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(Circulation. 2001;104:227.)
© 2001 American Heart Association, Inc.

Basic Science Reports

Optical Mapping of Ventricular Defibrillation in Isolated Swine Right Ventricles

Demonstration of a Postshock Isoelectric Window After Near-Threshold Defibrillation Shocks

Nina C. Wang, BA; Moon-Hyoung Lee, MD; Toshihiko Ohara, MD; Yuji Okuyama, MD; Gregory A. Fishbein, BA; Shien-Fong Lin, PhD; Hrayr S. Karagueuzian, PhD; Peng-Sheng Chen, MD

From the Division of Cardiology (N.C.W., M.-H.L., T.O., Y.O., G.A.F., H.S.K., P.-S.C.), Department of Medicine, Cedars-Sinai Medical Center and University of California–Los Angeles, Los Angeles, Calif; and Department of Physics and Astronomy (S.-F.L.), Vanderbilt University, Nashville, Tenn.

Correspondence to Peng-Sheng Chen, MD, Room 5342, Cedars-Sinai Medical Center, 8700 Beverly Blvd, Los Angeles, CA 90048. E-mail chenp{at}csmc.edu

Background—— Investigators who studied ventricular defibrillation by use of optical mapping techniques failed to observe an initial defibrillation event (isoelectric window or quiescent period) shown by electrode mapping studies. This discrepancy has important implications for the mechanisms of defibrillation. The purpose of the present study was to demonstrate an optical equivalent of an isoelectric window after a near-threshold defibrillation shock.

Methods and Results—— We studied 10 isolated, perfused swine right ventricles. Upper limit of vulnerability was determined by shocks on T waves. A 50% probability of successful defibrillation (DFT50) was determined with an up-down algorithm. Immediately after unsuccessful defibrillation shock, new wavefronts were generated. When the shock strength was low, immediate reinitiation of reentry and ventricular fibrillation might occur without a postshock isoelectric window. However, if the shock strength was within 50 V of DFT50 (near-threshold), a synchronized activation occurred, followed by organized repolarization that ended 64±18 ms after shock. After a period of quiescence (18±24 ms), activation recurred 83±33 ms after shock and reinitiated ventricular fibrillation. Similar patterns of activation, including a quiescent period, were observed after shock was applied on the T wave of the paced beat that induced ventricular fibrillation. Upper limit of vulnerability correlated well with DFT50.

Conclusions—— In isolated swine right ventricles, an optical equivalent of an isoelectric window exists after near-threshold defibrillation shocks. These findings support the idea that a near-threshold defibrillation shock terminates all activation wavefronts but fails to halt ventricular fibrillation because the same shock reinitiates ventricular fibrillation after an isoelectric window.

Key Words: action potentials • mapping • electrical stimulation • electrophysiology • death, sudden

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