Beneficial Effects of Amiodarone Pretreatment on Early Ischemic Ventricular Arrhythmias Relative to Infarct Size and Regional Myocardial Blood Flow in the Conscious Dog

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Abstract
The effects of chronic pretreatment with amiodarone on ischemic ventricular arrhythmias were evaluated in fully conscious instrumented dogs. In control dogs (n = 14) with large myocardial infarcts, early (first 30 min) ventricular arrhythmias occurred in a bimodal distribution with peaks at 3-5 min and at 12-25 min, with only the former associated with epicardial conduction delay. Ventricular fibrillation occurred equally frequently during each peak of early ventricular arrhythmias. Amiodarone (30 mg/kg daily) for 3-4 weeks had no significant effect (n = 11) on anatomic infarct size (28 +/- 6 vs. 30 +/- 5% of left ventricular weight) nor on collateral blood flow in the center of the infarct (19 +/- 11 vs. 15 +/- 7 ml/min/100 g of tissue) or on the ratio of endocardial/epicardial perfusion (0.23 +/- 0.19 vs. 0.28 +/- 19). Despite significant lengthening of peak epicardial conduction delay (191 +/- 20 to 239 +/- 81 ms, p less than 0.05), the frequency of early ventricular arrhythmias, especially during the second peak of ectopic activity, were markedly attenuated by amiodarone pretreatment, with the extrasystole-free intervals often being as long as 6 h. The incidence of ventricular fibrillation was 9% in the treated animals compared with 29% in the controls. In the control animals, arrhythmias always supervened when epicardial fractionation was significant, and no ectopy-free interval was present in the first 6 h following coronary occlusion. The data indicate that chronic amiodarone pretreatment exerts a beneficial effect on the frequency and severity of such ventricular tachyarrhythmias, with reduction in the incidence of ventricular fibrillation and ectopic activity in the early phases following coronary occlusion.

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