S.: Interactions of quinidine and potassium on atrioventricular transmission. Circ Res 20

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 observa-tions were made: (A) The marked prolongation of A-V conduction time pro-duced 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+ concentratio