Increased right atrial volume measured with cardiac magnetic resonance is associated with worse clinical outcome in patients with pre‐capillary pulmonary hypertension

AIMS: Pre‐capillary pulmonary hypertension (PH(pre‐cap)) has a poor prognosis, especially when caused by pulmonary arterial hypertension (PAH) associated with systemic sclerosis (SSc‐PAH). Whether cardiac magnetic resonance (CMR)‐based quantification of atrial volumes in PH(pre‐cap) is beneficial in risk assessment is unknown. The aims were to investigate if (i) atrial volumes using CMR are associated with death or lung transplantation in PH(pre‐cap), (ii) atrial volumes differ among four unmatched major PH(pre‐cap) subgroups, and (iii) atrial volumes differ between SSc‐PAH and idiopathic/familial PAH (IPAH/FPAH) when matched for pulmonary vascular resistance (PVR). METHODS AND RESULTS: Seventy‐five PH(pre‐cap) patients (57 ± 19 years, 53 female, 43 de novo) with CMR and right heart catheterization were retrospectively included. Short‐axis stacks of cine images were analysed, and right and left atrial maximum (RAV(max) and LAV(max)) and minimum volume (RAV(min) and LAV(min)) were indexed for body surface area. Increased (mean + 2 SD) and reduced (mean – 2 SD) volumes were predefined from CMR normal values. Transplantation‐free survival was lower in patients with increased RAV(max) than in those with normal [hazard ratio (HR) = 2.1, 95% confidence interval (CI) 1.1–4.0] but did not differ between those with reduced LAV(max) and normal (HR 2.0, 95% CI 0.8–5.1). RAV(max) and RAV(min) showed no differences among unmatched or matched groups (P = ns). When matched for PVR, LAV(max), LAV(min), and pulmonary artery wedge pressure were reduced in SSc‐PAH compared with IPAH/FPAH (95% CI 0.3–21.4, 95% CI 0.8–19.6, and 95% CI 2–7, respectively). CONCLUSIONS: Patients with PH(pre‐cap) and increased right atrial volume measured with CMR had worse clinical outcome. When matched for PVR, left atrial volume was lower in SSc‐PAH than in IPAH/FPAH, consistent with left‐sided underfilling, indicating a potential differentiator between the groups.