Affiliation:
1. From the Department of Medicine, Division of Cardiology, University of Maryland School of Medicine, Baltimore Md.
Abstract
Background
One of the basic characteristics of electrical defibrillation is the strength-duration relationship, or the effect of pulse width on defibrillation efficacy. This relationship is important for understanding the mechanism of defibrillation and for the design of optimal waveforms. However, a detailed evaluation of the strength-duration relationship for human transvenous defibrillation has not been performed previously.
Methods and Results
This was a prospective study of 29 patients undergoing initial defibrillator implantation with a uniform dual coil, transvenous lead. In each patient defibrillation thresholds were measured for either short (2, 3, 4, 6 ms) or long (6, 12, 18 ms) pulse durations, with the order of testing randomized. The shock waveform was a truncated monophasic pulse from a capacitor of 150 μF. The leading edge voltage at defibrillation threshold was 566±100 V for 2-ms pulses. Voltages declined exponentially with increasing pulse width reaching an asymptote by 6 ms (451±68 V,
P
<.05). Defibrillation threshold voltage was insensitive to longer pulse widths. Stored energy at defibrillation threshold showed a similar relationship with pulse width. In contrast, mean current decreased monotonically over the full range of pulse durations evaluated, and there was no evidence of a rheobase.
Conclusions
The shape of the strength-duration curve and the lack of rheobase current indicate a fundamental difference between cardiac stimulation and defibrillation. The relationship between pulse duration and defibrillation threshold voltage or stored energy is well modeled by a parallel capacitor resistor circuit with a time constant of 5.3 ms.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine
Cited by
25 articles.
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