Defibrillation and the upper limit of vulnerability to fibrillation in a transthoracic guinea pig model

Recent studies have shown sustained tachyarrhythmias in guinea pigs. We hyp othesized that guinea pigs could be used as a model of ventricular fibrilla tion, focusing on defibrillation waveform efficacy and the upper limit of v ulnerability to fibrillation. In 10 male guinea pigs, an esophageal/apical pacing electrode configuration was used. The electrocardiogram (ECG) and ar terial blood pressure were continuously monitored. T-wave and defibrillatio n shocks were applied transthoracically. A modified up-down protocol was us ed. After up-down testing was completed, a tachyarrhythmia was induced with out electrical termination. All animals died of a sustained tachyarrhythmia . The monophasic DFT50 (the 50% successful defibrillation voltage, 496 +/- 176 V) was larger than the biphasic DFT50 (364 +/- 94 V, P < .005). The upp er limit of vulnerability to fibrillation (ULV50) (the 50% successful induc tion voltage) was correlated with the DFT50 for both monophasic (r = .82, P < .005) and biphasic shocks (r = .88, P < .005). Its low cost and ease of handling may make the guinea pig a preferred model for some fibrillation an d defibrillation studies.