Biomedical subjects

H D Beekman

Publications and source records attributed to H D Beekman.

3 recordsLinked to original sources

PubMed1987

Triggered activity induced by pacing during digitalis intoxication: observations during programmed electrical stimulation in the conscious dog with chronic complete atrioventricular block.

In isolated Purkinje fibers, digitalis intoxication induces triggered activity, which is based upon delayed afterdepolarizations. The characteristics of delayed afterdepolarizations have been studied systematically by programmed electrical stimulation. The present investigations were done to study the role of triggered activity during digitalis intoxication in the intact heart. For this purpose, a pacing protocol, similar to that used in experiments of isolated Purkinje fibers, was used. The experiments were done on conscious dogs with chronic complete atrioventricular block. Ventricular tachycardia was induced with digoxin IV 0.1 mg/kg/1-1 1/2 hr. The effect of programmed electrical stimulation on the first post-pacing interval was determined during sustained ventricular tachycardia and, following its spontaneous termination during an episode when ectopic activity could only be induced by pacing. During sustained ventricular tachycardia there was a direct linear relation between the interstimulus interval of regular pacing and the first post-pacing interval. During the episode when ectopic activity could only be induced by pacing, shortening of the post-pacing interval resulted in biphasic behavior of the first post-pacing interval. Pacing with interstimulus intervals of more than 400 ms induced a first post-pacing interval equal to the interstimulus interval, whereas shorter interstimulus intervals induced a first post-pacing interval twice the interstimulus interval. When during regular pacing only the last pacing interval was changed, a similar biphasic response resulted. When toxicity had almost subsided, ectopic activity could only be induced following short pacing intervals (200-320 ms). Again, a direct linear relation was found between the pacing interval and the first post-pacing interval. Our findings strongly suggest that at different levels of digitalis intoxication triggered activity is the underlying mechanism for the first post-pacing QRS complex.

Animals↗

PubMed1986

Effects of different modes of stimulation on the morphology of the first QRS complex following pacing during digitalis-induced ventricular tachycardia: observations in the conscious dog with chronic complete atrioventricular block.

During digitalis-induced, sustained, monomorphic ventricular tachycardia, programmed electrical stimulation was performed and the effect on the first post-pacing QRS morphology was determined. Ventricular tachycardia was induced in nine conscious dogs with chronic complete atrioventricular block by administering digoxin i.v. 0.1 mg/kg given in 1-1 1/2 hour. Spontaneous ventricular tachycardia most frequently had a right bundle branch block morphology and an extreme left axis suggesting an origin in the apex of the left ventricle. Less frequently, a left bundle branch block-like configuration with an intermediate axis was observed, compatible with an origin in the basal part of the right ventricle. Following pacing close to one of these predilection sites, the first post-pacing QRS morphology suggested an origin close to the site of stimulation. Pacing distant from these predilection sites resulted in fusion complexes between electrical activation from these predilection sites and the stimulation site. The amount of fusion depended on interstimulus interval and the number of stimuli. Long interstimulus intervals and few stimuli induced a QRS complex similar to that of the spontaneous tachycardia. The faster and longer the stimulation train, the more the QRS complex became similar to the paced QRS complex. Similar findings were also observed on decreasing the last paced interval only. Our findings suggest that triggered activity is the underlying mechanism for the first post-pacing QRS complex. QRS configuration and the relation between the R-R interval and QRS configuration during tachycardia suggest that triggered activity is also the mechanism for the spontaneously occurring ventricular tachycardia during digitalis intoxication. These observations may have important clinical implications.

Animals↗

PubMed1983

Extrastimulus-related shortening of the first postpacing interval in digitalis-induced ventricular tachycardia: observations during programmed electrical stimulation in the conscious dog.

The effect of different modes of pacing on interval and configuration of the first postpacing QRS complex was studied during digitalis-induced ventricular tachycardia in the conscious dog. The effect of overdrive pacing was related to pacing rate; the longest pacing intervals resulted in prolongation of the first postpacing interval, while increasing the rate of overdrive pacing led to a progressive shortening of the first postpacing interval. When extrastimuli were introduced during fixed rate pacing, the duration of the first postpacing interval was found to be predominantly effected by the extrastimulus coupling interval. The importance of the last paced interval to the duration of the first postpacing cycle length was also observed when only a single or two extrastimuli were given. The duration of the first postpacing interval was found to be independent of the site site of stimulation. In contrast, the configuration of the first postpacing QRS complex was found to be related to the site of pacing; the first postpacing QRS complex originated close to the site of stimulation independent of the configuration of the tachycardia. In conclusion, it was found that during digitalis-induced ventricular tachycardia 1) the first postpacing interval is mainly, dependent on the interval of the last paced beat, 2) the length of the first postpacing interval is independent of the site of stimulation, but 3) the configuration of the first postpacing QRS complex is related to the site of stimulation. These findings may facilitate the understanding of complex ventricular arrhythmias observed during severe digitalis intoxication in human beings.

Animals↗