title: The relationship between overdrive suppression and overdrive excitation in ventricular pacemakers in dogs.
abstract: We studied the excitatory and inhibitory effects of overdrive on idioventricular pacemakers in anesthetized dogs with recently induced complete atrioventricular block. The following results were obtained: (1) a slow driving rate may induce a temporary rhythm which may be reinstituted with additional stimuli; (2) the induced rhythm may appear as coupled extrasystoles which, on interruption of the drive, are found to be self-sustaining; (3) during continued slow driving, extrasystoles may appear and disappear in a cyclical manner; (4) a short period of fast driving may be followed by a fast new rhythm, the rate and duration of which are a function of the rate and duration of drive; (5) fast driving may induce a new rhythm at a rate below predrive control; (6) after a long period fast driving, only suppression follows; and (7) intermittent periods of fast driving lead to a summation of inhibition with each successive period. These results suggest the following conclusions: (1) under certain conditions, electrical driving instead of inducing suppression may induce a rhythm ("overdrive excitation") at a rate similar to, faster then, or slower ("inhibited excitation") than control; (2) the duration of diastole and the number of driven beats are major factors in the induction of new rhythms; and (3) overdrive excitation is counteracted by overdrive inhibition, with development of the former requiring fewer beats than the latter.
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D006327:Heart Block / Q000503:physiopathology / Q000628:therapy*; D006329:Heart Conduction System / Q000503:physiopathology; D006339:Heart Rate; D006352:Heart Ventricles / Q000503:physiopathology; D008297:Male; D009200:Myocardial Contraction; D010138:Pacemaker, Artificial / Q000009:adverse effects