Influence of atropine on spontaneous or catecholamine-induced arrhythmias after experimental infarction in the dog.

The effects of atropine on ventricular tachyarrhythmias induced by ligature of the anterior descending coronary artery were studied in conscious dogs. On the first day after surgery, animals received a mixture of quinidine and phenytoin orally in order to partially correct rhythm disturbances on the second day. The same animals were used on the third and fourth days after occlusion, when spontaneous regression of arrhythmias was occurring. Atropine (0.2 mg/kg i.v.) or methscopolamine (0.2 mg/kg i.v.) almost completely suppressed the ventricular arrhythmias which persisted in some animals on day 2. In animals with partially corrected tachyarrhythmias, atropine protected against aggravation of rhythm disturbances by norepinephrine and even more so against those induced by isoproterenol. The favorable effect of atropine seems to be mainly related to overdrive suppression. Atrial electrostimulation at a frequency slightly above that of the ventricular arrhythmias also normalized cardiac rhythm.