PROSPECTIVE RANDOMIZED COMPARISON OF ANODAL MONOPHASIC SHOCKS VERSUS BIPHASIC CATHODAL SHOCKS ON DEFIBRILLATION ENERGY-REQUIREMENTS

Biphasic shocks are believed to be superior to monophasic shocks, Mono phasic anodal shocks, as opposed to cathodal shocks, are associated wi th improved defibrillation energy requirements (DERs). However, it is unclear how the DER of anodal monophasic shocks compare with conventio nal biphasic shocks. Therefore the purpose of this study was to prospe ctively compare the DER of an anodal monophasic shock with that of a c athodal biphasic shock. A transvenous defibrillation lead with distal and proximal shocking electrodes was used. The subjects of this study were 20 consecutive patients with a mean age of 64.2 +/- 10.5 years (/-SD) and a mean left ventricular ejection fraction of 0.36 +/- 0.18. Six had had cardiac arrest. The DER, defined as the lowest energy that converted ventricular fibrillation to sinus rhythm, was determined tw ice with a step-down protocol (25 J, 20 J, 15 J, 10 J, 5 J, 3 J, 1 J). If the DER was greater than or equal to 25 J, then a subcutaneous pat ch was deemed necessary for system implantation. In random order the D ER was determined with a monophasic anodal shock (distal electrode pos itive) and then with a cathodal (first phase, distal electrode negativ e) biphasic shock. The mean DER with anodal monophasic shocks was 15.1 +/- 8.5 J compared with 13.6 +/- 8.1 J with cathodal biphasic shocks (p = 0.4). A DER greater than or equal to 25 J was present in three pa tients with the monophasic waveform and in three patients with the bip hasic waveform (p = NS). In conclusion, the DER and frequency of subcu taneous patch use with an anodal monophasic waveform is comparable to that obtained with a cathodal biphasic waveform.