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Factors Related to the Induction of Ventricular Fibrillation in the Normal Canine Heart by Programmed Electrical Stimulation

By Angas W. Hamer, Hrayr S. Karagueuzian, Kaoru Sugi, Carol A. Zaher, William J. Mandel and Thomas Peter

Abstract

Programmed electrical stimulation was performed in eight normal dogs using a stimulator and endocardiai electrode catheters identical to those used in human studies. The right and left ventricular apex were paced at a drive cycle length of 400 ms and, in some cases, 500 ms, with a pacing sequence of single (S1S2), double (S1S2S3) and triple (S1S2S3S4) premature impulses introduced after eight paced complexes. Pacing sequences were performed using combinations of pulse width (1, 2 and 4 ms) and current strengths of 2, 5 and 10 times diastolic threshold, and in three dogs, 15 times diastolic threshold.Twenty-two episodes of ventricular fibrillation were initiated in five dogs in 170 pacing sequences using current strengths up to 10 times diastolic threshold, and six episodes of ventricular fibrillation in the two of three remaining dogs tested at 15 times diastolic threshold. Ventricular fibrillation was reproducible on seven of nine occasions. Ventrieular fibrillation was never induced by S1S2at up to 15 times diastolic threshold; it was induced by S1S2S3in 3 (1.8%) of 170 sequences, but only at 10 times diastolic threshold. It was induced by S1S2S3S4in 19 (11.4%) of 167 sequences using 2 to 10 times diastolic threshold, although 20 of 28 episodes only occurred with S1S2S3S4at 10 or more times diastolic threshold. Induction of ventricular fibrillation was not related to pulse width, but when sequences using S1S2S3S4at 10 times diastolic threshold were examined, ventricular fibrillation was related to the shortness of the coupling intervals of the premature stimuli (S1S2+ S2S3+ S3S4: ventricular fibrillation = 367 ± 26 ms, no ventricular fibrillation = 417 ± 41 ms, p < 0.001). Current strength appeared to have some independent role, occasionally causing ventricular fibrillation at 10 times but not at 5 times diastolic threshold at similar coupling intervals.It is concluded that spurious ventricular fibrillation is unlikely to be initiated in the normal canine ventricle by S1S2at up to 15 times diastolic threshold, or by S1S2S3at less than 10 times diastolic threshold. S1S2S3S4appeared capable of initiating ventricular fibrillation at any current strength, with maximal frequency at 10 times diastolic threshold or greater. These findings allow better assessment of the significance of arrhythmias induced by these pacing methods in abnormal canine hearts, and demonstrate some principles that may be applicable to human studies

Publisher: American College of Cardiology Foundation. Published by Elsevier Inc.
Year: 1984
DOI identifier: 10.1016/S0735-1097(84)80251-X
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