Clinical and hemodynamic correlates of pulmonary arterial stiffness in incident, untreated patients with idiopathic pulmonary arterial hypertension

Background The role of decreased pulmonary arterial (PA) compliance (C), equivalent to increased PA stiffness (1/C), as a critical determinant of right ventricular dysfunction and prognosis has been emphasized in pulmonary arterial hypertension (PAH). Methods This study retrospectively reviewed all incident patients diagnosed with idiopathic PAH according to right heart catheterization who were enrolled in the French Pulmonary Arterial Hypertension Network registry between 2006 and 2016 and who had complete baseline data allowing calculation of stiffness (PA pulse pressure/stroke volume index). Results In the 719 patients included (median age: 66 years; 53.7% female), PA stiffness was 1.49 mm Hg × m 2 /mL (interquartile ratio: 1.08-2.04 mm Hg × m 2 /mL). Stiffness was related to mean pulmonary artery pressure (mPAP) ( r 2  = 0.33) and heart rate ( r 2  = 0.15) but not to age or sex. Higher PA stiffness and higher pulmonary vascular resistance (PVR) were documented in high-risk vs low-risk patients, as defined according to the European Society of Cardiology/European Respiratory Society guidelines. The dispersion of the PVR × C product was as variable as patient age and mPAP, and C could not be estimated on the basis of PVR alone (95% limits of agreement of the bias: –50% to 54%). Although transplant-free survival differed across PA stiffness quartiles ( P  = .04), stiffness was not an independent predictor of long-term outcome (median follow-up duration: 2.43 years). Conclusions In incident idiopathic PAH, PA stiffness was related to mPAP and heart rate, and this finding outperformed the potential influences of age and sex. Baseline PA stiffness did not independently predict outcome. The great dispersion of the PVR × C product implied that PVR and PA stiffness were differently affected by the disease process.