Pulmonary Thromboendarterectomy: Patient Selection, Techniques, Outcomes, and Recent Advances
Chronic ThromboEmbolic Pulmonary Hypertension (CTEPH) is a potentially curative form of pulmonary hypertension, which continues to be underdiagnosed. Pulmonary ThromboEndarterectomy (PTE, also referred to as PEA for Pulmonary Endarterectomy) is a technically challenging procedure that requires careful patient selection, meticulous surgical techniques, and expertise in postoperative care. Over the last decade, there have been significant advances not only in the techniques of the operation, but also in the postoperative management of major complications. Furthermore, advances have been made not only in medical therapy, but also in percutaneous interventions, in the form of balloon pulmonary angioplasty (BPA). BPA and medical therapy are considered to be palliative; they are reserved for patients who are inoperable, or for those who continue to have symptomatic PH postoperatively. PTE remains the gold standard treatment for CTEPH, as long as the patient has evidence of surgically accessible disease, and the patient has acceptable surgical risk. All CTEPH patients should be evaluated and considered for surgery, and no patient should be turned down without consultation with a multidisciplinary team at an expert center. Furthermore, no amount of PH or degree of right heart failure is a contraindication to surgery, as long as there is corresponding level of disease. Excellent short- and long-term results can be achieved with current data suggesting significant advantage with 10-yr survival of 85–90%.
INTRODUCTION
Pulmonary thromboendarterectomy (PTE) is the treatment of choice for patients with operable chronic thromboembolic pulmonary hypertension (CTEPH), as it is potentially curative. In expert centers that conduct > 50 PTE procedures per year, peri- and postsurgical mortality rates are very low and long-term outcomes are excellent, with 3-year postoperative survival of > 80%.1 Therapeutic decisions in CTEPH are based largely on the location of the arterial obstruction, with PTE for obstructions in main, lobar, and segmental vessels, and even for some subsegmental disease at expert centers, and balloon pulmonary angioplasty (BPA) and medical therapy for more distal or microvascular disease, respectively. Medical therapy and BPA are also options for patients with persistent or recurrent pulmonary hypertension (PH) after PTE. With increasing surgical experience and improvements in instruments and procedures, an increasing number of patients are now considered operable who would previously have been inoperable, including some patients with subsegmental disease. At the University of California, San Diego (UCSD), around 200 PTE procedures are performed every year and several advances have been developed, including resection of more distal disease, availability of PTE to patients previously considered to be too high risk for surgery, improved management of post-PTE complications, and minimally invasive PTE.2,3
While PTE can be combined with other treatment modalities, such as combination PTE and BPA, medical therapy for persistent or recurrent PH after PTE, and bridging therapy with medical therapy or BPA before surgery, data are generally limited. Combination treatment should therefore be considered on an individual patient basis. Though the majority of patients will have significant benefit from surgery and may not need additional treatment, some patients may require multimodal therapy with PTE, BPA, and/or medical therapy.
It is imperative to emphasize that for patients with surgically accessible disease, PTE is preferred and the standard of care, as it is potentially curative. For patients with inoperable CTEPH, as determined by an expert multidisciplinary team, percutaneous treatment with BPA is an emerging option, and the soluble guanylate cyclase stimulator, riociguat, is licensed for the treatment of patients with inoperable CTEPH and those with persistent or recurrent CTEPH after PTE.4 In addition, other pulmonary arterial hypertension–specific medical therapies (endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and proteinoids) are widely used off label to treat CTEPH. Regardless of operability status and choice of therapy, all patients with CTEPH should receive lifelong anticoagulation.
It is estimated that 1 to 1.36 PTE operations per million population are performed annually in the United States and around 1.7 per million population in Europe, representing a steady increase over the past decade as surgical expertise has improved and the number of expert centers has increased worldwide.5–7 What follows is a discussion around the role of PTE in the management of CTEPH, with a focus on our experience at UCSD.
OPERABILTY ASSESSMENT
PTE is the treatment of choice for CTEPH, and surgical mortality rates are low, particularly in large volume PTE centers.5 The proportion of patients with CTEPH considered inoperable has varied from 10% to 50%.1,5 Reasons for inoperability include the presence of distal pulmonary artery obstructions not accessible to surgery, imbalance between increased pulmonary vascular resistance (PVR) and the number of accessible occlusions (which suggests the presence of microvascular disease), and old age or comorbid conditions that make the patient unsuitable for surgery. Elevated PVR (> 1500 dyn · s · cm−5) alone is not a contraindication to surgery; in fact there is no higher limit of PVR that may make a patient inoperable, as long as there is a corresponding degree of obstructive disease. In some patients, severely elevated PVR in combination with other risk factors may render a patient inoperable. Furthermore, some patients with operable disease choose not to undergo surgery. Experience suggests that the number of patients considered inoperable may be overestimated due to some patients being incorrectly diagnosed as having CTEPH. Treatment guidelines recommend that patients with suspected CTEPH be referred to expert centers for confirmation of diagnosis and treatment, including PTE.5–10
An expert center is defined as one with a high annual volume of PTE procedures (> 50/y), surgical mortality < 5%, and the ability to perform segmental endarterectomy.9 In addition, expert centers should be capable of evaluating the need for other established treatment modalities and offering any that are deemed necessary.1 All expert centers must be able to call on a multidisciplinary team for evaluation and management of CTEPH, including a surgeon experienced with PTE, a PH specialist, a BPA interventionist, and a CTEPH-trained radiologist.1 It should be noted that some patients initially considered inoperable go on to have surgery after a second opinion at an expert center.5,9,10
Ultimately, therapeutic decisions in CTEPH are made according to the location of the arterial obstruction, with PTE for obstructions in larger vessels, BPA when the obstruction is in smaller vessels inaccessible to PTE, and medical therapy for obstructions not amenable to either intervention (Figure 1). As surgeons gain more experience with PTE and instruments and procedures improve, the distal limits of operability are becoming redefined, leading to a greater percentage of patients being considered operable.11–13
Citation: Advances in Pulmonary Hypertension 21, 3; 10.21693/1933-088X-21.3.73
For example, data from > 300 PTE operations at an Italian expert center showed similar in-hospital mortality in patients with distal disease as in those with more proximal disease, with significant, sustained improvements in hemodynamic, echocardiographic, and functional parameters.13 PTE also plays a role in the management of chronic thromboembolic disease (CTED), a condition in which pulmonary thromboembolic occlusions are present without PH at rest, but with similar symptoms to CTEPH. Data on PTE in patients with CTED are limited, although small-scale studies (n = 23–42) have shown hemodynamic and clinical improvements, with 1-year survival of 95% and improvements in quality of life.14–16
Around 200 PTE operations are conducted at UCSD annually, where multidisciplinary teams for management of CTEPH consist of a PTE surgeons, pulmonary vascular medicine specialists, interventional cardiologists, and imaging specialists. Diagnosis of CTEPH is confirmed using ventilation-perfusion scanning, and anatomical correlation is further investigated by computed tomography pulmonary angiography, as well as conventional pulmonary angiography. Patient selection for PTE is based on severity of CTEPH symptoms, degree of PH, right heart dysfunction, extent and level of obstruction, correlation of severity of PH and degree of obstruction, comorbidities, degree of difficulty, risk-benefit ratio, and the patients expectation of surgery and associated risks.17
As recommended by various guidelines, once the diagnosis of CTEPH is made, patients should be considered for surgery. No patient should be turned down without consultation from a multidisciplinary team at an expert center. As with any procedure, the success of PTE owes as much to appropriate patient selection as it does to surgical technique and postoperative management. In addition to determination of surgical accessibility, 2 other key components contribute to the determination of operability. Perhaps the most important determination is the correlation between the degree of hemodynamic impairment with the degree of disease burden as evidenced by imaging studies. This becomes a crucial determination, as there is no degree of hemodynamic impairment and no degree of PH to make a patient inoperable, as long as there is corresponding obstructive disease. These patients will tolerate the procedure well and enjoy excellent short- and long-term outcomes, as long as there is corresponding clot burden, and a full, thorough endarterectomy has been performed. The last component of the operability assessment relates to the patient’s underlying condition and comorbidities. Like any other major surgical procedure, PTE is individually based and heavily dependent on the surgeon’s and the center’s experience.
Correlating clot burden with hemodynamic impairment can be difficult. This is particularly true for patients with segmental and subsegmental level disease and advanced right heart failure. When considering operability, the goal is to identify adequate surgically accessible disease so that a relatively normal postoperative PVR can be predicted.
SURGICAL TECHNIQUE
There are several guiding principles that are specific to PTE. These include an approach that provides excellent exposure of the pulmonary vasculature, cardiopulmonary bypass with profound hypothermia and periods of circulatory arrest to achieve a bloodless field, and a complete bilateral endarterectomy in the correct plane.18,19 The operation is typically performed via median sternotomy. Some experienced centers have performed this procedure utilizing minimally invasive techniques2,3; however, the median sternotomy approach will be described here.
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 typically sensitive to manipulation of the heart and can become quite unstable.
After full heparinization (activated clotting time > 400 seconds), full cardiopulmonary bypass is instituted with high ascending aortic cannulation and bicaval cannulation. Once the heart is emptied on bypass, a vent is placed in the midline of the main pulmonary artery 1 cm distal to the pulmonary valve and directed into the right pulmonary artery. In addition to blood cooling via the heater-cooler, surface cooling with both a head ice-jacket and a cooling blanket is initiated at this time. Cooling typically takes about 45 minutes to an hour. Once ventricular fibrillation occurs, an additional vent is placed in the left ventricle via the right superior pulmonary vein (Figure 2).
Citation: Advances in Pulmonary Hypertension 21, 3; 10.21693/1933-088X-21.3.73
The primary surgeon starts the operation on the patient’s left side. The superior vena cava is fully mobilized, and right pulmonary artery dissected (Figure 3). 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.
Citation: Advances in Pulmonary Hypertension 21, 3; 10.21693/1933-088X-21.3.73
When the patient’s temperature reaches 20°C, the aorta is cross-clamped and cold cardioplegic solution (1 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.
A modified cerebellar retractor or Madani PTE retractor is placed between the aorta and superior vena cava. Upon opening the pulmonary artery, loose thromboembolic material is removed, and plane of dissection is identified. Recognizing the plane is the most crucial and technically challenging part of the operation. It is important to recognize that (1) an embolectomy without endarterectomy is ineffective, and (2) in most patients with CTEPH, the initial glance at the pulmonary vascular bed may appear normal, even with severe disease.
When blood obscures direct vision of the pulmonary vascular bed, circulatory arrest is 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.
An experienced surgeon will notice some subtle and some obvious signs of CTEPH. Figure 4 is a picture of intraoperative findings during right pulmonary endarterectomy, showing some obvious signs of obstructive disease.
Citation: Advances in Pulmonary Hypertension 21, 3; 10.21693/1933-088X-21.3.73
One must be very careful when starting the dissection plane, because if it is not deep enough, inadequate amounts of the chronic thromboembolic material will be removed, leaving the patient with residual PH. Too deep of a plane may result in pulmonary vessel perforation, with catastrophic and possibly fatal complications. Identification of the correct plane can be the most challenging part of this operation, in particular when segmental and subsegmental endarterectomies are being performed. The endarterectomy is then performed with an eversion technique and carried out to subsegmental branches. 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.
Once the right-sided endarterectomy is completed, circulation is restarted, and the arteriotomy is repaired with a continuous 6-0 polypropylene suture. After completion of the repair of the right arteriotomy, the surgeon moves to the patient’s right side. The pulmonary vent catheter is withdrawn, a heart net is used to retract the heart up, and an arteriotomy is made in the middle of 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. The left-sided dissection is virtually analogous in all respects to that accomplished on the right.
After completion of the endarterectomy, cardiopulmonary bypass is reinstituted and warming is commenced. The rewarming period generally takes approximately 90 minutes, but varies according to the body mass of the patient.
The pulmonary artery is then closed, and the pulmonary arterial vent is replaced. If there is any evidence of patent foramen ovale, atrial septal defect, or right atrial clot formation, the right atrium is then opened. Any interatrial communication is closed, and clot removed. Although tricuspid valve regurgitation is variable in these patients and can be severe, tricuspid valve repair is not performed unless the tricuspid annulus is > 4 cm and there is severe regurgitation. If other cardiac procedures are required, these are performed conveniently during the systemic rewarming period. Figure 5 shows a typical specimen removed form a patient with bilateral main pulmonary artery disease, along with the preoperative findings on the patient’s pulmonary angiogram.
Citation: Advances in Pulmonary Hypertension 21, 3; 10.21693/1933-088X-21.3.73
Patients are weaned from cardiopulmonary bypass in the usual manner, with the use of dopamine and other vasoactive agents. Wound closure is routine. The cardiac output tends to be high with low systemic vascular resistance, and despite the long time on cardiopulmonary bypass, blood products are generally unnecessary. Patients tend to have vigorous auto-diuresis immediately postop.
POSTOPERATIVE MANAGEMENT
The postoperative management of PTE patients is similar to that of other postoperative heart and lung surgery patients, centered on hemodynamic support and optimizing oxygenation and fluid management. Patients are hemodynamically supported on dopamine and atrially paced, with a goal cardiac index of 2 to 3 L/min/m2, as a cardiac index > 3 L/min/m2 can be associated with the development of reperfusion pulmonary edema. Patients remain intubated overnight to allow for careful monitoring of oxygenation, fluid balance, and bleeding. They are kept on the dry side with intravenous furosemide, though frequently they auto-diurese on their own for the first several hours. Anticoagulation with a heparin drip is started within a few hours, as long as bleeding is at a minimum. The anticoagulation therapy and target levels are dictated by the presence of an underlying hypercoagulable condition, as well as the risk for rethrombosis. The temporary pacing wires are typically removed on the first postoperative day, unless the patient requires pacing. Once the pacing wires are removed, coumadin is started, with a heparin drip used for bridging. The goal partial thromboplastin time (PTT) is typically 60 to 80 seconds, alternatively anti-Xa levels are monitored with a goal of 0.35 to 0.7 U/mL, and a goal international normalized ratio (INR) of 2.5 to 3.5. In patients with antiphospholipid antibodies or unilateral disease, who are at a higher risk of rethrombosis, the goal INR is 3 to 4.
COMPLICATIONS
In addition to the complications seen in other forms of open heart and major lung surgery, patients who undergo PTE may develop complications specific to this operation, such as airway bleeding, reperfusion pulmonary edema, and residual PH.
Airway Hemorrhage
Frank blood from the endotracheal tube signifies a mechanical violation of the blood-airway barrier that has occurred at the time of operation. This complication can stem from a technical error, or inadvertent opening of a communicating channel with an enlarged bronchial collateral during endarterectomy. Airway bleeding should be managed, if possible, by identification of the affected area by bronchoscopy and balloon occlusion of the affected lobe until coagulation can be normalized. Utilization of extracorporeal membrane oxygenation (ECMO) can be very helpful in managing significant airway hemorrhage, and choices of both veno-arterial (VA) and veno-venous (VV) ECMO can be considered, although in patients with severe airway hemorrhage related to vascular injury, VA ECMO may be more appropriate. In some patients, hemoptysis from a bronchial collateral can be encountered, as airway bleeding starts with bright red blood while the patient is still on full cardiopulmonary bypass, with no pulmonary artery flow. This may subside and fully resolve with termination of bypass and full forward flow through the pulmonary circulation. It is rare to require bronchial artery embolization following successful endarterectomy, but this can be a consideration, particularly in patients with severely dilated bronchial collaterals. In contrast, the amount of airway bleeding secondary to vessel wall injury directly correlates with the amount of pulmonary artery flow, and will be at its worst upon termination of bypass. There have been reports of successful management of severe airway hemorrhage by temporary institution of VA ECMO in the operating room and complete reversal of anticoagulation, with subsequent separation from ECMO over the next few hours.20–21
Regardless, the principles of management involve adequate protection of the unaffected lung, adequate ventilation and oxygenation to allow safe separation from cardiopulmonary bypass, and reversal of anticoagulation. Many patients can tolerate single-lung ventilation with endobronchial blockage of the affected lung, with subsequent deflation and removal of the endobronchial blocker once there is no evidence of further hemoptysis despite systemic anticoagulation. In those who cannot tolerate single-lung ventilation, ECMO should be instituted.
Reperfusion Pulmonary Edema
Reperfusion pulmonary edema is a syndrome that develops because of restoration of blood flow to an area of the lung that has been endarterectomized. Reperfusion pulmonary edema is defined as a Pao2/Fio2 ratio < 300, and an opacity on the chest x-ray in a region of a reperfused lung, with no alternative explanation for the opacity. True reperfusion injury that has a direct adverse impact on the clinical course of the patient occurs in approximately 10% to 15% of patients. In its most dramatic form, it occurs soon after operation (within a few hours) and is associated with profound desaturation. Edema-like fluid, sometimes with a bloody tinge, is suctioned from the endotracheal tube. Management of reperfusion pulmonary edema centers around supportive care with oxygen and positive end-expiratory pressure and the use of diuretics. Steroid administration is discouraged, as it has not been shown to be effective and may increase the risk of infection.21 Infrequently, inhaled nitric oxide at 20 to 40 parts/million can improve gas exchange. In severe cases, the authors have used VV and VA ECMO. VV ECMO is used in most patients, VA ECMO is reserved for patients who have persistent PH and/or right heart failure. ECMO support is continued until ventilation can be resumed satisfactorily, which could take several days, and rarely as long as 2 to 3 weeks. In general, VV ECMO is preferred to VA ECMO, whenever possible. If VA ECMO is used, it is important to ensure that there is adequate forward flow through the newly endarterectomized pulmonary arteries. Otherwise, resultant pulmonary thrombosis can occur, which can be catastrophic. Historically, patients who require VA ECMO have a worse prognosis than patients requiring VV ECMO.
Residual Pulmonary Hypertension
In cases of persistent severe PH, right heart dysfunction or failure following PTE, and/or hemodynamic impairment refractory to inotropic and pressor support, VA ECMO can be used. This can provide a window for possible remodeling and improvement of function, or provide a bridge while other forms of treatment are used. In extreme cases, this can also provide a bridge to possible lung transplantation.
For patients whose residual PH and accompanying right heart dysfunction is persistent despite being able to wean off ECMO, there are now approved forms of medical therapy which can be used. Riociguat is a soluble guanylate cyclase simulator that has been shown to be beneficial in patients who have residual PH following PTE. This is particularly effective for patients in whom microvascular disease exists.4 Of course, if there are concerns for residual thromboembolic disease that was beyond surgical accessibility (distal subsegmental branches), BPA should be considered. If a significant amount of residual obstructive disease is encountered in the pulmonary vasculature as a direct result of incomplete endarterectomy or possible recurrent disease, a second surgical opinion and evaluation at an expert center should be obtained. In such cases, the patient may benefit from repeat operation. In recent years, we are seeing more referrals to our center due to incomplete endarterectomy. Regardless of etiology, appropriate treatment modality and management of this postoperative complication can be challenging. In many patients this can be a multimodality approach, including medical therapy, BPA, ECMO, possible reoperation, and consideration of transplantation. Based on such experiences, guidelines from the World Symposium on Pulmonary Hypertension recommend that centers performing PTE have the capability of advanced therapy, including ECMO.
OUTCOME
The ages of the patients in our series have ranged from 6 to 89 years. A typical patient will have a severely elevated PVR level at rest, the absence of significant comorbid disease unrelated to right heart failure, and the appearances of chronic thrombi on angiography that appear to be in balance with the measured degree of PVR. Exceptions to this general rule, of course, occur.
Although most patients have a PVR level in the range of 600 to 700 dyn · s · cm−5 and pulmonary artery pressures less than systemic, the hypertrophy of the right ventricle that occurs over time makes suprasystemic PH possible. Therefore, many patients possess PVRs > 1000 dyn · s · cm−5 and suprasystemic pulmonary artery pressures. There is no upper limit of PVR, pulmonary artery pressure, or degree of right ventricular dysfunction that excludes patients from the operation, as long as there is a corresponding amount of disease present.
Our last large series from UCSD demonstrated a mortality of 4.1% for patients with preoperative PVR >1000 dyn · s · cm−5 compared with 1.6% for PVR < 1000 dyn · s · cm−5.22 Persistent PH following PTE has a much more dramatic influence on operative and 1-year mortality than elevated preoperative PVR. In 500 consecutive cases performed at UCSD, mortality was 10.3% for patients with a postoperative PVR > dyn · s · cm−5 compared with 0.9% for patients with a postoperative PVR < 500 dyn · s · cm−5.22 All efforts should be made to perform complete endarterectomy to avoid persistent PH. Distal location of thrombotic material and thus surgical accessibility plays a significant role in determining operability. Based on data from the European CTEPH registry, coronary artery disease increases in the hospital and 1-year mortality associated with the surgery from 2.1% to 10% and 5.1% to 15% respectively.5 Other factors that make the surgery technically more difficult but have not been shown to increase mortality include elevated body mass index, taller patient height, and the presence of prior sternotomy.11
Cannon et al23 looked at long-term survival and outcomes following pulmonary endarterectomy. Long-term survival of patients post PTE surgery at 5 and 10 years were 79% and 72% respectively. However, when in-depth analysis of survival was performed following the initial experience with 500 cases, survival at 5 years for the remaining 442 patients was 90%, clearly highlighting the importance of surgeon and center experience. Furthermore, 85% of patients had a significant improvement to functional class I or II, from a baseline of 91% in class III or IV. Although 51% of patients had residual PH (mean pulmonary artery pressure > 25 mm Hg), long-term follow-up suggested that the majority of patients maintained good functional status. Only a mean pulmonary artery pressure > 38 mm Hg or PVR > 425 dyn · s · cm−5 was associated with worse long-term survival.23
As mentioned above, surgeons have become increasingly aware of the changes that can occur in the remaining patent (unaffected by clot) pulmonary vascular bed subjected to the higher pressures and flow that result from obstruction in other areas. Therefore, with the increasing experience and safety of the operation, the authors tend to offer surgery to symptomatic patients whenever the angiogram demonstrates thromboembolic disease. CTED refers to a subgroup of patients who have evidence of chronic thromboembolic obstruction and have normal pulmonary artery pressures and right ventricular function at rest, but can have elevated pulmonary pressures with exercise. This is typically a young patient with uni-lateral pulmonary artery occlusion and unacceptable exertional dyspnea because of an elevation in dead space ventilation. Surgery, in this circumstance, is performed to reperfuse lung tissue, reestablish more normal ventilation-perfusion relationships (thereby reducing minute ventilatory requirements during rest and exercise), and preserve the integrity of the contralateral pulmonic circulation.
RECENT ADVANCES
Over the last decade, several innovations have enhanced surgical techniques and approach. Perhaps the most important surgical advancement has been redefining the limits of distal endarterectomy. In expert centers, PTE surgery can be successfully performed in patients with distal disease. This is attributed to advances in technology, instruments, and surgical experience. With the advent of newly designed surgical instruments and retractor, we are now able to visualize distal pulmonary vasculature better and are able to remove disease that may be limited to only segmental and/or subsegmental vessels. By utilizing the techniques described above, we are now able to offer surgery to patients with distal disease, whom we may have turned down in the past.
Over the last several years a new surgical classification (UCSD Level Classification) has been developed to reflect the level versus type of disease (ie, lobar, segmental, subsegmental); see Table 1.1,9–11,24
This classification allows accurate intraoperative designation of the location of disease, while indicating the degree of difficulty of the operation; thus, the higher the level of disease, the more challenging the operation. Depending on the experience of a center, operability determination may vary. A new definition of an expert center has been proposed, and includes the following: surgical mortality < 5%, surgical volume > 50 cases/y, and the ability to perform segmental endarterectomy at a center that offers all treatment modalities (PTE, BPA, medical therapy).9
Also, more recently, the team at UCSD sought to determine if a minimally invasive approach to PTE surgery was possible.2,3 Initial laboratory experiments were performed on multiple cadavers, which proved feasibility of performing a full endarterectomy into distal, segmental, and subsegmental arteries via miniature anterior thoracotomy incisions, while providing adequate exposure. Using a preoperative computed tomography scan for surgical planning, the procedure is performed utilizing the second, or the third intercostal space through bilateral or unilateral miniature anterior thoracotomies approximately 4 to 5 cm in length. The ideal location of the incisions is both high enough for central aortic cannulation, yet low enough for access to the pulmonary arteries. The arterial cannula is placed centrally in the ascending aorta, and venous cannulae in the femoral vein, right atrium, and/or right internal jugular vein. For all patients, cross-clamp and cardioplegia were not used for purposes of simplification and to maximize space. An aortic root vent is intermittently utilized just prior to going back on cardiopulmonary bypass with each circulatory arrest. Pulmonary artery and left atrial vents are used. The usual protocol for circulatory arrest and exposure of the pulmonary arteries was used. The minimally invasive approach to PTE surgery is not recommended for the novice PTE or minimally invasive cardiac surgeon.
In addition to the advances in surgical techniques, as well as less invasive procedures, there have also been significant improvements in management of postoperative complications. As we have gained quite a bit of experience using ECMO for a variety of cardiopulmonary diseases, we are able to utilize ECMO more successfully for certain postoperative complications in the PTE patient population. ECMO is quite helpful in management of severe reperfusion pulmonary edema, as well as significant airway hemorrhage, thereby improving overall prognosis and outcome in these devastating complications. Furthermore, in select patients with severe right heart dysfunction and persistent PH, ECMO can also be used as a bridge to recovery or further therapy. Expertise in initiation and management of VV, as well as VA, ECMO has afforded us a very important tool in the armamentarium of management of post-PTE complications. Although its use remains at a low number, over the last decade we have witnessed a steady improvement in outcomes of patients who would have been otherwise severely ill because of these complications, with questionable survival.
CONCLUSION
It is increasingly apparent that PH caused by chronic pulmonary embolism is a condition that is underrecognized and carries a poor prognosis. Medical therapy is ineffective in prolonging life and only available for patients who are not surgical candidates or have residual PH following surgery. PTE is the guideline-recommended treatment of choice for CTEPH as it has excellent long-term outcomes, and advances in surgical techniques are leading to refinement of operability definitions and improved outcomes. As a result, many previously inoperable patients with more distal disease or higher surgical risk can now be considered operable at expert centers. Although PTE is technically demanding for the surgeon and requires careful dissection of the pulmonary artery planes and the use of circulatory arrest, excellent short- and long-term results can be achieved, as long it is performed at expert centers. The mortality for thromboendarterectomy at our institution is currently in the range of 1% to 1.8% with sustained clinical benefit. In the future, multimodal therapy with PTE, BPA, and/or medical therapy is likely to be an important treatment strategy for many patients. These treatment options should be looked as complimentary to each other, as opposed to being in competition.
Treatment options for chronic thromboembolic pulmonary hypertension. A schematic representation of a pulmonary artery is shown (note that vessel diameter is not to scale). Pulmonary thromboendarterectomy (PTE) is used to remove thromboembolic lesions primarily in the proximal main artery (diameter of 1–3 cm), and lobar and segmental arteries; in expert surgical centers, lesions in distally located midsegmental and subsegmental branches can be targeted by PTE, down to vessels of 2 to 3 mm in diameter. Balloon pulmonary angioplasty mainly targets distal lesions in the segmental and subsegmental vasculature, down to small pulmonary arteries of 1 to 5 mm in diameter. Medical therapy targets microvasculopathy, including intimal thickening and fibromuscular proliferation, in vessels of 0.1 to 0.5 mm in diameter. Typical surgical specimens based on the most proximal level of obstruction are shown. The scale is in centimeters.
Surgical field view. Please note the high ascending proximal arch aortic cannulation. Typically, the SVC and IVC cannulae are crossed for easier initiation of bypass, without manipulating the right heart. SVC indicates superior vena cava; IVC, inferior vena cava; PA, pulmonary artery; and LA, left atrium.
Right pulmonary artery exposure and dissection. Please note the approach is between the aorta and the SVC. SVC indicates superior vena cava; and PA, pulmonary artery.
Typical chronic thromboembolic pulmonary hypertension findings within the pulmonary artery. Please note this picture is taken with the camera coming on the right side of the patient with the aorta retracted to the left side, and at the top of the picture.
Specimen removed from a patient with bilateral main pulmonary artery disease (right and left level I disease). Please note the corresponding intraoperative findings with preoperative pulmonary angiographic findings.
Contributor Notes