Transthoracic Ventricular Defibrillation with Triangular and Trapezoidal Waveforms

Abstract

From 7,200 fibrillation-defibrillation episodes in anesthetized dogs, the effectiveness of 6 classes of unidirectional shocks in reversing ventricular fibrillation of 30-sec duration was determined. The shocks lasted for 1 to 256 msec. Three waveforms (ascending ramp triangular, descending ramp triangular, and trapezoidal) were studied at peak currents of 10 amp and 20 amp. Families of curves of per cent success vs. energy were derived from the data for the 6 classes of waveforms studied and from corresponding curves for 3 classes of unidirectional square-wave shocks previously studied by our group. The families of curves were used as a basis for an analysis of the influence of various parameters on the effectiveness of shocks. We conclude that an appropriate energy content is a necessary, but not sufficient condition for effective ventricular defibrillation, that long, low-amplitude tails on shocks are detrimental and that excessive energy content is detrimental.ADDITIONAL KEY WORDS energy content of shock electrical stimuli fibrillation refibrillation high power amplifier closed-chest defibrillation cardiac arrhythmias anesthetized dogs

Mechanisms of superiority of ascending ramp waveforms: new insights into mechanisms of shock-induced vulnerability and defibrillation

“…As the field of clinical defibrillation matured, numerous studies were devoted to find the optimal shock waveform that would accomplish defibrillation with minimal delivered energy. It was shown that morphologically distinct waveforms have different defibrillation efficacies in both experimental studies (18,19,26,32,42) and theoretical studies using lumped models (16,43). However, the experimental studies that elucidate mechanisms for differences in defibrillation efficacies of the various waveforms are lacking.…”

“…However, previous experimental studies have already demonstrated that a monophasic ascending ramp (AR) waveform has higher defibrillation efficacy compared with the descending ramp (DR) waveform, with the rectangular waveform having an intermediate efficacy (29,32,41). Furthermore, a study using the modified Blair model demonstrated that the monophasic AR waveform has better polarization efficacy than the monophasic exponential decaying waveform (16).…”

“…In a study by Schuder et al (32), the investigators found that the defibrillation efficacies of AR and DR waveforms were similar when their durations were Ͻ10 ms, but diverged for longer durations. Whereas longer DR waveforms were less and less likely to defibrillate, AR waveforms achieved their highest defibrillation efficacy for pulse durations longer than 30 ms. Schuder et al (32) attributed the superior efficacy of longer AR waveform to a sharp fall in current at the end of the waveform. Furthermore, they argued that it was the leading portion of a DR waveform that accomplishes defibrillation and that the tail portion of the waveforms was unnecessary and may in fact be detrimental because it might reinduce fibrillation.…”

Characteristic Energy Method for Evaluation of Monopolar Defibrillation Pulse Efficiency

“…It follows from this model that trian gular ascending pulses and triangular descending pulses of the same pulse time should have the same threshold amplitude of defibrillation current and the same thresh old defibrillation energy. However, it was shown experi mentally that a triangular ascending pulse required lower defibrillation energy (lower current amplitude) compared to a triangular descending pulse [2,3].The characteristic energy method suggested in this work provides theoretical assessment of monopolar defib rillation pulse efficiency. This method allows pulses of dif ferent shape to be tested and optimal defibrillation pulse time to be determined for elucidation of this difference.…”

Analisador de desfibriladores e cardioversores.

“…A arquitetura do desfibrilador de descarga capacitiva de onda trapezoidal apresenta outra variante do desfibrilador por descarga capacitiva simples, na qual controlam-se os momentos inicial e final de descarga para evitar, por um lado, o elevado pico inicial de tensão, que geralmente ocasiona arritmias pós desfibrilatórias, além de danos ao miocárdio e, por outro lado, a suave e lentíssima descarga residual, denominada de "rabicho", que tende a refibrilar o coração [27].…”