Abstract 401: Shortening of Action Potential Duration With Increased Work in Contracting Rabbit Heart

Abstract

Studying heart function in contracting hearts at higher workloads provides crucial knowledge of cardiac performance in high-stress situations. Ratiometric optical mapping of fully loaded hearts is a novel method to study electrical activity while replicating in vivo energy consumption. We predict that an imbalance between energy supply and demand during increased work and hypoxia will manifest in shortened action potential duration (APD), especially in the more physiologically-relevant bi-ventricular (BiV) working heart. Rabbit hearts were perfused with oxygenated Krebs-Henseleit solution in unloaded Langendorff and fully-loaded BiV mode. Epicardial action potentials (APs) were measured using optical mapping of Di-4-ANEPPS. Excitation ratiometry using 450 and 505 nm illumination on alternate camera frames together with motion tracking removed motion artifact. Aortic pressure, left atrial preload, and LVDP was measured. A range of workloads were studied by pacing at 330, 220, and 170 ms cycle length (CL). Gradual hypoxia was induced by bubbling with N2 gas. In Langendorff mode, the APD was 137.67±4.29 ms, 113.44±7.89 ms, and 106.44±0.44 ms at CL of 330ms, 220ms, and 170ms, respectively, while in BiV mode, the APD was 106.56±13.03 ms, 78.00±2.33 ms, and 69.33±0.77 ms. Aortic pressure dropped from NSR in BiV hearts by 1.26% at 330ms, 4.11% at 220ms, and 11.65% at 170ms CL. Shortening of APD, independent of restitution, with increasing HR indicates an imbalance of energy supply and demand with greater workload. KATP channels are implicated. This novel method of optical mapping reveals important implications of electrophysiological changes during high-stress situations.