Late induction of tachycardia in patients with ventricular fibrillation associated with acute myocardial infarction

A prospective study was made of 57 asymptomatic patients, 1 to 24 months after acute myocardial infarction, 17 with (Group I) and 40 without (Group II) ventricular fibrillation during the acute event. None of the 57 patients had symptomatic arrhythmias, uncontrolled heart failure or unstable angina. There was no significant difference between the two patient groups in time from acute myocardial infarction, medication used or left ventricular ejection fraction. Repetitive forms of arrhythmia (Lown grade 4) were more prevalent (29 versus 16%, not significant) during 24 hour ambulatory monitoring in patients in Group I (ventricular fibrillation group). Programmed extrastimulation was performed using 1 to 3 twice-threshold, 2 ms decremental extrastimuli delivered during right ventricular drive. Of the 17 patients in Group I, 8 had no induced arrhythmia (less than or equal to 4 extra responses), 4 had nonsustained ventricular tachycardia and 5 had sustained ventricular tachycardia (degenerating into ventricular fibrillation requiring electrical reversion in 4). None of the 40 patients in Group II had induced sustained ventricular tachycardia (p less than 0.005), although 9 had nonsustained ventricular tachycardia. Patients with ventricular fibrillation during acute myocardial infarction may have an increased risk for ventricular tachycardia or ventricular fibrillation that may be exposed by programmed electrical stimulation even when not yet clinically manifest.