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(Circulation. 1974;49:858.)
© 1974 American Heart Association, Inc.

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Patterns of Ventricular Activity During Catheter Defibrillation

MORTON M. MOWER M.D.¹; M. MIROWSKI M.D.¹; JOSEPH F. SPEAR PH.D.¹; E. NEIL MOORE D.V.M., PH.D.¹

¹ From the Department of Medicine, Sinai Hospital of Baltimore; the Departments of Medicine and Pediatrics, The Johns Hopkins University School of Medicine, Baltimore, Maryland; the Comparative Cardiovascular Studies Unit, School of Veterinary Medicine, and Department of Medicine, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.

In order to clarify the mechanism of ventricular catheter defibrillation in which the electrode distribution and the low energy requirements make a simultaneous depolarization of the entire myocardium unlikely, the electrocardiograms recorded during 120 catheter fibrillation-defibrillation episodes in 39 dogs were analyzed. Three distinct, equally distributed defibrillation patterns were observed: 1) immediate resumption of a coordinated rhythm, thought to reflect complete depolarization of the myocardium; 2) increasing coarsening of the fibrillation waveforms interpreted as progressive reduction in the number of fibrillating fibers with reversion when a critical mass of myocardium with synchronized activity is reached, and 3) production of more coordinated "flutter-like" ventricular complexes probably representing a rhythm distinct from fibrillation and convertible to sinus rhythm by a second subthreshold shock. These observations suggest that total depolarization of the entire myocardium is not a prerequisite for ventricular defibrillation.

Key Words: Low-energy defibrillation • Multiple mechanisms of defibrillation • Catheter countershock • Critical mass for ventricular defibrillation

Submitted on December 17, 1973
Accepted on January 21, 1974

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