Comparison of the Effects of Regional Ischemia and Hyperkalemia on the Membrane Action Potentials of the In Situ Pig Heart

APD During Ischemia. Introduction: This study was designed to determine the role of increased extracellular potassium [K + ] e on action potential duration (APD) in the in situ porcine heart during acute regional no‐flow ischemia. Methods and Results: In open chest, anesthetized swine, an arterial shunt from the carotid artery to the mid‐left anterior descending coronary artery was created through which a solution of KCl was infused to raise [K + ] e , Myocardial [K + ] e , was determined by potassium‐sensitive electrodes, and transmembrane action potential was recorded by floating glass microelectrode. During the first 2 minutes of ischemia, APD at 90% repolarization (APD 90 ) lengthened by 31.2 ± 1.1 msec (P < 0.05). The comparable increase in [K + ] e alone shortened APD 90 , During the next 6 minutes of ischemia. [K + ] e , rose to 11.3 ± 0.3 mM and APD 90 , showed a decrease. However, the comparable increase in |K + ] e , by infusion of KCl caused further shortening of APD 90 , at similar levels of [K + ] e . Conclusions: Acutely ischemic myocardium showed a brief increase in APD 90 , during the first 2 minutes of ischemia, followed by a fall in APD 90 , after 2 minutes of ischemia, but the shortening is less than anticipated by the rise in [K + ] e . Thus, we hypothesize that other component(s) of ischemia may inhibit action potential repolarization.