Right ventricular adaptation to pressure-overload: Differences between chronic thromboembolic pulmonary hypertension and idiopathic pulmonary arterial hypertension

Background: Chronic thromboembolic pulmonary hypertension (CTEPH) and idiopathic pulmonary arterial hypertension (iPAH) are both associated with right ventricular (RV) failure and mortality. However, CTEPH patients are older, more often male and usually have more co-morbidities than iPAH patients, including a history of venous thromboembolism. Therefore, RV adaptation to pressure-overload in CTEPH may be different than in iPAH. Methods: We included all treatment-naive CTEPH and iPAH patients diagnosed in the Amsterdam UMC between 2000 and 2019 if cardiac magnetic resonance imaging (CMR) and a right heart catheterization were performed at time of diagnosis. Load-dependent RV volumes and mass were assessed with CMR. Load-independent RV contractility, afterload and diastolic stiffness in relation to afterload were obtained using single beat pressure-volume loop analysis. Differences in RV characteristics between CTEPH and iPAH were analyzed using multiple linear regression with interaction testing after correcting for confounders. Results: We included 235 patients in this study and performed pressure-volume loop analysis in 136 patients. In addition to being older and more often male, CTEPH patients had a lower pulmonary vascular resistance than iPAH patients at the time of diagnosis. After correcting for these confounders, CTEPH patients had a somewhat higher RV end-diastolic volume index (87 ± 27 ml vs 82 ± 25 ml; p <.01), and a lower RV relative wall thickness (0.6 ± 0,1 g/ml vs 0.7 ± 0,2 g/ml; p <.01). The correlation coefficient of RV diastolic stiffness to afterload was higher in CTEPH compared to iPAH (p <.05; independent of age and gender). Conclusions: Despite differences in patient characteristics, disease etiology and physiology, RV functional parameters in CTEPH and iPAH are mostly similar. The right ventricle in CTEPH is marginally more dilated, stiffer and less hypertrophic than in iPAH.