Beneficial Effects of Vagal Stimulation and Bradycardia During Experimental Acute Myocardial Ischemia

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Abstract
It is commonly believed that vagally-mediated bradycardia predisposes to ventricular fibrillation (VF) during acute myocardial ischemia. Recent experimental studies, however, have shown that bradycardia and vagal stimulation independently raise the threshold for electrically induced VF in the ischemic canine heart. To determine the influence of vagal stimulation on the spontaneous development of VF occurring during acute myocardial ischemia, open-chest dogs with acute coronary occlusion were observed with and without electrical vagal stimulation. When heart rate was allowed to fall, mean time to VF was 14.7 ± 2.1 min (se) in the control dogs (heart rate about 180/min), 23.4 ± 1.9 (P < 0.01) in the dogs with low intensity vagal stimulation (heart rate about 100/min), and 28.6 ± 0.9 (P < 0.001) in dogs with high intensity vagal stimulation (heart rate about 60/min). Only 10% of the control animals survived after 30 min of occlusion compared with 40% (NS) of the dogs with low intensity vagal stimulation and ...