Electrophysiological effects of the antiarrhythmic agent QX-572 in the human heart with special reference to rate-induced changes in effective refractory periods.

The antiarrhythmic agent, N,N-bis(phenylcarbamoylmethyl)dimethylammonium chloride (QX-572) 8 mg/kg body weight produced a decreased conduction time through the atrioventricular node but did not influence intra-atrial or intraventricular conduction. Effective refractory periods of the atrium, the atrioventricular conduction system, and the ventricle were shortened by the drug. The observed effects were present at the end of drug infusion but had disapnerbd 30 min later. The probable explanation is an increased sympathetic tone induced by QX-572.