ABSTRACT
Antiarrhythmic drugs variously can suppress premature complexes and slow or terminate a tachycardia. The traditional antiarrhythmic drug classification scheme divides drugs into four classes based on their predominant electrophysiologic effect on cardiac action potentials. The kinetics of channel binding and dissociation vary for different class I drugs, which likely explains in part their efficacy against specific rhythm disturbances. Lidocaine hydrochloride generally is the agent of first choice for acute therapy of ventricular tachyarrhythmias in dogs. It is used in cats and horses as well. Lidocaine usually is ineffective against supraventricular arrhythmias; however, it might induce conversion of recent onset, vagally mediated atrial fibrillation or supraventricular tachycardia (SVT) in some dogs, especially those with macro-reentrant SVT associated with an accessory pathway. Procainamide is well-absorbed orally in dogs although food may delay absorption. A related drug, disopyramide, is available but causes significant myocardial depression, and mainly is used in humans to treat hypertrophic obstructive cardiomyopathy.
