Electrophysiological effects of quinidine alone and of the combination quinidine‐verapamil on av conduction in humans

Abstract The influence of 320 mg quinidine administered intravenously (i.v.), as well as subsequent administration of 5 mg verapamil i.v. on atrioventricular conduction was studied in 8 patients during sinus rhythm and atrial stimulation with the aid of His bundle electrography. Among the electrophysiologic parameters of the atrium the sinus rate increased significantly after quinidine and again increased slightly after subsequent administration of verapamil. During sinus rhythm the PA interval was not influenced by either substance. Conversely, during atrial stimulation the STA interval increased significantly under the effect of quinidine, while verapamil had no further influence. As an indicator of conduction time in the AV node, the AH interval was decreased significantly by quinidine during sinus rhythm and atrial stimulation. This effect was significantly counteracted by the additional administration of verapamil. The HV interval as a measure of the His‐Purkinje conduction was not significantly affected. The QRS duration was increased significantly by quinidine and was not further influenced by verapamil. The QT C and QT intervals increased significantly after administration of quinidine and were again slightly, but significantly shortened by verapamil. Our investigations show that the combination of quinidine and verapamil, which has clinically been found to have a higher conversion rate than quinidine alone, is well justified from an electrophysiologic point of view and that undesirable quinidine‐related effects, such as rapid AV conduction in cases of atrial fibrillation and flutter, can be avoided by the subsequent administration of verapamil.