Factors related to vulnerability to arrhythmias in acute myocardial infarction

Ion-selective electrodes designed in our laboratory have been employed to determine the characteristics of the changes in extracellular K+ and pH associated with acute coronary artery ligation and release. These studies have defined major inhomogeneities in the rate and magnitude of change of extracellular K+ and pH not only at the lateral margin of the ischemic zone but also between the subepicardium and subendocardium, between the subendocardium and endocardium, and even between closely spaced electrodes throughout the ischemic zone. The inhomogeneities during reperfusion were as great as or greater than those induced by coronary ligation. We have used papillary muscles of guinea pigs to determine the effect of the various combinations of extracellular pH and K+ observed at any point in time in an intact heart to study the anticipated changes in conduction and have found both a speeding and a slowing of conduction, which can be expected to occur simultaneously in an intact heart. These results indicate that significant inhomogeneities exist in the ionic and electrical consequences of acute coronary artery ligation and release and that these inhomogeneities can be expected to result in disorders of conduction leading to reentry.