Influence of Atropine and of Vagally Mediated Bradycardia on the Occurrence of Ventricular Arrhythmias following Acute Coronary Occlusion in Closed-Chest Dogs

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Abstract
In contrast to previous opinions, recent investigations have suggested that increasing heart rate (HR) with atropine when moderate sinus bradycardia accompanies acute myocardial infarction is not necessarily beneficial. To further characterize the influence of vagally mediated changes in HR during ischemia, we evaluated the effects of atropine and of electric stimulation of the vagus nerves on the incidence of ventricular arrhythmias during acute coronary occlusion in closed-chest dogs. Protection from occlusion-induced arrhythmia was not observed when 28 dogs receiving atropine were compared with 27 control dogs. Rather, the total incidence of ventricular arrhythmias was significantly higher (P < 0.05) and ventricular fibrillation tended to occur more frequently in the atropine-treated group. Moreover, fewer ventricular arrhythmias (and total absence of ventricular fibrillation or close-coupled premature beats) were noted in 12 control animals with spontaneous bradycardia (HR<60 beats/min) compared with ...