Effect of atropine and of chronic A-V block on coronary blood flow in the dog

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Abstract
Coronary sinus blood flow was measured by the nitrous oxide desaturation method in mongrel dogs under several experimental conditions. Observations were made in each of these conditions before and after the administration of atropine. Intravenous atropine markedly increases coronary sinus blood flow and heart rate in normal dogs but has no effect following acute bilateral cervical vagotomy. Atropine increases the coronary sinus blood flow to a moderate degree with no change in ventricular rate, in chronic A-V block dogs. Chronic A-V block does not change coronary sinus blood flow but increases calculated left ventricular efficiency. Chronic A-V does not produce congestive heart failure under conditions of somewhat restricted physical activity. Effects of atropine on coronary sinus flow are believed to be mediated through vagal fibers controlling heart rate. In the case of A-V block animals where the ventricular rate is constant the increased coronary flow may be due in part to the increase in atrial rate.