[Isoproterenol induces ST-segment elevation without wall motion aggravation and myocardial ischemia in experimental myocardial infarction].

The mechanism of exercise-induced ST-segment elevation in previous myocardial infarction was investigated using isoproterenol infusion with atrial pacing to simulate exercise hemodynamics in seven closed chest dogs with myocardial infarction. The myocardial infarction was induced by cellulose embolization of the left anterior descending artery. One week after infarction, 1) isoproterenol 0.3 microgram/min infusion, 2) right atrial pacing alone, and 3) isoproterenol infusion after the injection of propranolol 0.5 mg/kg were performed. The heart rate was kept constant by atrial pacing during the examination. Precordial ST-segment deviation, left ventricular global and regional wall motions, lactate extraction ratio, and regional myocardial blood flow were measured. Isoproterenol induced a significant elevation of the ST-segment, i.e., the sum of ST-segment elevation at chest leads V2, V3 and V4, sigma STV234, increased from 0.32 +/- 0.11 (mean +/- SEM) to 0.82 +/- 0.22 mV (p < 0.01). However, pacing alone and isoproterenol with pretreated propranolol did not. During isoproterenol-induced ST-segment elevation, left ventricular ejection fraction increased (29.2 +/- 3.3 to 39.1 +/- 3.9%, p < 0.01), lactate extraction ratio decreased but within the normal range for lactate metabolism (30.2 +/- 7.0 to 16.7 +/- 4.2%, p < 0.01), and the inner/outer ratio of regional blood flow did not change significantly (0.81 +/- 0.18 to 0.97 +/- 0.13 in the non-infarct border area, NS; 0.37 +/- 0.04 to 0.42 +/- 0.07 in the infarct border area, NS). Isoproterenol enhanced ventricular wall motion in the border and non-infarct areas, but did not induce aggravation in the infarct area.(ABSTRACT TRUNCATED AT 250 WORDS)