Systolic and diastolic pacemaker induced repetitive firing in the human heart. Analysis of 23 cases

Twenty-three tracings obtained from patients showing pacemaker-induced repetitive firing were reviewed. This complication was manifested as single extra beats, ventricular tachycardia and ventricular fibrillation. Cases in which a definite relation between pacemaker stimuli and multiple responses could not be established were excluded from this series. Systolic repetition was observed in 17 patients. This phenomenon, which was attributed to ventricular vulnerability occurred during chronic block (12 cases) as well as during acute myocardial infarction (5 cases). There were 5 instances of diastolic repetitive firing in patients with digitalis intoxication and recent myocardial infarction. It was postulated that a Wedensky-effect best explained the genesis of diastolic repetition. Knowledge regarding the types and possible mechanisms of the different types of repetitive firing can be applied for the safer use of continuous, demand and ventriculo-synchronized pacemakers.