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 elec trophysiological and autonomic neural derangements that may interact w ith a new ischemic episode to promote arrhythmias. Therefore, peri-inf arction ischemia may be more arrhythmogenic than ischemia at a distanc e from the infarct zone, but this is not known. Methods and Results Fo rty-two anesthetized open-chest pigs with a 1-month-old myocardial inf arction induced by permanent ligature of the distal left anterior desc ending coronary artery (LAD) underwent a coronary reocclusion at eithe r the proximal LAD (group 1, peri-infarction ischemia, n=21) or at the circumflex coronary artery (group 2, ischemia at a distance, n=21). V entricular arrhythmias were analyzed during 60 minutes of coronary reo cclusion and during programmed electrical stimulation. Infarct size wa s measured, and underperfusion at the occluded area was estimated by r ecording Tc-99m-tetrofosmin activity. Weights of acute ischemic (23+/- 9 versus 21+/-9 g) and healed infarction (10+/-6 Versus 10+/-3 g), bas eline LV pressure and peak of LV dP/dt, and radiotracer activity at th e occluded area (3+/-2% versus 5+/-2% of normal tissue) were comparabl e between the two groups. Compared with group 2, group 1 showed more v entricular premature beats (median, 136 versus 59; P=.008), a higher i ncidence 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 fibrill ation. Conclusions Ischemia superimposed at the border of a 1-month-ol d myocardial infarction is more arrhythmogenic than ischemia al a dist ance from the infarct zone in swine. Data suggest the presence of elec trophysiological instability at the peri-infarction zone.