Effects of various agents on regional ischemic myocardial injury: Electrocardiographic analysis

Abstract

Myocardial unipolar electrical potentials were recorded in 52 open-chest dogs from multiple epicardial and subendocardial sites in an area judged to be perfused by a small branch of the anterior descending coronary artery. The degree of individual electrode S-T segment shift was utilized as a measurement of the degree of localized myocardial ischemia. Individual electrode voltage shifts were summed (Σ) from the respective recording areas and expressed in millivolts as total epicardial and subendocardial Σ S-T segment elevation. Repeated five-minute occlusion challenges at 30 minute intervals resulted in reproducible degrees of Σ S-T segment shifts at both sites after the second occlusion challenge. Isoproterenol (0.25 and 1.0 μg per kilogram per minute) and norepinephrine (1.0 μg per kilogram per minute) infused intravenously increased the degree of the Σ S-T segment response during the ischemic chanllenge, as did increasing the heart rate an average of 42 beats per minute. Conversely, norepinephrine (0.1 μg per kilogram per minute) and propranolol (1 mg. per kilogram) reduced the degree of ischemic Σ S-T segment response. Consistent regional differences in either the direction or magnitude of the ischemic Σ S-T segment shifts were not observed during any of the above interventions. It is concluded that changes in the epicardial electrograms largely reflect the degree of subendocardial ischemia as determined electrocardiographically under the above experimental conditions.