Volume calibration with cardiac MRI versus hypertonic saline for right ventricular pressure-volume loops with exercise: Impact on ventricular function and ventricular-vascular coupling.

Background: Right ventricular (RV) pressure-volume (PV) loops require postacquisition volume calibration by cardiac MRI (CMR) or hypertonic saline (HS). We defined the impact of these 2 volume calibration methods on rest-to-exercise ventricular contractility (end-systolic elastance: Ees), arterial afterload (Ea), and coupling (Ees/Ea).

Methods: In a prospective study, 82 RV PV-loop datapoints (rest, exercise stages every 25 W, and recovery) and CMR were acquired in 19 participants.

Results: In comparison to CMR, HS-based calibration overestimated RV end-systolic volume at rest, mean (SD) by +38 ml (48) and end-diastolic volume by +46 ml (68), resulting in underestimated right ventricular ejection fraction (RVEF) by -8%. However, Ees and Ea were similar at rest (r = 0.76 and 0.71, respectively, p < 0.001 for both), and Ees:Ea was identical (r = 1.00, p < 0.001). Exercise metrics also remained similar: RV reserve (ΔEes) and change in coupling (ΔEes/Ea).

Conclusions: In comparison to CMR (gold-standard), HS-based calibration underestimates RVEF at rest; however, it is a robust approach for measuring coupling and RV reserve.