Effects of atropine on cardiac rate and rhythm in dogs.

Changes in cardiac rate and rhythm were determined in atropinized dogs prior to, during, and after anesthetic induction with thiamylal sodium and maintenance with 1% halothane in 50% nitrous oxide and 50% oxygen. The incidence of cardiac dysrhythmias and sinus tachycardia was significantly higher prior to and after anesthetic induction in dogs given atropine, compared with dogs not atropinized. Second-degree atrioventricular block was the most frequent dysrhythmia prior to anesthetic induction in atropinized dogs. Most cardiac dysrhythmias were detected during the anesthetic induction and early maintenance periods. The most common dysrhythmias during these periods were unifocal ventricular premature depolarizations and ventricular bigeminy.