Multiformity of induced unifocal ventricular premature beats in human subjects: Electrocardiographic and angiographic correlations.

Single ventricular premature responses induced by strength-interval pacing were elicited at multiple sites in 30 patients undergoing cardiac catheterlzation to determine if and under what circumstances unequivocally unifocal stimulated ventricular premature beats could manifest multiformity of the QRS configuration. Multiformity was defined as unifocal responses whose mean frontal axes differed by greater than 15 ° with or without associated morphologic differences in the horizontal leads. Multiformity occurred in 12 (40 percent) of 30 patients. A statistically significant association was found between multiformity and the presence of a quantitatively defined left ventricular wall motion abnormality (p < 0.01), prior myocardial infarction (p < 0.01) and a left ventricular ejection fraction of less than 0.60 (p < 0.05). Twelve (67 percent) of the 18 patients without multiformity had coronary artery disease, but only 4 of those 12 had a left ventricular wall motion abnormality or prior myocardial infarction, or both. Multiformity was also dependent on the site of stimulation and on the degree of prematurity. The results of this study indicate that the QRS configuration of early premature beats cannot be relied on as a predictor of their site of origin and multiformity is not necesarily synonymous with multifocality.