The efficacy and safety of external biphasic defibrillation in toy breed dogs

Objective: To evaluate the efficacy and safety of biphasic (BP) defibrillation in toy breed dogs (< 5 kg of body weight). Design: Prospective, clinical experimental study. Setting: Veterinary teaching hospital. Animals: Five dogs (pilot study) and 10 dogs (comparison study of biphasic versus monophasic defibrillation). Measurements and main results: The efficacy of defibrillation was compared by estimating E80 (80% probability of successful defibrillation) after biphasic (BP) and monophasic (MP) defibrillations. The E80 for BP defibrillation was 7.24 +/- 1.33 J (2.24 +/- 0.41 J/kg) and 10.24 +/- 1.34 J (3.18 +/- 0.12 J/kg) for MP defibrillation. BP waveform required 30% less shock energy for a successful defibrillation. In order to compare the safety of defibrillation, we evaluated changes in cardiac biomarkers, electrocardiogram, echocardiographical left ventricular index, and aortic pressure during and after BP and MP defibrillation. All dogs treated by either BP or MP defibrillation survived. Pulseless electrical activity occurred in 2 of 5 dogs during MP defibrillation. The levels of cardiac biomarkers were elevated and sustained for longer periods in the MP defibrillation group. Electrocardiographic changes (e.g., QT prolongation, the time to return to an isoelectric ST segment after shocks) were more severe and longer in the MP defibrillation group. In addition, overall left ventricular cardiac performance was severely depressed in the MP group compared with the BP group. Conclusion: Our findings suggest that BP defibrillation is more effective and safer than MP defibrillation. We determined the acceptable shock energy to be 2-4 J/kg for toy breed dogs.