Cardiac Arrhythmias Simulated by Concealed Bundle of His Extrasystoles in the Dog

Abstract

In 10 open-chest intact dog hearts, multiple close bipolar electrograms were obtained from various regions of both atria and the bundle of His. The bundle of His was also prematurely stimulated at varying coupling intervals following a sinus beat. At short coupling intervals, the bundle of His stimulus failed to propagate antegradely (no ventricular response) but did propagate retrogradely. Coupled bundle of His stimuli retrogradely concealed within the A-V node caused the next sinus impulse to be delayed or blocked. Types I and II second degree A-V block, 2:1 A-V block, and alternation of the P-R interval were simulated. An atrial (nonconducted) bigeminal rhythm was simulated when the bundle of His stimuli completely traversed the A-V node and completely (inverted P waves) or partially (fusion P waves) depolarized the atria.