Pericardial effusion increases defibrillation energy requirement

Pericardial effusion may increase defibrillation energy requirements. We examined the effect of pericardial effusion in seven pentobarbital anesthetized dogs (25.3 +/- 3.4 kg) using monophasic and biphasic shock. A median sternotomy was performed and two 13.9 cm2 patch electrodes were sewn extrapericardially; 3 cc/kg of 0.9% NaCl was instilled through an intrapericardial catheter used to create a hemodynamically insignificant pericardial effusion. Four trials of five leading edge voltages (200-600 volts, in 100 volt increments) were performed for monophasic and biphasic shocks of 10 msec total duration and defibrillation efficacy curves were determined by logistic regression analysis. Baseline impedance was 68.1 and 66.2 Ohms for monophasic and biphasic waveforms, respectively, and decreased to 52.9 and 49.9 Ohms, respectively, with pericardial effusion (P < 0.01). Energy associated with 80% probability of successful defibrillation (E80) for monophasic shock was 16.0 joules at baseline and increased to 18.5 joules with pericardial effusion (P < 0.016). Similarly, E80 for biphasic shocks increased from 10.6 joules to 13.0 joules (P < 0.016). Removal of pericardial effusion was associated with impedance and E80 returning to baseline. In this model, pericardial effusion increased defibrillation energy requirements and may explain early postimplant defibrillator failure.