Experimental bigeminal arrhythmia in the dog

Abstract

Ventricular bigeminal rhythm was successfully induced in 26 of 34 vagotomized dogs. Induction was accomplished through bilateral carotid artery occlusion, constriction of the thoracic aorta, or a combination of both. The following observations were made:o1.This arrhythmia appears to depend on some combination of high systemic arterial pressure and increased heart rate. It can be induced under conditions in which sympathetic discharge to the heart is inhibited.2.Sinoatrial firing rate during the bigeminal rhythm is usually regular. The PR interval is always shorter and QRS duration longer in the abnormal complex of a bigeminal pair.3.Delta waves are commonly present in the initial portion of QRS complexes of abnormal beats. These complexes have the general characteristics associated with ventricular pre-excitation (WPW).4.Mean frontal QRS vector angles in normal beats of bigeminal pairs were in the range of 23°–76°. Vector angles for abnormal mean frontal QRS complexes were widely distributed in a range of 137°–357°.5.The experimental data do not provide a positive basis for classifying the abnormal complexes as ventricular pre-excitation or coupled late ventricular ectopic beats. In either case, it appears that the site of initial ventricular activation in abnormal complexes is widely dispersed in this group of animals. This arrhythmia appears to depend on some combination of high systemic arterial pressure and increased heart rate. It can be induced under conditions in which sympathetic discharge to the heart is inhibited. Sinoatrial firing rate during the bigeminal rhythm is usually regular. The PR interval is always shorter and QRS duration longer in the abnormal complex of a bigeminal pair. Delta waves are commonly present in the initial portion of QRS complexes of abnormal beats. These complexes have the general characteristics associated with ventricular pre-excitation (WPW). Mean frontal QRS vector angles in normal beats of bigeminal pairs were in the range of 23°–76°. Vector angles for abnormal mean frontal QRS complexes were widely distributed in a range of 137°–357°. The experimental data do not provide a positive basis for classifying the abnormal complexes as ventricular pre-excitation or coupled late ventricular ectopic beats. In either case, it appears that the site of initial ventricular activation in abnormal complexes is widely dispersed in this group of animals.