Comparison of Clinical Significance of Programmed Stimulation Induced Ventricular Tachycardia and Fibrillation in Survivors of Acute Myocardial Infarction

Summary

The clinical significance of ventricular tachycardia and ventricular fibrillation induced at electrophysiology studies was examined in 64 patients (pts) studied after transmural acute myocardial infarction. Ten patients had had documented late ventricular arrhythmias prior to the electrophysiology study. The stimulation protocol included 2 extrastimuli (S₁S₂, S₂S₃) delivered after a paced rhythm at 2 right ventricular sites (apex, outflow tract) and at 2 current intensities (2x threshold, 20 mA). Patients were followed for 6–18 months after the study.

Of the fiftyfour patients with no documented ventricular arrhythmia, 23 were induced into fibrillation (group I), and 31 into tachycardia (group 2). All patients with documented ventricular arrhythmias were induced into tachycardia (group 3). There was no difference in patient age or infarct site amongst the three groups. Apart from two patients with an infarct age of greater than I year, infarcts to study time was greater than 1.5 weeks and less than 3 months S₁S₂ was not significantly different among the groups but S₂S₃ was significantly longer (242 msec ± 33) in group 3 than groups I and 2 (200 msec ± 40, 206 msec ± 41), p < 0.05. Minimum pacing amplitude to induce an arrhythmia was significantly lower in group 3 (10% at 20 mA) than in groups I and 2 (65% and 55%). None of the patients in group I died of cardiac causes while 27% of the patients in group 2 died of cardiac cause. The mean rate of the induced VT from the pts who died was slower, 244 ± 45 ppm than that of the VT in pts still alive 281 ± 44 ppm (p < 0.05). Fifty per cent of the patients in group 3 died of a cardiac cause.

The results indicate that after acute myocardial infarction (1) induced slow rate VT during an electrophysiology study is associated with a poorer prognosis than VF and fast VT; (2) induced VF may be of limited clinical significance. (3) VT is inducible with less aggressive stimulation in pts with documented ventricular arrhythmias.