Truncated Biphasic Pulses for Transthoracic Defibrillation

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Abstract
Background Early defibrillation is the single most important factor for improving out-of-hospital ventricular fibrillation resuscitation rates. To achieve the earlier response times required for survival, typically Methods and Results We prospectively and randomly compared the transthoracic defibrillation efficacy of two different truncated biphasic waveforms, 115 J (70 μF) and 130 J (105 μF), with that of a standard 200-J (36-μF, 28-mH) damped sine wave pulse using right anterior and left lateral thoracic pads (R2 Medical Systems) in 30 cardiac arrest survivors during transvenous ICD surgery. The right anterior patch electrode was used as the cathode and the left lateral thoracic pad as the anode. Transthoracic ventricular defibrillation rescue shocks were tested after a failed transvenous defibrillation shock delivered in the course of ICD testing. Each of the three different rescue shocks was tested in random order in each patient. All shocks were delivered at end expiration. The investigators responsible for determining transthoracic shock efficacy were blinded throughout the study to the transthoracic rescue waveform used. A total of 33 patients were considered for study, but three patients failed to satisfy all entry criteria or did not have a sufficient number of ventricular fibrillation inductions to allow for testing of all three waveforms. Percent efficacy for the three waveforms was then compared in the 30 patients who satisfied entry criteria and completed the protocol. The study population had a mean age of 61±11 years, with 22 (73%) being men. The mean left ventricular ejection fraction was 0.39±0.14. Coronary artery disease was present in 22 (73%). The 115-J (70-μF) biphasic pulse, the 130-J (105-μF) biphasic pulse, and the 200-J (36-μF, 28-mH) damped sine wave pulse were equally effective, resulting in a 97% first-shock ventricular defibrillation efficacy rate. Each waveform failed to defibrillate once, with each waveform failing in a different patient. Conclusions The results of this study suggest that biphasic truncated transthoracic shocks of low energy (115 and 130 J) are as effective as 200-J damped sine wave shocks used in standard transthoracic defibrillators. This finding may contribute significantly to the miniaturization and cost reduction of transthoracic defibrillators, which could enable the development of a new generation of AEDs appropriate for an expanded group of out-of-hospital first responders and, eventually, layperson use.