Interactions of Quinidine and Potassium on Atrioventricular Transmission

Abstract

The effects of quinidine and its interactions with potassium (K) on atrio-ventricular (A-V) conduction were studied in isolated, perfused rabbit hearts, utilizing microelectrode techniques. Quinidine gluconate (10 mg/liter) was added to perfusion fluid containing either normal [K + ] (4.5 mEq/liter), low [K + ] (1.5 mEq/liter), or high [K + ] (7.5 mEq/liter). The following observations were made: (A) The marked prolongation of A-V conduction time produced by quinidine was antagonized by low K + and enhanced by high K + concentration. (B) Quinidine or high K + concentration prolonged the A-V interval by slowing intra-atrial and His-Purkinje-ventricular conduction. (C) Low K + concentration depressed conduction in the N region of the A-V node. (D) Lowering K + concentration in the presence of quinidine shortened the A-V interval by enhancing His-Purkinje-ventricular conduction. (E) Quinidine and high K + concentration increased the action potential amplitude in the nodal and the node-His regions of the A-V node while low K + concentration showed opposite effects. Hence, different regions of the A-V conducting system were selectively influenced by these agents. A-V conduction in the presence of low K + and quinidine depends upon the net results of their antagonism within individual fiber types. The importance of these interrelationships in pharmacologic approach to A-V conduction disturbances is stressed.