residual pulmonary hypertension and a subsequent poor prognosis in the short- and long terms.
The authors always initiate the procedure without circulatory arrest; depending on the collateral flow, a variable amount of dissection is possible before the circulation is stopped, but never complete dissection. The circulatory arrest periods are limited to 20 min, with restoration of flow after each arrest. With experience, the endarterectomy is generally performed with a single period of circulatory arrest on each side.
A true endarterectomy in the plane of the media must be accomplished. It is essential to appreciate that the removal of visible thrombus is largely incidental to this operation. Indeed, in most patients, no free thrombus is present, and on initial direct examination, the pulmonary vascular bed may appear normal to an inexperienced eye. The early literature on this procedure is filled with reports of thrombectomy performed without a complete endarterectomy, and in these cases the pulmonary artery pressures did not improve, often with the resultant death of the patient.
After a median sternotomy is performed, the pericardium is incised longitudinally and attached to the wound edges. Typically the right heart is enlarged, with a tense right atrium and a variable degree of tricuspid regurgitation. There is usually severe right ventricular hypertrophy. These patients are generally quite sensitive to any manipulation of the heart; with critical degrees of obstruction, the patient’s condition may become quite unstable.
Anticoagulation is achieved with the use of beef-lung heparin sodium (400 units/kg, intravenously) administered to prolong the activated clotting time beyond 400 s. Full cardiopulmonary bypass is instituted with high ascending aortic cannulation and bicaval cannulation. The cannulae must be inserted into the superior and inferior vena cavae sufficiently to enable subsequent opening of the right atrium. The heart is emptied on bypass, and a vent is placed in the midline of the main pulmonary artery 1 cm distal to the pulmonary valve. This point can also be used to mark the beginning of the left pulmonary arteriotomy.
When cardiopulmonary bypass is initiated, surface cooling with both a head jacket and cooling blanket is begun. Cooling generally takes 45 min to 1 h. When ventricular fibrillation occurs, an additional vent is placed in the left atrium through the right superior pulmonary vein. This prevents atrial and ventricular distension from the large amount of bronchial arterial blood flow that is common in these patients.
The primary surgeon starts the operation on the patient’s left side. During the cooling period, some preliminary dissection can be performed, with full mobilization of the right pulmonary artery from the ascending aorta. The superior vena cava is also fully mobilized. The approach to the right pulmonary artery is made medial, not lateral, to the superior vena cava. All dissection of the pulmonary arteries takes place intrapericardially, and neither pleural cavity should be entered. An incision is then made in the right pulmonary artery from beneath the ascending aorta out under the superior vena cava and entering the lower lobe branch of the pulmonary artery just after the take-off of the middle lobe artery (Fig. 45-4). It is important that the incision stays in the center of the vessel and continues into the lower, rather than the middle lobe artery.
Exposure of the right pulmonary artery. The incision is placed between the superior vena cava (SVC) and the aorta (as shown in the insert). It is imperative that the incision toward the right lower lobe artery is made in the middle of the vessel.
A modified cerebellar retractor is placed between the aorta and superior vena cava. Upon opening the pulmonary artery a varying degree of loose thrombus may be present. This material is then removed to ensure good visualization of the vascular bed. It is most important to recognize that (1) an embolectomy without subsequent endarterectomy is quite ineffective, regardless of the amount of thromboembolic material, and (2) in most patients with chronic thromboembolic hypertension, direct examination of the pulmonary vascular bed at operation generally reveals no obvious embolic material. Therefore, to the inexperienced or cursory glance, the pulmonary vascular bed may well appear normal even in patients with severe chronic embolic pulmonary hypertension.
When the patient’s temperature reaches 20°C, the aorta is cross-clamped and a single dose of cold cardioplegic solution (I L) is administered. Additional myocardial protection is obtained with the use of a cooling jacket. The entire procedure is now performed with a single aortic cross-clamp period with no further administration of cardioplegic solution.
If the bronchial circulation is not excessive, the endarterectomy plane can be found during this early dissection. However, although a small amount of dissection can be performed before the initiation of circulatory arrest, it is unwise to proceed unless perfect visibility is obtained because the development of a correct plane is essential. Recognizing the plane is perhaps the most crucial and technically challenging part of the operation.
When blood obscures direct vision of the pulmonary vascular bed, thiopental is administered (500 mg to 1 g) until the electroencephalogram (EEG) becomes isoelectric. In most cases, the EEG is already isoelectric once the core temperature reaches 20°C. Circulatory arrest is then initiated, and the patient is exsanguinated. All monitoring lines to the patient are turned off to prevent the aspiration of air. Snares are tightened around the cannulae in the superior and inferior vena cavae.
A microtome knife is used to develop the endarterectomy plane posteriorly, because any inadvertent egress in this site could be repaired readily, or simply left alone. Dissection in the correct plane is critical because if the plane is too deep, the pulmonary artery may perforate, with fatal results. If the dissection plane is not deep enough, inadequate amounts of the chronic thromboembolic material will be removed, leaving the patient with residual pulmonary hypertension.
Once the plane is correctly developed, a full-thickness layer is left in the region of the incision to ease subsequent repair. The endarterectomy is then performed with an eversion technique. Because the vessel is everted and subsegmental branches are being worked on, a perforation here will become inaccessible later. This is why the absolute visualization in a completely bloodless field provided by circulatory arrest is essential. It is important that each subsegmental branch is followed and freed individually until it ends in a “tail,” beyond which there is no further obstruction. Residual material never should be cut free; the entire specimen should “tail off” and come free spontaneously. Although retrograde cerebral perfusion has been advocated for total circulatory arrest in other procedures, it is not helpful in this operation because it does not provide for a completely bloodless field. Furthermore, with the short arrest times that can be achieved with experience, it is not necessary.
Once the right-sided endarterectomy is completed, circulation is restarted, and the arteriotomy is repaired with a continuous 6-0 polypropylene suture. The hemostatic nature of this closure is aided by the nature of the initial dissection, with the full thickness of the pulmonary artery being preserved immediately adjacent to the incision.
After completion of the repair of the right arteriotomy, the surgeon moves to the patient’s right side. The pulmonary vent catheter is withdrawn, and an arteriotomy is made in the left pulmonary artery lateral to the pericardial reflection, avoiding entry into the left pleural space. Additional lateral dissection does not enhance intraluminal visibility, may endanger the left phrenic nerve, and makes subsequent repair of the left pulmonary artery more difficult (Fig. 45-5). The left-sided dissection is virtually analogous in all respects to that accomplished on the right. The duration of circulatory arrest intervals during the performance of the left-sided dissection is subject to the same restriction as for the right.
Exposure of the left pulmonary artery with its corresponding incision. Note that the incision begins in the mid portion of the main pulmonary artery at the site of the insertion of the pulmonary artery vent.
After completion of the endarterectomy, cardiopulmonary bypass is reinstituted and warming is commenced. The rewarming period generally takes approximately 90 min but varies according to the body mass of the patient.
The pulmonary artery is then closed and the pulmonary arterial vent is replaced. The right atrium is then opened and examined. Any interatrial communication is closed. Although tricuspid valve regurgitation is invariable in these patients and is often severe, tricuspid valve repair is not performed. Right ventricular remodeling occurs within a few days, with the return of tricuspid competence. If other cardiac procedures are required, such as coronary artery bypass or mitral or aortic valve surgery, these are performed conveniently during the systemic rewarming period. Myocardial cooling is discontinued once all cardiac procedures have been concluded. The left atrial vent is removed, and the vent site is repaired. All air is removed from the heart and the aortic cross-clamp is removed.
When the patient has rewarmed, cardiopulmonary bypass is discontinued. Dopamine hydrochloride is routinely administered at renal doses, and other inotropic agents and vasodilators are titrated as necessary to sustain acceptable hemodynamics. The cardiac output is generally high, with a low systemic vascular resistance. Temporary atrial and ventricular epicardial pacing wires are placed.
Despite the duration of extracorporeal circulation, hemostasis is readily achieved, and the administration of platelets or coagulation factors is generally unnecessary. Wound closure is routine. A vigorous diuresis is usual for the next few hours, often a result of the previous systemic hypothermia.