Coronary occlusion site as a determinant of the cardiac rhythm effects of atropine and vagotomy.

We have previously demonstrated that atropine pretreatment increases the incidence of fatal ventricular arrhythmias induced by left anterior descending coronary artery (LAD) occlusion. The purpose of the present study was to determine whether the deleterious effect of atropine also applies to arrhythmias induced by right coronary artery (RCA) occlsusion. Occlusion of the RCA resulted in ventricular arrhythmias in all 20 animals studied, followed by ventricular fibrillation in three animals (15 per cent). Right coronary occlusion also resulted in bradycardia (-30.3 +/- 5.1 beats per minute) and hypotension (-23.1 +/- 4.9 mm. Hg). Pretreatment of 15 animals with atropine caused no significant increase in the incidence of ventricular fibrillation (i.e., 20 per cent). In addition, atropine pretreatment had no effect on the fall in heart rate and hypotension associated with RCA ligation. Sectioning the vagus nerves produced results similar to atropine pretreatment with the exception that a significant portion of the bradycardia was prevented. These results indicate that the increase in deaths after atropine observed in animals undergoing experimental LAD occlusion in not demonstrated with RCA occlusion. The results also indicate that the potential for deleterious effects of atropine in acute infarction might depend on the anatomic location of the involved myocardium.