Advanced Right Ventricular Assessment: Pulmonary Artery Compliance and RV-PA Coupling

Accurate assessment of right ventricular (RV) function in pulmonary hypertension (PH) is critical for disease management as clinical outcomes are tightly linked. RV function is substantially different from left ventricular function as it is less preload responsive and much more afterload sensitive. Therefore, to fully understand the RV response in pulmonary hypertension (PH), it is useful to conceptualize it in connection to the pulmonary vasculature. This afterload on the RV is composed of a steady flow load (resistance) and pulsatile load (compliance), and these parameters have a constant, inverse relationship across subjects with various etiologies of PH with the exception of elevated pulmonary artery wedge pressure. The gold standard measure of RV function is end-systolic elastance (Ees) which represents myocardial contractility and is derived from the end-systolic pressure-volume relationship on a pressure vs. volume (PV) loop. Afterload can be estimated from the PV loop as arterial elastance (Ea), which is stroke volume/end-systolic volume. Therefore, RV-PA coupling is the ratio of Ees/Ea and is roughly 2 under normal conditions and decreases as the RV decompensates. This not only provides us with a way to understand the relationship between the RV and pulmonary vasculature, but is also predictive of outcomes in PH.