Noninvasive Pressure-Volume Loops using the Elastance Model and CMR – A Porcine Validation at Transient Preloads

Abstract

Pressure-volume (PV) loops have utility in evaluation of cardiac pathophysiology but require invasive measurements. Recently, a time-varying elastance model to derive PV loops noninvasively was proposed, using left ventricular (LV) volume by cardiovascular magnetic resonance (CMR) and brachial cuff pressure as inputs. Validation was performed using CMR and pressure measurements acquired on the same day, but not simultaneously, and without varying preload. This study validate the noninvasive elastance model used to estimate PV loops at varying preloads, compared with simultaneous measurements of invasive pressure and volume from real-time CMR, acquired concurrent to an inferior vena cava (IVC) occlusion. We performed dynamic PV loop experiments under CMR-guidance in 15 pigs (n = 7 naïve, n = 8 with ischemic cardiomyopathy). Preload was altered by IVC occlusion while simultaneously acquiring invasive LV pressures and volumes from real-time CMR. Pairing pressure and volume signals yielded invasive PV loops, and model-based PV loops were derived using real-time LV volumes. Hemodynamic parameters derived from invasive and model-based PV loops were compared. Across 15 pigs, 323 PV loops were recorded. Intraclass correlation coefficient (ICC) agreement was excellent between model-based and invasive stroke work (bias = 0.007 ± 0.03J, ICC = 0.98), potential energy (bias = 0.02 ± 0.03J, ICC = 0.99), ventricular energy efficiency (bias = -0.7 ± 2.7%, ICC = 0.98), contractility (bias = 0.04 ± 0.1 mmHg/ml, ICC = 0.97), and ventriculoarterial coupling (bias = 0.07 ± 0.15, ICC = 0.99). All hemodynamic parameters differed between naïve and cardiomyopathy animals (p < 0.05). Invasive vs model-based PV loop dice similarity coefficient was 0.88 ± 0.04. An elastance model-based estimation of PV loops and associated hemodynamic parameters provided accurate measurements at transient loading conditions compared with invasive PV loops.