ST-segment, T-wave, and U-wave Changes During Myocardial Ischemia and After Myocardial Infarction

This review deals with the pathogenesis of ischemia-related abnormalities of ventricular repolarization. The most common repolarization abnormality during acute myocardial ischemia is the deviation of ST segment from the baseline due to diastolic and systolic currents of injury. The patterns of primary and reciprocal ST deviations during and after myocardial infarction are discussed. A very tall upright or a deeply inverted T wave, and shortened QT interval are transient phenomena followed by postischemic T wave abnormalities associated with QT lengthening. These changes are associated with lengthening of the ventricular action potentials at the border of infarction. Persistence of ST elevation after myocardial infarction is usually associated with ventricular dyskinesia. The differential diagnosis of this pattern and its possible mechanism are discussed. Also the mechanisms of ST alternans, T alternans and negative U waves, i.e. less common manifestations of myocardial ischemia are discussed. Studies of exercise-induced T wave normalization suggest that the behavior of primary T wave abnormalities after exercise does not alter the interpretation of the ischemic changes. T wave abnormalities are frequently non-specific but the post myocardial infarction T wave changes persist after administration of isoproterenol while various functional and neurogenic T wave abnormalities are corrected by isoproterenol.