Observations on the mechanism of human ventricular vulnerability during premature stimulation

Abstract

Sum_marySpontaneous ventricular extrasystoles (V3-beats) occur frequently after premature ventricular stimuli induced during a paced ventricular rhythm. The V3 phenomenon was observed in, 100 of 158 patients (63.3%) with and without heart disease being studied for the evaluation of various rhythm disorders. In patients with an old myocardial infarction there was an increased tendency to exhibit short ventricular salvos (V3-V 5 beats) after prematurely elicited test pulses. V~-beats occurred less frequently in patients with a bundle branch block than in patients with normal intraventricular conduction.The statistical analysis of several variables obtained during the investigation revealed that the frequency and the appearance time of the V 3 beats and the vulnerable period of the cardiac cycle are related to a critical delay of the retrograde Purkinje-His conduction time of the premature test pulse, the basic rate of the drive rhythm and the state of excitability of the ventricular myocardium. The results strongly suggest a re-entry mechanism generating the spontaneous ventricular extrasystoles. The main delay of conduction of the premature test pulse seems to be localized not within the working myocardial fibers or the proximal His-Purkinje system but rather within the distal Purkinje fiber system. Therefore, the re-entry pathway of the V~ beats is thought to be confined to the right ventricular Purkinje fiber network near the site of stimulation.Clinically, it can be deduced that an artificially induced ventricular re-entry beat is tolerated and extinguished in the stable heart by physiological protective mechanisms. In the diseased heart, however, an increased state of fiber inhomogenity may be generated by the V 3 beat leading to recurrent re-entry impulses.Premature right ventricular stimulation during a paced ventricular rhythm has become a routine procedure in clinical electrophysiology. Early test pulses may lead to spontaneous ventricular extrasystoles. These beats have to be considered as a variant form of human ventricular vulnerability. Usually, only one spontaneous ventricular extrasystole *) Supported by Deutsche Forschungsgemeinschaft SFB 109 807

Vulnerability of the right ventricle to cathodal, anodal, and bipolar stimulation at double diastolic threshold strength

“…-Repetitive ventricular response (RVR) defines the occurrence of one or more nonstimulatr ventricular beats in response to the test stimulus or stimuli, providing that no His potential precedec these beats or with a HV-interval less than that observed during sinus rhythm. The repetitive ventricular response was differentiated from the so-called intra-His-reentry or V phenomenon (2,5,6). This type of reentry is dependent upon a critical degree of retrograde Hi Purkinje conduction delay (V-H prolongation) (2).…”

“…During electrophysiologic investigations in humans, a bipolar stimulation technique is used with a much lower current intensity (about twice threshold current) than in pacemaker patients. Nevertheless, repetitive ventricular response -as a sign of increased ventricular vulnerability -can occasionally be induced (5,6,8,13).…”