Abstract
Biphasic truncated exponential (BTE) wavefoms are generated by all modem implantable cardioverter defibrillators (ICDs), and are now being implemented in tmnsthoracic defibrillators. Not all BTE waveforms are the same; therefore we compared the efficacy of 2 commercial transthoracic defibrillators. A Physio-Control (PC) Lifepak 12 and a Medical Research Labs (MRL) PIC were compared in a canine model of both normal and higher impedance patients. Methods: Animals were anesthetized and adhesive defibrillating electrode pads were placed on the shaved left and right chest walls. Ventricular fibrillation (VF) was induced with 60 Hz current, and allowed to persist for 10 seconds. The ED50 peak current and energy were estimated with an up-down protocol, and logistic regression analysis. In group 1, canines (n=6, 61.6&5.5 Ibs) were tested without any added series resistance. In group 2, canines (n=6, 53.7&6.1 Ibs) were tested with a 32 ohm resistor added in series to simulate higher impedance patients. Results: Mean ED50 peak current and energy estimates are shown in the table below. MRL BTE mean peak current was lower than PC BTE in both groups (p < 0.001). The mean ED50 delivered energy for the MRL BTE and PC BTE were not different (p = ns). Mean impedance for group 1 was 55.3 ohms, and for group 2 (including added series resistance) was 94 ohms.
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