Damage in canine hearts following defibrillator shocks

Experiments were performed to investigate possible differences in potential myocardial cell damage following the use of two clinically available difibrillators. One had a damped sine wave (DSW), and the other a truncated exponential waveform (TEW). The latter, therefore, had a lower peak current and voltage. After pilot studies to determine damage potential, an energy content of 10 Joules per kg was selected with three transthoracic shocks at 30 second intervals, delivered with paddles, by both defibrillators. Thirteen dogs were shocked with DSW (10 sacrificed at 24 hours and three at 72 hours). Eleven dogs were shocked with TEW (eight sacrificed at 24 hours and three at 72 hours). Three were used as untreated controls. Observations included ECG monitoring, technetium99m pyrophosphate (Tc-PyP) uptake, and gross and microscopic observations including electron microscopy. This report will concentrate on the morphologic changes. Eleven of 13 dogs shocked with DSW developed ventricular tachycardia, transient heart block, Tc-PyP uptake and myocardial cell death with acute necrosis, and aberrant contraction patterns associated with cell death. Progression of the lesions occurred from 24 to 72 hours. Only two (one at 24 hours and one at 72 hours) of the dogs shocked with TEW showed microscopic foci of necrosis. One was a chance finding (24 hours); the other was associated with an overlying "yellow streak". In neither case were arrhythmias or Tc-PyP uptake observed. The results indicate that in dogs at equivalent energy levels, TEW caused significantly less myocardial damage than DSW.