Ventricular ectopic beats with fixed and variable coupling: Incidence, clinical significance and factors influencing the coupling interval☆

Abstract An analysis of possible factors which determine the coupling intervals of ventricular ectopic beats was made in the electrocardiograms of 88 persons who had at least 10 unifocal ventricular ectopic beats. The material was selected at random and included life insurance applicants, outpatients and patients from a psychiatric state hospital and a general hospital. The coupling interval which varied by less than 0.12 sec. was considered as fixed. Forty persons had fixed coupling and 48 variable coupling. Persons with no heart disease and three groups of patients with heart disease of varying severity had a similar incidence of fixed and variable coupling. Measurements of the relation between the duration of the coupling interval and the preceding R-R interval and of the duration of the interectopic intervals allowed us to separate the ventricular ectopic beat with variable coupling interval into several categories. However, we found no feature of ventricular ectopic beats which differentiated persons without heart disease from those with heart disease. Similarly we found no features of ventricular ectopic beats which differentiated persons receiving digitalis from those not receiving the drug. A significant positive or negative correlation between the duration of the preceding R-R interval and coupling interval was rarely found. In the great majority of the persons there was no significant correlation between the two parameters. Possible reasons for such distribution of correlations are discussed. An analysis of the timing of the ventricular ectopic beat during the cardiac cycle frequently revealed a “clear zone” free of ventricular ectopic beats between the end of the U wave and the onset of the P wave. This period of an apparent relative refractoriness of the ventricular myocardium was observed in persons with and without heart disease. Our results suggest that the factors which determine the time of appearance of ventricular ectopic beats with relation to the preceding R-R interval operate in the same manner regardless of the presence or absence of heart disease and treatment with digitalis.