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Diseases of the Pulmonary Arteries
In this chapter, five diseases involving the pulmonary arteries that are amenable to surgical treatment are discussed: acute massive pulmonary embolism, chronic pulmonary thromboembolic disease, pulmonary artery aneurysm, pulmonary artery dissection, and pulmonary artery tumors.
Section I
Acute Massive Pulmonary Embolism
Definition
Acute massive pulmonary embolism is sudden entrapment in pulmonary arteries of dislodged thrombus, usually from deep veins of the legs, pelvis, or arms. It is life threatening and can result in right heart failure, low cardiac output, and sudden death.
Historical Note
The first pulmonary embolectomy was performed by Trendelenburg in 1908, but long-term survival using his technique was not achieved until 1924. It is prophetic and of great significance that Dr. John Gibbon, who in 1953 performed the first successful operation in which a patient was totally supported by cardiopulmonary bypass (CPB) using a pump-oxygenator, envisaged use of CPB to treat massive pulmonary embolism. In 1931, while working as a research fellow for Dr. Edward Churchill, he wrote the following words in a patient's chart at Massachusetts General Hospital:
During that long night's vigil, watching the patient struggling for life, the thought naturally occurred to me that the patient's life might be saved if some of the blue blood in her veins could be continuously withdrawn into an extracorporeal blood circuit, exposed to an atmosphere of oxygen, and then returned to the patient by way of a systemic artery in a central direction. Thus, some of the patient's cardiorespiratory functions might be temporarily performed by the extracorporeal blood circuit while the massive embolism was surgically removed.
The first successful pulmonary embolectomies performed with use of CPB were reported by Cooley and colleagues in l961 and by Sharp in 1962. This remains the preferred technique for surgical treatment of acute massive pulmonary embolism.
Morphology
Detached venous thrombi pass through the right heart and enter the pulmonary arteries as a single thrombus or as fragmented smaller thrombi. The majority lodge in the lower lobes, slightly more often in the right than left lung. Shortly after reaching the lungs, emboli become coated with a layer of platelets and thrombin. Pulmonary arterial obstruction and release by platelets of vasoactive agents such as serotonin, adenosine diphosphate, platelet-derived growth factor, and thromboxane elevate pulmonary vascular resistance (Rp). Alveolar dead space increases as a result of redistribution of blood flow, and gas exchange is impaired. As right ventricular (RV) afterload increases, RV pressure rises. This may result in RV dilatation, ischemia, and dysfunction. Increased Rp results in reduced RV stroke volume and left ventricular filling (preload). Reduction in preload and coronary blood flow associated with systemic hypotension markedly reduces left ventricular stroke volume. If a patent foramen ovale or atrial septal defect is present, right-to-left shunting of blood and severe hypoxemia may occur, as may paradoxical embolization.
Clinical Features And Diagnostic Criteria
Symptoms
Acute massive pulmonary artery embolism can result in dyspnea, tachypnea, tachycardia, diaphoresis, cyanosis, and occasionally loss of consciousness.
Signs
The patient may be hypotensive, dyspneic, and cyanotic, and there may be evidence of pulsus paradoxus. Evidence of low cardiac output is present, with weak peripheral pulses and oliguria. Jugular venous pressure is elevated, often with a prominent a wave, and neck veins may be distended. Cardiac examination may demonstrate tachycardia, a prominent RV impulse, a loud pulmonary component of the second heart sound, and a gallop rhythm. An ejection or pansystolic murmur is often present that may represent tricuspid valve regurgitation. Rarely is there evidence of airway obstruction.
Diagnostic Studies
In patients in cardiogenic shock, performing studies to establish the diagnosis of pulmonary embolism is often not possible, and diagnosis is made based on presenting symptoms and signs, recognizing that the diagnosis may be incorrect. The electrocardiogram (ECG) may demonstrate T-wave inversion in the anterior leads, reflecting inferoposterior ischemia from pressure overload, a pseudoinfarction pattern, or an S1Q3T3 pattern. Transthoracic echocardiography (TTE) is particularly useful in patients suspected of having pulmonary emboli, because it can identify RV pressure overload ( Fig. 27-1 ). Transesophageal echocardiography (TEE) can demonstrate pulmonary artery thrombi as well as RV overload. Computed tomography (CT) of the chest with contrast medium can also detect thromboemboli in the major pulmonary arteries ( Fig. 27-2 ). Gadolinium-enhanced magnetic resonance imaging (MRI) can identify pulmonary thromboemboli and RV wall motion abnormalities. Contrast pulmonary angiography is a definitive diagnostic study but is infrequently performed in hemodynamically unstable patients.
![Figure 27-1, Transthoracic echocardiogram of acute massive pulmonary embolism (parasternal short axis views of right and left ventricles in diastole [A] and systole [B] ). There is diastolic and systolic bowing of interventricular septum (arrows) into left ventricle (LV)—a finding compatible with presence of right ventricular volume and pressure overload, respectively. Right ventricle (RV) is appreciably dilated and hypokinetic, with little change in apparent right ventricular area from diastole to systole. There is a small pericardial effusion (PE).](https://storage.googleapis.com/dl.dentistrykey.com/clinical/DiseasesofthePulmonaryArteries/0_3s20B9781416063919000279.jpg "Figure 27-1, Transthoracic echocardiogram of acute massive pulmonary embolism (parasternal short axis views of right and left ventricles in diastole [A] and systole [B] ). There is diastolic and systolic bowing of interventricular septum (arrows) into left ventricle (LV)—a finding compatible with presence of right ventricular volume and pressure overload, respectively. Right ventricle (RV) is appreciably dilated and hypokinetic, with little change in apparent right ventricular area from diastole to systole. There is a small pericardial effusion (PE).")
Natural History
In the United States, approximately 100,000 patients are diagnosed with acute pulmonary embolism each year, resulting in thousands of recognized deaths. Many additional deaths occur each year as a result of undiagnosed massive pulmonary embolus that is mistaken for acute myocardial infarction or ventricular arrhythmia. In the International Cooperative Pulmonary Embolism Registry of 2454 consecutive patients with acute pulmonary embolism from 7 countries, 4.2% had massive embolization.
Untreated massive pulmonary artery embolism, when accompanied by hypoxemia and hemodynamic instability, is nearly always fatal. Most deaths occur before effective treatment can be initiated. It is estimated that mortality for an obstruction of more than 50% of the pulmonary vasculature approaches 50%, and that it increases to 70% if the patient requires vasopressor therapy. If clinical deterioration continues, mortality approaches 100%.
Technique Of Operation
Preoperative Preparation
As soon as massive pulmonary embolism is suspected, high-dose unfractionated heparin should be administered. Most patients should receive a 10,000-unit bolus followed by a continuous infusion of at least 1250 units/h, with a targeted activated partial thromboplastin time (APTT) of at least 80 seconds.
Maintaining adequate oxygenation and cardiac output before establishing CPB is essential. Endotracheal intubation should be established if hypoxemia is present. If adequate cardiac output cannot be maintained with vasopressors, phosphodiesterase inhibitors, and sodium bicarbonate, or if external cardiac massage is required, CPB should be established by peripheral cannulation (see “Cardiopulmonary Bypass Established by Peripheral Cannulation” in Section III of Chapter 2 ). Heparin (300 units · kg −1 ), if not already given, should be administered as soon as it is determined that operative intervention is indicated. If the patient's condition permits, the usual preparations for establishing CPB are made (see “Preparation for Cardiopulmonary Bypass” in Section III of Chapter 2 ). If diagnosis of pulmonary embolism has not been made with certainty before the patient is transported to the operating room, TEE should be performed to establish the diagnosis before the chest is opened.
Pulmonary Embolectomy
A midline sternotomy is performed. If peripheral cannulation has not been established, cannulae are placed in the aorta and both venae cavae. If the femoral vein has been cannulated, a second venous cannula is positioned in the superior vena cava, and the femoral vein cannula is withdrawn from the right atrium into the inferior vena cava. Alternatively, a long, two-stage cannula can be used. CPB is established with mild hypothermia, and tapes are placed around the superior and inferior venae cavae and secured. The aorta is clamped and cardioplegic solution infused into the aortic root (see “Methods of Myocardial Management during Cardiac Surgery” in Chapter 3 ). Alternatively, the heart can be kept beating or fibrillating. The left atrium and left ventricle can be decompressed with a venting catheter inserted into the right superior pulmonary vein.
The pulmonary trunk is incised longitudinally several centimeters from the pulmonary valve. Using forceps and suction, the thrombus is removed. If necessary, the incision can be extended into the left pulmonary artery, and a separate incision can be made in the right pulmonary artery between the superior vena cava and ascending aorta. A sterile fiberoptic bronchoscope can be used to visualize and remove thrombus from secondary and tertiary branches of the pulmonary arteries. The pleural spaces can be incised, and the lungs gently massaged to dislodge smaller thrombi. Alternatively, retrograde perfusion of the pulmonary veins through the opened left atrium can remove additional thromboembolic material from smaller pulmonary arterial branches (along with entrapped air). The right atrial and RV cavities are explored through a right atriotomy to search for and remove residual thrombi.
After removing the thrombus, incisions in the pulmonary arteries and right atrium are closed with continuous 5-0 polypropylene suture. After completion of rewarming and evacuation of air from the cardiac chambers, CPB is discontinued. The procedure is completed in the standard manner (see “Completing Cardiopulmonary Bypass” in Section III of Chapter 2 ).
Placing an inferior vena caval clip or filter is advisable in the majority of patients. A clip can be placed after completing the embolectomy by extending the median sternotomy to the level of the umbilicus and exposing the inferior vena cava using the Kocher maneuver. Alternatively, under fluoroscopic guidance, a vena caval filter can be positioned through the femoral vein at the end of the operative procedure.
Special Features Of Postoperative Care
Postoperative circulatory support with an RV assist device and intraaortic balloon counterpulsation or extracorporeal life support can be beneficial for patients with persisting severe RV failure after embolectomy.
Anticoagulation with warfarin is recommended for a minimum of 6 months if there is no contraindication. If not already in place, an inferior vena caval filter should be inserted into patients for whom anticoagulant therapy cannot be used.
Results
Hospital mortality is variable and depends largely on the patient's hemodynamic state at the time of embolectomy. Among patients who require cardiopulmonary resuscitation or institution of CPB before operation, mortality has ranged from 45% to 75%. Mortality is substantially less (3% to 36%) for patients who are more hemodynamically stable. Although satisfactory results were obtained by Clarke and Abrams without CPB, review of a multicenter study by Del Campo demonstrated 40% early mortality for 651 patients operated on with CPB, and 51% for patients in whom CPB was not used. A more recent review by Stein and colleagues of patients operated on after 1985 reported an early mortality of 20%. Two individual series of patients operated on since 1999 have reported 30-day mortality of 6% (3 of 47 patients) and 8% (4 of 25 patients). Instituting CPB in patients who are in shock permits salvage of some who cannot be saved by alternative techniques. Principal modes of death following embolectomy are cardiac failure, brain injury, and sepsis.
Recurrent embolism is uncommon among hospital survivors. The majority maintain normal exercise tolerance and pulmonary artery pressures.
Indications For Operation
Surgical pulmonary embolectomy is indicated in patients who do not respond to aggressive resuscitative measures or require instituting CPB for cardiogenic shock, and in whom thrombolysis or percutaneous catheter-based interventions are contraindicated or unsuccessful. It should also be considered in selected patients who are at substantial risk for thrombolysis, or when there is insufficient time for thrombolysis to be effective.
Special Situations And Controversies
Thrombolytic Therapy
Thrombolysis, which dissolves fibrin, can be life saving in patients with massive pulmonary embolism, overt hemodynamic instability, and cardiogenic shock. However, the potential benefit of this form of treatment must be weighed against risk of major hemorrhage, which increases with increasing age and body mass index. In a report by Gulba and colleagues comparing medical and surgical treatment of massive pulmonary embolism and shock, 10 of 13 patients (77%; CL 59%-90%) treated surgically survived. Twenty-four patients were given alteplase (tissue plasminogen activator [tPA]) until systemic and pulmonary artery pressures stabilized; heparin was given thereafter. Sixteen of these patients (67%; CL 54%-78%) survived ( P = .5). However, major nonfatal hemorrhage occurred in 28% of the alteplase-treated patients, and 20% had recurrent embolization.
Current thrombolytic therapy most commonly involves use of recombinant human tissue plasminogen activator (tPA). One hundred milligrams is given via continuous intravenous infusion over 2 hours with or without concomitant intravenous heparin. This therapy elevates the risk of major catastrophic bleeding, and despite its use for patients with massive pulmonary embolism, no survival benefit over embolectomy has been demonstrated in large clinical trials.
Transvenous Catheter Pulmonary Embolectomy
Several catheter-based techniques have been evaluated for treating pulmonary embolism. The objective is to reduce Rp resistance and RV afterload and increase cardiac output. Techniques include (1) transvenous catheter embolectomy, which uses a steerable cup catheter to which suction is applied, (2) use of a catheter that delivers high-velocity jets of saline that draw thrombus toward the catheter and subsequently pulverize the clot, and (3) mechanical fragmentation using various devices combined with pharmacologic thrombolysis. The largest experience in the absence of thrombolytics is with the aspiration technique. Among 89 patients treated with this technique, 30-day mortality was 25% ( n = 22; CL 20%-29%). Clinical success, defined as immediate hemodynamic improvement, occurred in 72 patients (81%; CL 77%-85%). Catheter intervention is currently indicated in patients with acute massive pulmonary embolism in whom an increased bleeding risk precludes administering systemic standard-dose fibrinolysis, and in patients not considered candidates for surgical embolectomy.
Section II
Chronic Pulmonary Thromboembolic Disease
Definition
Chronic pulmonary thromboembolic disease is entrapment of thrombi in pulmonary arteries from a single episode or repeated embolic episodes that subsequently organize, or thrombi that develop in situ in the pulmonary arteries into firm, fibrous tissue that becomes incorporated into the vessel wall. These processes result in variable degrees of pulmonary artery obstruction and consequent pulmonary hypertension when obstruction becomes severe. It is estimated that chronic pulmonary thromboembolic disease develops in 1% to 5% of all cases of acute pulmonary embolism.
Historical Note
Chronic pulmonary embolism was suspected by Hart in 1916 and by Molle in 1920, but it was not until 1928 that Ljungdahl described two symptomatic patients with chronic obstruction of the pulmonary arteries who ultimately died of right heart failure. The first successful embolectomies for recurrent pulmonary embolism were reported by Allison and colleagues in 1958 and by Snyder and colleagues in 1962. The technique was refined by Cabrol and colleagues, who used a lateral thoracotomy approach to obtain access to distal branches of the pulmonary arteries. Subsequently, several small series of patients were reported by Sabiston, Daily, and Dor and their colleagues, who used the lateral thoracotomy approach or CPB with a midline sternotomy. In 1980, Daily and colleagues reported use of hypothermic circulatory arrest in combination with CPB. This technique was used to eliminate severe back-bleeding and improve visualization of the pulmonary arteries during endarterectomy. It is currently the preferred method of management.
Morphology
The chronic thromboembolic process typically involves the proximal pulmonary arteries from trunk to sublobar levels. The distal arterial vasculature remains patent. This forms the basis for surgical treatment of this disorder. The disease can result from a single embolic episode with nonresolution of large thromboemboli or from repeated embolic episodes. Pulmonary arteries remaining unobstructed are chronically exposed to high flow and eventually high pressure. As a result, the proximal patent pulmonary arteries become greatly enlarged, and the distal arterial vasculature develops characteristic changes of pulmonary hypertension (i.e., intimal proliferation and medial hypertrophy as described in Chapter 35 , Box 35-3). Plexiform lesions in adult lungs that are diagnostic of primary pulmonary hypertension have been observed in chronic thromboembolic pulmonary hypertension.
The occlusive process is commonly discrete and central. When the thrombi become fibrotic and endothelialized, they no longer respond to thrombolytic or anticoagulant therapy. Occasionally, fresh thrombus is attached to the organized thrombus. Microscopically, thrombotic material demonstrates well-organized fibrous tissue, penetrating blood vessels, elastic fibers, and absence of endothelial cells. There is intimal and medial hyperplasia. Infarction of lung tissue infrequently occurs.
Clinical Features And Diagnostic Criteria
Symptoms
In general, symptoms do not develop until months or years after the embolic event. They occur as a result of pulmonary hypertension and RV failure. Dyspnea with exertion is the most frequent presenting symptom. Other symptoms include fatigue, substernal chest pain with exercise, pleuritic pain, and hemoptysis.
Signs
Pertinent physical findings are related to right heart failure: jugular venous distention, hepatomegaly, ascites, and peripheral edema. The RV may be palpable near the lower left sternal border, and the pulmonic second sound accentuated and split. If right heart failure is severe, a murmur of tricuspid regurgitation is often present.
Diagnostic Studies
The chest radiograph may demonstrate RV enlargement and prominence of central pulmonary arteries. The ECG commonly shows RV hypertrophy with strain, right axis deviation, ST depression, T-wave inversion in the anterior precordial leads, and (less frequently) right bundle branch block. Pulmonary function studies are necessary to exclude restrictive or obstructive pulmonary parenchymal disease as the cause of the pulmonary hypertension.
A lung perfusion scan showing at least one segmental or larger defect is suggestive of chronic vascular obstruction. Often, however, the scan underestimates the severity of obstructive disease. CT scanning ( Fig. 27-3 ) and MRI ( Fig. 27-4 ) of the chest are important diagnostic studies and are being used with increasing frequency. Right heart catheterization is performed to measure RV and pulmonary artery pressures and document presence of shunting at the atrial or ventricular level. Pulmonary angiography is often performed as a part of right heart catheterization. It can generally be safely accomplished in patients with chronic pulmonary hypertension. A single injection of contrast material in each pulmonary artery is usually sufficient. Characteristic findings include dilated proximal pulmonary arteries, with obstruction of one or more lobar arteries and appearance of organized thrombi as filling defects, webs, or bands or completely thrombosed vessels ( Fig. 27-5 ; also see Fig. 27-4, B ). Angioscopy may be a useful adjunct to angiography, CT, or MRI when the diagnosis cannot be clearly established with those studies.
Coronary angiography should be performed in patients older than 40 to 45 years or in younger patients with risk factors for coronary artery disease if surgical treatment is contemplated, so that obstructive coronary lesions, if present, can be bypassed at the time of pulmonary endarterectomy.
Natural History
Patients with chronic pulmonary thromboembolic disease may remain asymptomatic for months or years. Hemodynamic progression may be the result of recurrent thromboembolism or in situ pulmonary artery thrombosis. Without intervention, survival is low and proportional to degree of pulmonary hypertension at time of diagnosis. In the study of Riedel and colleagues, survival at 5 years was 30% among patients with a mean pulmonary artery pressure exceeding 40 mmHg at time of diagnosis, and only 10% among those with a mean pressure above 50 mmHg. In the study of Lewczuk and colleagues, a mean pulmonary artery pressure of 30 mmHg was the threshold for poor prognosis. Among the 13 patients evaluated by Riedel and colleagues, 9 died a mean of 2.8 years after diagnosis of right heart failure; 7 of the 13 had evidence of recurrent embolization.
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