Optical mapping of ventricular defibrillation in isolated swine right ventricles - Demonstration of a postshock isoelectric windrow after near-threshold defibrillation shocks

Background-Investigators who studied ventricular defibrillation by use of o ptical mapping techniques failed to observe an initial defibrillation event (isoelectric window or quiescent period) shown by electrode mapping studie s. This discrepancy has important implications for the mechanisms of defibr illation, The purpose of the present study was to demonstrate an optical eq uivalent of an isoelectric window after a near-threshold defibrillation sho ck. Methods and Results-We studied 10 isolated, perfused swine right ventricles . Upper limit of vulnerability was determined by shocks on T waves. A 50% p robability of successful defibrillation (DFT50) was determined with an up-d own algorithm. Immediately after unsuccessful defibrillation shock, new wav efronts were generated. When the shock strength was low, immediate reinitia tion of reentry and ventricular fibrillation might occur without a postshoc k isoelectric window. However, if the shock strength was within 50 V of DFT 50 (near-threshold), a synchronized activation occurred, followed by organi zed repolarization that ended 64 +/- 18 ms after shock. After a period of q uiescence (18 +/- 24 ms), activation recurred 83 +/- 33 ms after shock and reinitiated ventricular fibrillation. Similar patterns of activation, inclu ding a quiescent period, were observed after shock was applied on the T wav e of the paced beat that induced ventricular fibrillation, Upper limit of v ulnerability correlated well with DFT50, Conclusions-In isolated swine right ventricles, an optical equivalent of an isoelectric window exists after near-threshold defibrillation shocks. Thes e findings support the idea that a near-threshold defibrillation shock term inates all activation wavefronts but fails to halt ventricular fibrillation because the same shock reinitiates ventricular fibrillation after an isoel ectric window.