Hypothermic facilitation of retrograde V-A conduction

¹ Department of Physiology, Baylor University College of Medicine, Houston, Texas

At normal temperatures, retrograde or V-A conduction was found in 13 of 22 dogs anesthetized with pentobarbital. R-P intervals were universally longer than P-R intervals at the same heart rate. On cooling the animals, retrograde conduction appeared in eight of the nine animals that failed to exhibit it at normal temperatures, and the R-P interval in all animals shortened as cooling progressed. In some instances R-P was shorter than P-R at comparable rates. When the ventricles were fibrillated, an irregular atrial tachycardia developed; in one experiment the rate was comparable to the ventricular rate in atrial fibrillation. The relationship was demonstrated between the Wenckebach phenomenon and the reentry or echo phenomenon. Reentry was related to a hypothecated differential effect of repetitive firing on recovery cycles within the A-V node-bundle system, the superior portion becoming progressively longer, the inferior shorter. As this continued, a stage would occur when the inferior system could be stimulated by the repolarization potential of the superior portion.