Background: Patients with chronic thromboembolic pulmonary disease (CTED) have persistent pulmonary vascular obstruction and exercise intolerance without pulmonary hypertension at rest and may benefit from pulmonary endarterectomy. However, up to now, CTED has been poorly characterized. Objectives: This study aimed to analyze the exercise capacity and limiting factors in CTED. Methods: We compared right heart catheterization and cardiopulmonary exercise test results of patients with CTED [mean pulmonary artery pressure (mPAP) at rest <25 mm Hg, n = 10], chronic thromboembolic pulmonary hypertension (CTEPH, n = 31) and a control group (n = 41) presenting with dyspnea but normal pulmonary vascular imaging and excluded pulmonary hypertension. Results: Subjects with CTED show a reduced oxygen uptake [median 76/interquartile range (IQR) 22% pred.] and work rate (median 76/IQR 21 W). The work rate was significantly lower compared to control subjects (p = 0.04) but not significantly different from CTEPH patients (p = 0.66). Oxygen pulse and breathing reserve were normal. CTED subjects showed decreased end-tidal CO₂ at anaerobic threshold (28.4/4.3 mm Hg), an elevated VE/VCO₂ slope (42.5/23.5), breathing equivalents (EQO₂ 32.0/8.7, EQCO₂ 39.5/8.8), alveolar-capillary oxygen gradient (34.7/15.5 mm Hg) and capillary end-tidal carbon dioxide gradient (8.8/5.7 mm Hg) compared to control subjects (p < 0.001). The degree of limitation was similar to that in CTEPH. Conclusions: Despite an mPAP of <25 mm Hg, subjects with CTED show objective functional impairment and similar limitations to patients with CTEPH. Functional limitation is characterized by gas exchange disturbance and ineffective ventilation.

Background: Chronic thromboembolic pulmonary hypertension (CTEPH) is a serious complication of pulmonary embolism (PE). Taking into account the reported incidence of CTEPH after acute PE, the number of patients with undiagnosed CTEPH may be high. Objectives: We aimed to determine if cardiopulmonary exercise testing (CPET) could serve as complementary tool in the diagnosis of CTEPH and can detect CTEPH in patients with normal echocardiography. Methods: At diagnosis, we analyzed the data of CPET parameters in 42 patients with proven CTEPH and 51 controls, and evaluated the performance of two scores. Results: VE/VCO₂ slope, EQO₂, EQCO₂, P(A-a)O₂, end-tidal partial pressure of CO₂ at anaerobic threshold (PETCO₂) and capillary to end-tidal carbon dioxide gradient [P(c-ET)CO₂] were significantly different between patients with CTEPH and controls (p < 0.001). P(c-ET)CO₂ was the single parameter with the highest sensitivity (85.7%) and specificity (88.2%). A score combining VE/VCO₂ slope, P(A-a)O₂, P(c-ET)CO₂, PETCO₂ [4-parameter-CPET (4-P-CPET) score] reached a sensitivity of 83.3% and a specificity of 92.2% after cross-validation. In 42 patients with CTEPH, echocardiography identified PH in 29 patients (69%), but it was normal in 13 patients (31%). All patients with normal or unmeasurable right ventricular systolic pressure had a pathological CPET. Twelve of the 13 patients (92%) were detected by both CPET scores. Conclusion: CPET is a useful noninvasive diagnostic tool for the detection of CTEPH in patients with suspected PH but normal echocardiography. The 4-P-CPET score provides a high sensitivity with the highest specificity.

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Time delay between onset of symptoms and diagnosis of CTEPH and referral to a PH expert center is long and the majority of patients presented in WHO-functional class III or IV. Prognosis is poor in untreated patients and getting worse with a higher WHO-functional class. For this reason, and because CTEPH can be cured by a pulmonary endarterectomy, each patient with suspected PH should be referred to a PH expert center to exclude CTEPH.

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