Simultaneous recording of action potentials from endocardium and epicardium during ischemia in the isolated cat ventricle: relation of temporal electrophysiologic heterogeneities to arrhythmias.

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Abstract
We studied the effects of ischemia on transmembrane action potentials, conduction time, and refractory periods of both endocardial and epicardial muscle cells of coronary-perfused cat left ventricles. Oxygenated Tyrode's solution was perfused through the left anterior descending coronary artery, while the preparation was superfused with Tyrode's solution gassed with 95% N2 and 5% CO2. Transmembrane action potentials recorded simultaneously from endocardial and epicardial cells were normal during coronary perfusion. When perfusion was discontinued ("ischemia"), rapid deterioration of action potentials and prolongation of conduction time were observed in both endocardial and epicardial cells. The magnitude of the reduction of action potential amplitude and action potential duration (APD), and of prolongation of conduction time, was greater in epicardial cells than in endocardial cells, although the change in resting membrane potential was almost the same. However, APD of endocardial cells decreased progress...

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