Abstract 13087: Right Atrial Adaptation in Pulmonary Hypertension: Pressure-Volume and Histological Analysis

Abstract

Introduction: Pulmonary arterial hypertension (PAH) is associated with increased right atrial (RA) pressure and volume. We hypothesized that these patients have RA hypertrophy, increased stroke work, fibrosis and stiffness and that RA adaptation falls short in severe right ventricular (RV) diastolic stiffness (end-diastolic elastance; E ed ). Methods: RA pressure-volume loops were created through a novel method in controls (N=9) and patients (N=27). RA volume was measured on a magnetic resonance transverse stack of slices and pressure with catheterization. In a larger cohort of controls (N=20) and PAH patients with low (N=39) or high E ed (N=41), RA volume was measured on a 4-chamber view and stroke work estimated through multiplying active emptying by A-wave pressure. Atriovenous stiffness was measured as the slope from minimal pressure and volume and V-wave. In PAH-patients (N=4) and controls (N=5) that died or underwent heart- and lung-transplantation, we collected RA tissue to study hypertrophy and capillarization (CD31 and wheat germ agglutinin staining) and fibrosis (Masson’s trichrome staining). Results: Averaged pressure-volume loops show RA dilatation in patients and elevated pressure, especially during atrial contraction. Atriovenous stiffness was similar in PAH and controls, but higher in high E ed when compared to low E ed patients. RA stroke work and pressure rise during atrial contraction were higher in PAH. However, when corrected for E ed , these parameters were decreased in high E ed patients, indicating RA-RV uncoupling. Histological analysis showed increased RA hypertrophy, number of capillaries per cardiomyocyte and perivascular/interstitial fibrosis in PAH patients. Conclusions: In PAH patients there is RA hypertrophy and increased stroke work. In severe RV diastolic stiffness, RA adaptation falls short and RA-RV uncoupling occurs. Although there is increased fibrosis, atriovenous stiffness is not different between PAH and controls.