Frequency and significance of induced sustained ventricular tachycardia or fibrillation two weeks after acute myocardial infarction

Abstract

Electrophysiologic study, 24-hour ambulatory electrocardiographic monitoring, treadmill exercise test and angiographic evaluations were performed in 45 patients 14 ± 3 days (mean ± standard deviation) after acute myocardial infarction. Electrophysiologic study protocol included burst ventricular pacing and 1 to 3 ventricular extrastimuli at 2 cycle lengths from right ventricular apex, right ventricular outflow and left ventricle. Sustained monomorphic ventricular tachycardia (VT) (13 patients) or ventricular fibrillation (VF) (7 patients) was induced in 20 patients (44%) (group I). In these 20 patients, VT/VF was inducible with 2 extrastimuli in 10 patients, 3 extrastimuli in 9 patients and burst pacing in 1 patient. In the remaining 25 patients (56%), induction of no fewer than 7 ventricular beats were noted (group II). Severe left ventricular (LV) wall motion abnormalities occurred in 70% of group I patients and 22% of group II patients (p <0.005). There was no difference in the site of infarction, frequency and grade of ventricular ectopic rhythm on ambulatory electrocardiographic monitoring, double product on submaximal exercise, LV ejection fraction, and number of obstructed coronary arteries (70% or greater) (p >0.01) between group I and group II patients. During a mean follow-up of 10 ± 3 months, 1 patient in each group died suddenly, and in 1 group 1 patient spontaneous sustained VT developed which was identical in morphologic configuration to that induced during electrophysiologic study. In conclusion, electrical induction of sustained VT or VF during electrophysiologic study is common in patients 2 weeks after acute myocardial infarction. These patients have an increased incidence of LV wall motion abnormalities. The prognostic significance of this finding requires further follow-up study but appears to be of limited value.