Chronic Thromboembolic Pulmonary Hypertension




Abstract


Chronic thromboembolic pulmonary hypertension is an uncommon but increasingly recognized surgically treatable cause of pulmonary hypertension. Diagnosis is often delayed when patients present with unexplained exertional dyspnea in the absence of obvious cardiopulmonary disease. The standard evaluation process includes an echocardiogram, a ventilation perfusion scan, chest computed tomography angiography, and a right heart catheterization with a pulmonary angiogram. Most patients have surgically accessible disease when evaluated by an experienced hypertension team. The operation is standardized and performed through a median sternotomy, with standard bicaval and aortic cannulation. Hypothermic circulatory arrest is used to ensure a bloodless field. The key to the operation is selecting the proper dissection plane between the intima and the media, which allows the surgeon to dissect the specimen far out into the segmental and subsegmental pulmonary artery vessels. Anticoagulation is started early postoperatively as soon as mediastinal chest tube output is minimal. Most patients have a good result and operative mortality is now under 5% in most centers.




Keywords

chronic thromboembolic pulmonary hypertension, pulmonary thromboendarterectomy

 





Preoperative Considerations





  • Chronic thromboembolic pulmonary hypertension (CTEPH) is an increasingly recognized clinical entity. Pulmonary embolism (PE) is a common disease, with an annual incidence of about 100/100,000 in the United States. Many episodes of PE, however, are silent; from 30% to 50% of patients with CTEPH have no history of a PE. Patients with a prior PE who do not have complete fibrinolysis of their clot may go on to have the residual clot remodel into a scar, which can occlude or narrow segmental, lobar, and even main pulmonary arteries with a fibrous plug, leading to pulmonary hypertension. The incidence of CTEPH after a documented PE has been reported in several studies, and a reasonable estimate is in the 4% to 5% range. The classic study by Pengo and colleagues has suggested a 3.8% incidence of CTEPH after a PE. A more recent study has suggested a 4.8% incidence of CTEPH after a PE. Risk factors for CTEPH are listed in Table 34.1 . Although many hypercoagulable states have been documented in CTEPH patients (e.g., antithrombin III deficiency, protein C, protein S, factor V Leiden, prothrombin gene mutation), they are not more prevalent than in patients with primary pulmonary hypertension. However, antiphospholipid antibody syndrome is more prevalent in CTEPH patients.



    Table 34.1

    Risk factors for chronic thromboembolic pulmonary hypertension































    RISK FACTOR ODDS RATIO
    Previous PE 19
    Younger age 1.8/decade
    Larger defect on perfusion scan 2.2/decile decrease in perfusion
    Unprovoked PE 5.7
    Splenectomy 18
    VA shunt or infected pacemaker 76
    Chronic inflammation Increased
    Antiphospholipid antibody syndrome Increased

    PE, Pulmonary embolism; VA, ventriculoatrial.



  • The diagnostic evaluation process is relatively straightforward; the most important factor is to consider this process when a patient presents with unexplained dyspnea with a clear chest radiograph and no obvious cardiopulmonary disease. Common presenting symptoms include dyspnea on exertion, atypical exertional chest discomfort, exercise intolerance, exertional presyncope or syncope, and hemoptysis. Common signs include signs of right heart failure with lower extremity edema, hypoxemia, and occasionally pulmonary artery (PA) flow murmurs.



  • A ventilation-perfusion (V̇/Q̇) scan will show substantial segmental defects in CTEPH, whereas a normal V̇/Q̇ scan essentially eliminates CTEPH from further diagnostic consideration ( Fig. 34.1 ). An echocardiogram can then confirm significant pulmonary hypertension and screen for other cardiac disease. Complete pulmonary function tests are usually performed in older patients to screen for other pulmonary disease. In the United States, contrast-enhanced, pulmonary embolism (PE) protocol, chest computed tomography angiography (PE-CTA) is also performed to screen for other pulmonary disease and to demonstrate the PA anatomy. Findings on CT suggestive of CTEPH include a mosaic perfusion pattern, peripheral infarcts, a clot within the PA, narrowed pulmonary arteries, webs, and PA cutoffs. Dual-energy CTA is a promising imaging modality that may help better identify good operative candidates and can potentially offer a quantitative estimate of the degree of PA obstruction. Magnetic resonance angiography (MRA) is often used in European centers instead of CTA to evaluate CTEPH patients.




    Figure 34.1


    Preoperative V/Q scan in a patient with CTEPH and a pulmonary artery systolic pressure of 100. Notice the reduced global perfusion to the right lung and segmental defects.



  • A right heart catheterization is finally performed to measure the hemodynamics of the pulmonary circulation and obtain a two-plane pulmonary angiogram. Typical findings include delayed filling of vessels, branch occlusions, webs, pouches, and narrowed vessels ( Fig. 34.2 ). A left heart catheterization is performed in those with suspected or reasonably possible coronary disease based on age and atherosclerosis risk factors. Ideally, an experienced multidisciplinary CTEPH team reviews the evaluation and makes an operability decision. In general, the degree of identified PA obstruction should match the pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR). The vast majority of patients are operable in experienced centers if there are at least several segmental PA obstructions because imaging studies usually underestimate the degree of disease found at pulmonary thromboendarterectomy (PTE). True distal disease should be avoided but is uncommon. Particularly in patients with acute or chronic PE, it is important to determine if there is still clotting in the deep venous systems of the legs. If vascular ultrasound suggests this, addition of an inferior vena cava (IVC) filter should be considered. Although IVC filters are accompanied by some degree of controversy, if used in this setting, consideration should be given to removing them within 6 postoperative months. Although routine IVC filters used to be advocated for all patients with CTEPH, this is an area of unresolved controversy, and we usually do not place them in the typical patient. We have occasionally proceeded to surgery based solely on the V̇/Q̇ scan and echocardiographic estimation of PA pressure in patients with classic histories who present acutely and are very ill.




    Figure 34.2


    Pulmonary angiogram of a patient with CTEPH demonstrating missing segmental branches and pouches.






Indications for Surgery





  • The indications to perform a PTE are straightforward—a symptomatic patient, significant pulmonary hypertension, segmental or proximal obstructive disease amenable to clearance with PTE, and the absence of severe comorbid disease. A controversial indication is symptomatic patients with only exercise-induced pulmonary hypertension. The reasons for performing a PTE include not only improving exercise capacity, but also stabilizing the longer term prognosis by preventing progression of distal PA arteriopathy and continued loss of right ventricular (RV) function. Patients with atrial level shunts can also become desaturated, particularly with exercise.






Operative Steps





  • Although these patients can be hemodynamically tenuous, generally they can be anesthetized safely. A potential exception is the patient who may have acute or chronic PE, with severe right heart failure. To the extent possible, a PA catheter should be placed before the induction of anesthesia; rising central venous pressure (CVP) during the induction of anesthesia should trigger concern that right heart function is declining. Patients are positioned supine and prepped as per cardiac surgery routine. In the unusual situation in which a concomitant coronary bypass is planned, the preparation should include access for harvesting conduit. Concomitant cardiac procedures can be included and, in general, the operative strategy should include planning the concomitant procedure during rewarming after the period of hypothermic circulatory arrest needed for PTE.



  • The anesthesia technique should take into consideration minimizing right heart afterload. Hypercarbia should be assiduously avoided, and mean airway pressure should be kept to a minimum. The addition of pulmonary vasodilators has not been required. Maintaining generous systemic pressure is key to maintaining stable right heart function. Transesophageal echocardiography is routinely included and, specifically, the following issues are examined:




    • Is there a clot in transit through the right heart?



    • Is there any patency of the interatrial septum?



    • Is there severe tricuspid valve regurgitation with a dilated tricuspid annulus?



    • Is right heart function impaired and to what degree?




  • Routine median sternotomy is used, and the incision should not be made too short. These patients require generous exposure, particularly in the upper half of the thorax. The pericardium is then opened in the midline and fashioned into a cradle as usual. The superior vena cava (SVC) is then mobilized from under the pericardial reflection and off the right PA. The ascending aorta is mobilized free from the PA. Exposure and patient stability permitting, the right and left pulmonary arteries are mobilized from under their pericardial reflections. If any surgery is required through the right atrium, the IVC is also circumferentially mobilized.



  • In a given cardiac surgery center, the cannulation and perfusion protocol described here can be modified according to institution custom and practice. Aortic cannulation is per routine. Through purse-string sutures placed on the right atrial free wall, angled cannulae are inserted. The SVC purse string should be close to the cavoatrial junction so that the SVC cannula reaches well into the SVC ( Fig. 34.3 ). For the average-sized patient, a 28-mm, short-tipped cannula is placed in the IVC, and a 24 F, long-tipped cannula is directed into the SVC. The longer cannula is required for retraction of the SVC to avoid SVC obstruction while on cardiopulmonary bypass and while the SVC is being retracted. In patients who are over approximately 100 kg, a 31-mm cannula can be used in the IVC and a 28-mm, long-tipped cannula can be used in the SVC.


Jan 26, 2019 | Posted by in CARDIAC SURGERY | Comments Off on Chronic Thromboembolic Pulmonary Hypertension
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