Mechanism and Time Course of S-T and T-Q Segment Changes during Acute Regional Myocardial Ischemia in the Pig Heart Determined by Extracellular and Intracellular Recordings

• Published in: Circulation research 1978-05, Vol.42 (5), p.603-613
• Main Authors: KLEBER, ANDRE G, JANSE, MICHIEL J, VAN CAPELLE, FRANS J.L, DURRER, DIRK
• Format: Article
• Language: English
• Subjects: Action Potentials; Animals; Coronary Disease - physiopathology; Electrocardiography; Heart - physiopathology; In Vitro Techniques; Membrane Potentials; Swine
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.42.5.603

We recorded transmembrane potentials from subepicardial ventricular cells and local extracellular DC electrograms in isolated perfused pig hearts before and after occlusion of the left anterior descending artery. The first change was a decrease in the resting membrane potential, reflected by T-Q depression in the electrogram. After 3 minutes, action potentials shortened and their amplitude decreased, resulting in S-T elevation until, finally, cells in the center of the ischemic zone became totally unresponsive at resting potentials of about −65 mV. This rendered the extracellular complex monophasic. Determination of extracellular potential distribution at 150-250 epicardial sites after 15-30 minutes of occlusion showed an increase of T-Q depression and S-T elevation toward a central area, with maximum values of −15 and +35 mV, respectively. Comparison of amplitude and configuration of intramural and epicardial potential profiles revealed that the potential distribution was homogeneous throughout ischemic parts of the wall. Extracellular epicardial current originated, therefore, from the epicardial intracellular compartment. Maximal current density during late systole was 1 μA/mm , flowing in the border zone towards normal myocardium. After 1 hour of occlusion, there was a marked decrease of extracellular DC potentials which could be attributed to transient recovery of electrical activity in the ischemic zone. After 2 hours, the zone of unresponsiveness was larger than after 15 minutes of occlusion, and the overall amplitude of DC potentials had decreased further, possibly because of healing over.