Volume Calibration with Cardiac MRI vs Hypertonic Saline for Right Ventricular Pressure-Volume Loops with Exercise: Impact on ventricular function and ventricular-vascular coupling.

Right ventricular (RV) pressure-volume (PV) loops require post-acquisition volume calibration by cardiac MRI (CMR) or hypertonic saline (HS). We defined the impact of these two volume calibration methods on rest-to-exercise ventricular contractility (end-systolic elastance: Ees), arterial afterload (Ea) and coupling (Ees/Ea). In a prospective study, 82 RV PV-loop datapoints (rest, exercise stages-every 25watts and recovery) and CMR were acquired in 19 participants. In comparison to CMR, HS-based calibration over-estimated RV end-systolic volume at rest, mean (SD) by +38 mL (48) and end-diastolic volume by +46 mL (68), resulting in underestimated RVEF by -8%. However, Ees and Ea were similar at rest (r²=0.76 and 0.71 respectively, p<0.001 for both) and Ees:Ea was identical (r²=1.00, p<0.001). Exercise metrics also remained similar: RV reserve (ΔEes) and change in coupling (ΔEes/Ea). In comparison to CMR (gold-standard), HS-based calibration under-estimates RVEF at rest, however it is a robust approach for measuring coupling and RV reserve.