Elevated sympathetic response of epicardium proximal to healed myocardial infarction

Sympathetic nerve interaction with cardiac electrophysiology was evaluated in healed myocardial infarction by monitoring the effects of sympathetic nerve stimulation on local epicardial refractoriness in cats. Single-stage distal coronary artery ligation was used to induce myocardial infarction. Regions overlying and surrounding infarcts 3 mo after healing and comparable regions in sham-operated and normal unoperated hearts were studied. Local ventricular muscle refractory periods were measured by the extrastimulus technique from 1) the epicardium overlying the infarct, 2) the area bordering the infarct, and 3) a normal area proximal to the infarct on the anterior free wall of the left ventricle. Bilateral stimulation of the ansa subclavia induced significant and disparate refractory period shortening (P less than or equal to 0.01) in hearts with healed myocardial infarction. Shortening was greatest in the normal area [-26 +/- 8 (+/-SD) ms], less in the border area (-15 +/- 6), and least in the infarct area (-7 +/- 2). In contrast, refractory periods measured in noninfarcted hearts shortened significantly (P less than or equal to 0.01) but uniformly and to a lesser extent during sympathetic stimulation. We conclude 1) the effects of sympathetic nerve stimulation are more pronounced in the areas proximal to healed infarction than in similar areas of noninfarcted hearts and 2) a marked disparity in sympathetic responsiveness occurs in hearts with healed myocardial infarction.