Differences of right ventricular diastolic stiffness in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

Background: Right ventricular (RV) fibrosis contributes partly to the RV diastolic stiffness in pulmonary hypertension (PH), however it is still unknown whether this contribution is similar in different types of PH. Therefore, we investigated whether there is a different relation of RV fibrosis to RV diastolic stiffness in pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Methods: RV end-diastolic elastance (stiffness, Eed) was determined in 56 treatment-naive PH patients (PAH, n=37; CTEPH, n=19) via single-beat pressure-volume analyses. Cardiovascular magnetic resonance (CMR) native T1-mapping was used as measure for focal myocardial fibrosis using regions of interest at RV free wall and interventricular insertion points (IVIPs). Results: Both PH groups were similar in terms of age, hemodynamics (pulmonary vascular resistance and mean pulmonary artery pressure) and native T1-values of both regions of interest. We observed higher RV Eed in PAH compared to CTEPH patients (0.59±0.37 versus 0.39±0.31 mmHg·mL-1, P<0.05). In CTEPH, RV Eed was modestly related to native T1-values of the RV free wall (r=0.50; P=0.02), while a trend towards an association with IVIPs was observed (r=0.44; P=0.05). In PAH patients, RV Eed was not related to native T1-values of any region of interest. Conclusion: CMR derived focal fibrosis of the right ventricle correlates with RV diastolic stiffness in CTEPH but not in PAH. This may suggest that underlying causes of RV diastolic stiffness are different in PAH and CTEPH.