Cardiac Geometry, As Assessed by Cardiac Magnetic Resonance, Can Differentiate Subtypes of Chronic Thromboembolic Pulmonary Vascular Disease

Background: Ventricular septal flattening reflects RV pressure overload in pulmonary arterial hypertension. Eccentricity index (EI) and pulmonary artery distensibility (PAD) correlate with pulmonary artery pressure. We assessed the utility of these using cardiac magnetic resonance (CMR) to assess for pulmonary hypertension (PH) in patients with chronic thromboembolic disease. This may allow non-invasive differentiation between patients who have chronic thromboembolic pulmonary hypertension (CTEPH) and those with pulmonary vascular obstructions without PH at rest, known as chronic thromboembolic pulmonary disease (CTEPD).

Methods: Twenty patients without resting pulmonary hypertension, including ten with chronic thromboembolic disease, and thirty patients with CTEPH were identified from a database at the Scottish Pulmonary Vascular Unit. CMR and right heart catheter had been performed within 96 h of each other. Short-axis views at the level of papillary muscles were used to assess the EI at end-systole and diastole. Pulmonary artery distensibility was calculated using velocity-encoded images attained perpendicular to the main trunk.

Results: Eccentricity index at end-systole and end-diastole were higher in CTEPH compared to controls (1.3 ± 0.5 vs. 1.0 ± 0.01; ≤ 0.01 and (1.22 ± 0.2 vs. 0.98 ± 0.01; ≤ 0.01, respectively) and compared to those with CTED. PAD was significantly lower in CTEPH compared to controls (0.13 ± 0.1 vs. 0.46 ± 0.23; ≤ 0.01) and compared to CTED. End-systolic EI and end-diastolic EI correlated with pulmonary vascular hemodynamic indices and exercise variables, including mean pulmonary arterial pressure (R0.74 and 0.75, respectively), cardiac output (-value -0.4 and -0.4, respectively) NTproBNP (-value 0.3 and 0.3, respectively) and 6-min walk distance (-value -0.7 and -0.8 respectively). Pulmonary artery distensibility also correlated with 6-min walk distance (-value 0.8).

Conclusion: Eccentricity index and pulmonary artery distensibility can detect the presence of pulmonary hypertension in chronic thromboembolic disease and differentiate between CTEPH and CTED subgroups. These measures support the use of non-invasive tests including CMR for the detection pulmonary hypertension and may reduce the requirement for right heart catheterization.