Acute ischemic ventricular arrhythmias in pigs with healed myocardial infarction: comparative effects of ischemia at a distance and ischemia at the infarct zone.

BACKGROUND

The myocardium bordering a healed infarction undergoes electrophysiological and autonomic neural derangements that may interact with a new ischemic episode to promote arrhythmias. Therefore, peri-infarction ischemia may be more arrhythmogenic than ischemia at a distance from the infarct zone, but this is not known.

METHODS AND RESULTS

Forty-two anesthetized open-chest pigs with a 1-month-old myocardial infarction induced by permanent ligature of the distal left anterior descending coronary artery (LAD) underwent a coronary reocclusion at either the proximal LAD (group 1, peri-infarction ischemia, n=21) or at the circumflex coronary artery (group 2, ischemia at a distance, n=21). Ventricular arrhythmias were analyzed during 60 minutes of coronary reocclusion and during programmed electrical stimulation. Infarct size was measured, and underperfusion at the occluded area was estimated by recording 99mTc-tetrofosmin activity. Weights of acute ischemic (23+/-9 versus 21+/-9 g) and healed infarction (10+/-6 versus 10+/-3 g), baseline LV pressure and peak of LV dP/dt, and radiotracer activity at the occluded area (3+/-2% versus 5+/-2% of normal tissue) were comparable between the two groups. Compared with group 2, group 1 showed more ventricular premature beats (median, 136 versus 59; P=.008), a higher incidence of spontaneous sustained ventricular tachycardia (57% versus 19%, P=.02) and ventricular fibrillation (76% versus 47%, P=.05), and greater electrical inducibility of sustained ventricular tachycardia (65% versus 28%, P=.03) but comparable induction of ventricular fibrillation.

CONCLUSIONS

Ischemia superimposed at the border of a 1-month-old myocardial infarction is more arrhythmogenic than ischemia at a distance from the infarct zone in swine. Data suggest the presence of electrophysiological instability at the peri-infarction zone.