DEFINITION
CTEPH refers to a variant of secondary PAH characterized by chronic thromboembolic obstruction of the pulmonary arteries. The obstruction may be at any level in the pulmonary arterial system, but only those involving the main, lobar or segmental arteries are amenable to surgical correction.
ETIOLOGY—KEY FACTS
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Incomplete anatomic recovery following an acute pulmonary embolic event occurs more commonly than was previously recognized.
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Estimates of the incidence of CTEPH following acute pulmonary embolism range from 0.5% to 3.8%.
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A history of acute venous thromboembolism is not present in approximately 30% of patients presenting with CTEPH.
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Factors that appear to predispose to the development of CTEPH include recurrent embolic events and single events in which more than 50% of the pulmonary vascular bed is occluded.
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Thrombophilic states associated with CTEPH include the presence of a lupus anticoagulant, elevated levels of antiphospholipid antibodies, and elevated levels of factor VIII.
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Deficiencies of protein C, protein S, antithrombin III, or the presence of factor V Leiden mutation do not appear to be associated with a higher risk of CTEPH.
CLINICAL FEATURES—SIGNS AND SYMPTOMS
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The symptoms and signs of CTEPH are similar to those of other forms of pulmonary hypertension, depend on the severity of the disease at presentation, and include
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Exertional dyspnea
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Fatigue
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Exertional chest pain
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Exertional presyncope or syncope
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Lower extremity edema
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Right ventricular lift
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Jugular venous distension
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Tricuspid or pulmonic regurgitation
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A unique physical finding in 30% of patients with CTEPH is the presence of flow bruits over the lung fields, a finding not encountered in patients with small vessel variants of PAH such as idiopathic PAH.
DIAGNOSIS
Unlike other variants of PAH, CTEPH is potentially amenable to surgical correction. The primary purpose of the diagnostic evaluation is to quantify the degree of pulmonary hypertension, to establish its etiology, and if major vessel thromboembolic disease is present, to determine whether it is amenable to surgical intervention.
IMAGING STUDIES
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Chest Radiograph
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Abnormal in majority
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Clues: enlarged central pulmonary arteries, asymmetric size of central pulmonary arteries, right ventricular enlargement, areas of parenchymal hypolucency, and peripheral scars consistent with prior infarction.
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Ventilation-perfusion (V/Q) scan
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Most useful imaging modality to separate large vessel variants of PAH (CTEPH) from small vessel variants such as idiopathic (primary) PAH.
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The V/Q scan in CTEPH is characterized by the presence of segmental or larger mismatched defects ( Fig. 52-1 ), whereas in small vessel variants, the scan is either normal or demonstrates subsegmental defects.
Figure 52-1
Lung ventilation-perfusion study in patient with chronic thromboembolic pulmonary hypertension. Large unmatched perfusion defects are seen in both lower lobes.
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Other pulmonary hypertensive disorders that may be associated with segmental or larger perfusion defects include pulmonary veno-occlusive disease, fibrosing mediastinitis, pulmonary artery sarcoma, and large vessel pulmonary vasculitis.
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The abnormalities appearing on the V/Q scan in patients with CTEPH can understate the actual degree of chronic thromboembolic obstruction. Even a single mismatched segmental defect should raise the suspicion of CTEPH.
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Computed tomographic (CT) scan
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Imaging may demonstrate a mosaic pattern of perfusion, enlargement of the right ventricle or main pulmonary arteries, and peripheral scars consistent with prior infarction.
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Contrast imaging may demonstrate filling defects within the main pulmonary arteries and the presence of bronchial artery collateral vessels.
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The absence of computed tomographic findings does not completely exclude the possibility of CTEPH.
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Useful in evaluating the pulmonary parenchyma in patients with coexisting obstructive or restrictive disease.
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Useful in evaluating the mediastinum when external compression of the pulmonary arteries is suspected (e.g., fibrosing mediastinitis, adenopathy, or malignancy).
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Magnetic resonance angiography (MRA)
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Emerging technique in the preoperative evaluation of CTEPH.
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Useful in patients with contrast allergy.
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Does not provide essential hemodynamic data necessary to determine operability and operative risk.
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Echocardiography
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Often the first technique to confirm the presence of resting pulmonary hypertension
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May demonstrate enlargement of the right atrium and right ventricle, and flattening of the interventricular septum
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Can provide an estimate of pulmonary artery pressure
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Using contrast enhancement, can detect the presence of atrial or ventricular level shunts
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Can provide useful information regarding the status of valvular structures and the left ventricle
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Right heart catheterization with conventional pulmonary angiography
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At most centers, remains the gold standard for diagnosis
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Provides essential hemodynamic data
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More sensitive than CT and MRA in evaluating the segmental pulmonary vessels
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The angiographic appearance of chronic thromboembolic disease is distinct from that of acute thromboembolic disease and is characterized by the presence of pouch defects; pulmonary arterial webs and bands; complete vascular obstruction at the main, lobar, or segmental level; abrupt vessel narrowing; and intimal irregularities ( Fig. 52-2 ).
Figure 52-2
A, The right pulmonary arteriogram of the patient whose V/Q scan is depicted in Figure 52-1 . The solid arrow highlights an angiographic “pouch” occlusion of the right interlobar vessel. The presence of organized thromboembolic disease is also evident by “web” narrowing of the proximal anterior upper lobe artery ( open arrow ). B , The lateral right pulmonary arteriogram in the same patient shows another “web” narrowing ( open arrow ) of the proximal posterior upper lobe vessel not appreciated on the anteroposterior films. C and D , The left pulmonary arteriogram reveals a “pouch defect” in the proximal upper lobe artery ( open arrow ). This is accompanied by an angiographic “web” in the proximal apical artery; the other vessels leading to the upper lobe appear to be occluded. There’s a rounded appearance ( solid arrow ) to the distal descending pulmonary artery, with a paucity of vasculature to the lower lobe. The lateral view ( D ) shows a patent lingular artery and superior segmental artery, right lower lobe. This view reveals that the posterior-lateral and anterior-medial vessels to the lower lobe are occluded.
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ADJUNCTIVE STUDIES
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Pulmonary function testing
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Recommended preoperatively to exclude the possibility of a significant coexisting obstructive or restrictive ventilatory defect
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Commonly demonstrates a mild restrictive defect thought secondary to areas of pulmonary infarction.
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Severe reduction (<50%) of the diffusing capacity for carbon monoxide is unusual and should raise the possibility of other disease processes such as pulmonary veno-occlusive disease, interstitial lung disease, or emphysema.
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Arterial blood gas analysis
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The resting arterial PO 2 may be within normal limits. However, the alveolar-arterial oxygen gradient is typically widened and the majority of patients have a decrease in the arterial PO 2 with exercise
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Hypoxemia is related to ventilation-perfusion mismatch, reduction in cardiac ouput, and right-to-left shunting in the presence of a patent foramen ovale.
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Pulmonary angioscopy
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May be a useful adjunct in a select group of patients.
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Allows visualization of pulmonary arterial walls to confirm presence of chronic thromboembolic disease and help determine if amenable to surgical intervention.
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May demonstrate webs, bands, intimal pitting, partial recanalization, masslike chronic embolic material. ( Fig. 52-3 )
Figure 52-3
A, Angioscopic view of a vessel bifurcation in a pulmonary artery free of chronic thrombus, revealing a smooth vascular intima. B, Appearance of organized thrombus through a pulmonary angioscope. Note: Recannalization and web formation.
From Fedullo PF, Auger WR, Channick RN, Kerr KM, Rubin LJ. Chronic thromboembolic pulmonary hypertension. Clin Chest Med 2001;22:561–581, with permission.
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Coronary angiography
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Patients with coronary risk factors who are deemed candidates for PTE should undergo coronary angiography before the procedure.
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Coronary artery bypass grafting can be performed at the time of thromboendarterectomy
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Inferior vena cava filter placement
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An inferior vena caval filter is recommended before PTE to protect the patient from embolic recurrence during the early, high-risk postoperative period, when anticoagulation may not be feasible and over the long-term in the event anticoagulant therapy needs to be interrupted.
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