Coupling Right Ventricular–Pulmonary Arterial Research to the Pulmonary Hypertension Patient Bedside

ver the last decade, there has been increasing appreciation for the importance of right ventricular (RV) coupling to the pulmonary arterial (PA) circulation.This relationship, so-called RV-PA coupling, is an application of the left-sided ventriculo-arterial coupling first described in the 1980s. 1 Whether it refers to the left or right, coupling describes the energy transfer between ventricular contractility and arterial afterload.Ventricular contractility is well characterized by end-systolic elastance (Ees), a load-independent measure of systolic function.Arterial afterload, on the other hand, can be thought of in terms of net vascular stiffness.Sunagawa et al 1,2 created a term in 1983 called effective arterial elastance (Ea), which encapsulates net stiffness by combining mean and pulsatile loading to yield a lumped parameter that reflects the load imposed upon the ventricle.An important breakthrough came in 1992 when Kelly et al 3 found in humans that end-systolic pressure divided by stroke volume accurately represented Ea across a wide afterload range.Because Ea is conveniently measured using the same units as Ees, this allows the ratio of Ees to Ea to become a unit-less value that encapsulates ventriculo-arterial coupling.The ideal Ees/Ea ratio is estimated to be 1.0 to 2.0. 2 This ratio is seen in the healthy RV-PA unit and remains preserved even in the early phases of pulmonary hypertension (PH) because compensatory RV hypertrophy leads to an increase in RV Ees that matches increasing Ea.It is only with progressive RV decompensation that RV Ees begins to fall, Ees/Ea declines, and the RV-PA unit becomes uncoupled.4 RV-PA coupling is often talked about in academic circles and carefully measured in animal and human experimental studies of PH.Coupling can describe RV compensation not only in group I PH but also in PH secondary to a range of left-sided cardiac conditions.Its importance has risen alongside increasing recognition of the pivotal role that the RV plays in many cardiopulmonary conditions.But when was the last time any of us talked to a patient or clinical colleague about coupling?"Great news, your coupling ratio is 1.5!"Despite its common use in the literature and its ability to describe the full range of RV-PA performance, there is a surprising lack of correlation between coupling, as measured by Ees/Ea, and more clinically utilized parameters of RV dysfunction, such as RV dilation or RV ejection fraction (RVEF).This leads to an unfortunate disconnect between the research and clinical applications of RV-PA coupling.In this issue of Circulation: Heart Failure, Tello et al 5 lay out a much-needed blueprint that relates RV-PA coupling to more clinically accessible measures of RV performance in PH.In their study, they prospectively obtain pressure-volume loop measurements alongside right heart catheterization and cardiac magnetic resonance imaging in 42 human patients with PH.