Effect of potassium on supernormal conduction in the bundle branch-Purkinje system of the dog

Abstract

Experiments were performed in 14 open chest anesthetized dogs to evaluate the characteristics of supernormal conduction in the ventricular specialized conduction system during premature atrial beats. Close bipolar intramural electrodes were used to record from the bundle of His and from proximal and distal portions of the left and right bundle branch-Purkinje system. Atrial and ventricular electrograms and the surface electrocardiogram were also recorded. A period of supernormal conduction in which the conduction times of premature beats were faster than during earlier or later beats occurred throughout the bundle branch-Purkinje system in 18 of 24 cases at normal plasma potassium levels of 2.9 to 5.5 mEq/liter. The minimal conduction time during the supernormal period was decreased 8.4 ± 6.4 (standard deviation) percent below control diastolic conduction times and the supernormal period averaged 67.7 ± 31.0 msec in duration. With use of intravenous potassium infusions, plasma potassium concentration was rapidly increased from normal values up to 7.0 mEq/ liter. The magnitude of the supernormal period decreased with increasing concentrations of potassium and was eliminated at levels above 6.0 mEq/liter. The magnitude, time course, duration and potassium dependence of the period of supernormal conduction in the intact dog were comparable with those of supernormal conduction in isolated canine Purkinje tissues. It is concluded that this type of supernormal conduction in the bundle branch-Purkinje system of the intact dog must have a mechanism similar to that of supernormal conduction in the isolated tissue, which has been shown to be due to a period of supernormal excitability. The potassium dependence described for this type of supernormality may aid in identifying the mechanism for supernormality in man.