Asynchrony of Conduction within the Canine Specialized Purkinje Fiber System

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Abstract
Asynchrony of conduction may prove to be an important mechanism for reentrant arrhythmias. The purpose of these experiments was to explore asynchronous conduction in the distal branches of the canine Purkinje system. Microelectrodes were placed in Purkinje bundle preparations resembling a T configuration, thereby permitting assessment of differential conduction times induced by premature beats (S2). Equal conduction depression was observed in the post extrasystolic beat (S1 at wide coupling intervals (S2-S1). Asynchrony of conduction was frequently observed in response to narrow coupling intervals. These differential conduction times induced disparities of activation times greater than 50 msec. In fibers exhibiting preferential depressed conduction, local block was observed with further decrease in the coupling interval. Disparities of activation times at very short S2-S1 coupling times could be markedly increased by minimal decrease in coupling intervals (in the order of 1 to 5 msec). Conduction depression was not clearly dependent upon the level of "take-off" potential or action potential duration. Asynchronous conduction may thus be induced by narrow coupling of premature beats and could account for reentry.