<Originals>β-adrenergic interaction in ST-segment and T wave elevation in myocardial infarct dogs

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Background : The exact mechanism behind exercise induced ST-segment elevation and T wave normalization in old myocardial infarction is still unknown. We had hypothesized that these ST-T changes were concerned with sympathetic nerve β action of the non-infarct region. To clarify this problem, an experimental study on both infarct and normal dogs was conducted. Methods : (1) Infarct dogs : Anterior wall infarction was prepared by cellulose embolization in 14 adult mongrel dogs. After seven days, 0.5ml of saline and 0.5ml of 0.5μg/ml isoproterenol (ISO) were infused into the left circumflex artery. In seven dogs, ISO was again injected following pretreatment with 0.1mg/kg of propranolol, and in the other seven dogs, following treatment with 0.1mg/kg of ouabain. (2) Normal dogs : In 7 thoracotomized dogs, ECG electrodes were fixed on the epicardial surface of the anterior and lateral wall. A bipolar aspiration electrode was situated for measuring monophasic action potential in the region of the left anterior descending artery. Drugs were infused ; 0.5ml of saline, 0.5ml of 0.5μg/ml ISO, 0.1ml/kg propranolol pretreatment, and 0.5ml of 0.5μg/ml ISO. Results : (1) In the infarct dogs, ST-segment in the infarct region significantly lowered 3 seconds after infusion of ISO and significantly elevated after 15 seconds, showing two phase changes. These changes were suppressed by the pretreatment of propranolol and ouabain. Myocardial lactate extraction ratio did not fall to less than 10% in each loading. (2) In normal dogs, ST-segment in the infusion region of ISO tended to fall 3 to 7 seconds after infusion, to elevate in 15 to 25 seconds and fell again after 40 seconds. These changes were suppressed by pretreatment with propranolol. In the non-injection region, slight opposite changes were observed but were not significant. T wave significantly decreased in the region of ISO injection 3 seconds after injection and significantly elevated after 15 seconds, showing two phase changes. In the non-injection region, a tendency of reverse changes was observed. Pretreatment with propranolol suppressed these changes. Conclusion : Sympathetic nerve β receptor activation in normal myocardium adjacent to infarcted myocardium markedly contributes to the elevation in ST-segment and T wave.
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<Originals>β-adrenergic interaction in ST-segment and T wave elevation in myocardial infarct dogs

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