How to incorporate tricuspid regurgitation in right ventricular-pulmonary arterial coupling

Adaptation of the right ventricle (RV) to a progressively increasing afterload is one of the hallmarks of pulmonary arterial hypertension (PAH). Pressure-volume loop analysis provides measures of load-independent RV contractility, i.e., end-systolic elastance, and pulmonary vascular properties, i.e., effective arterial elastance (E-a). However, PAH-induced RV overload potentially results in tricuspid regurgitation (TR). TR makes RV eject to both PA and right atrium; thereby, a ratio of RV end-systolic pressure (P-es) to RV stroke volume (SV) could not correctly define Ea. To overcome this limitation, we introduced a two-parallel compliance model, i.e., E-a = 1/(1/E-pa + 1/E-TR), while effective pulmonary arterial elastance (E-pa = P-es/PASV) represents pulmonary vascular properties and effective tricuspid regurgitant elastance (E-TR) represents TR. We conducted animal experiments to validate this framework. First, we performed SV analysis with a pressure-volume catheter in the RV and a flow probe at the aorta in rats with and without pressure-overloaded RV to determine the effect of inferior vena cava (IVC) occlusion on TR. A discordance between the two techniques was found in rats with pressure-overloaded RV, not in sham. This discordance diminished after IVC occlusion, suggesting that TR in pressure-overloaded RV was diminished by IVC occlusion. Next, we performed pressure-volume loop analysis in rats with pressure-overloaded RVs, calibrating RV volume by cardiac magnetic resonance. We found that IVC occlusion increased E-a, suggesting that a reduction of TR increased E-a. Using the proposed framework, Epa was indistinguishable to E-a post-IVC occlusion. We conclude that the proposed framework helps better understanding of the pathophysiology of PAH and associated right heart failure.