Abstract 10899: Excessive Right Ventricular Afterload in Pulmonary Arterial Hypertension: Effects on Diastolic Function and the Left Ventricle

Abstract

Introduction: Right ventricular (RV) diastolic dysfunction in pulmonary arterial hypertension (PAH) remains poorly understood. In this study, we used RV pressure-volume (PV) loops to assess RV diastology as a function of afterload in PAH. Methods: RV PV loops were prospectively measured in control (n=9) and PAH (n=39) patients at rest and during supine bike exercise. PAH patients were stratified by effective arterial elastance (Ea), a lumped measure of total afterload, into two groups: high afterload (HA, n=20) and severe afterload (SA, n=19). Results: PAH groups were matched with respect to age, sex, and PAH medication usage. Ea at rest and exercise was higher in SA PAH (1.8 vs. 0.6 mmHg/ml, P <0.0001 at rest; 2.3 vs 0.8 mmHg/ml, P < 0.0001 with exercise). In the SA group, RV end-diastolic pressure (RVEDP) was higher at rest (13.3 vs 7.6 mmHg, P = 0.0017) and rose markedly with exertion (23.4 vs 13.1 mmHg, P=0.0001). Because RV volumes changed similarly in both groups, SA patients exhibited stiffer RVs (dP/dV 0.30 vs 0.11 mmHg/mL, P=.024). To understand pericardial-interventricular interactions, we calculated the RVEDP-to-pulmonary capillary wedge pressure (PCWP) ratio and the left ventricular (LV) transmural filling pressure (LVTMFP). RVEDP/PCWP was substantially higher in SA (2.1 vs 1.0, P=.005). Therefore, even though PCWP rose considerably in SA (mean 16 mmHg), exercise LVTMFP was significantly reduced in SA vs HA PAH (-7.5 vs 2.55 mmHg, P=0.002). Along with reduced LV size seen by concomitant echo, we thus revealed blunted LV filling specifically in SA PAH. Accordingly, exercise cardiac index, stroke volume index, and LV stroke work index were all markedly reduced in SA PAH. Conclusions: Severe afterload in PAH results in high RV diastolic pressures and RV stiffening, which in turn blunt LV filling and LV output with exertion. Due to ventricular interactions, exercise PCWP may rise considerably in PAH, thus reducing its ability to differentiate from left heart disease.