A 10-year-old female Labrador retriever was presented for evaluation and management of syncope. On presentation, idioventricular tachycardia (IT) was electrocardiographically evident but neither ventricular capture nor fusion complexes were recorded. Spontaneous termination of the IT resulted in prolonged ventricular asystole and revealed the underlying rhythm of third-degree atrioventricular block. The serum concentration of troponin-I was elevated, suggesting myocarditis, but this was not diagnostically confirmed. It is likely that overdrive suppression of subsidiary idioventricular pacemakers, and perhaps also disease of subsidiary ventricular pacemaker fibers, importantly contributed to the duration of asystole.

一只 10 岁的雌性拉布拉多猎犬接受了晕厥的评估和处理。就诊时，心电图显示特发性室性心动过速 (IT)，但未记录到心室俘获和融合波群。IT 的自发终止导致心室停搏延长，并揭示了三度房室传导阻滞的潜在节律。血清肌钙蛋白-I 浓度升高，提示心肌炎，但这未得到诊断证实。辅助心室起搏器的过度驱动抑制，以及辅助心室起搏器纤维的疾病，很可能对心搏停止的持续时间有重要影响。