VENTRICULAR-FIBRILLATION AND DEFIBRILLATION THRESHOLDS IN SHEEP AND DOGS

Ventricular defibrillation studies normally use dogs rather than other large species. To investigate the suitability of sheep, which are oft en cheaper and more readily available, we compared ventricular fibrill ation and defibrillation thresholds (VFT, DFT) in sheep and dogs. A to tal of 12 sheep (31 +/- 5 kg) and six dogs (19 +/- 1 kg) were anesthet ised with halothane. Fibrillation was induced via epicardial pacing le ads, using a 1 s 50 Hz pulse. Biphasic defibrillation shocks were deli vered across epicardial patches. Voltage-response curves for both fibr illation and defibrillation were generated. Logistic regression analys is was used to determine 50 and 90% probability of success for fibrill ation induction and defibrillation. VFT was similar in sheep and dogs. DFT at 50% probability of success was significantly higher in sheep ( 369 +/- 14 V) than in dogs (299 +/- 31 V, P < 0.04) but within each sp ecies there was no correlation between heart weight and DFT. After def ibrillation sheep took longer to return to sinus rhythm than dogs and electro-mechanical dissociation was observed in sheep, but not in dogs . Thus, sheep may not be an ideal model for ventricular defibrillation research but further studies of the intrinsic differences between she ep and dogs may provide insights into basic mechanisms of defibrillati on. (C) 1998 Elsevier Science Inc. All rights reserved.