ST-segment, T-wave, and U-wave changes during myocardial ischemia and after myocardial infarction
Insights
This review explains how myocardial ischemia causes ventricular repolarization abnormalities, focusing on ST segment deviations and T wave changes. Understanding these ECG patterns is crucial for diagnosing heart attacks and related conditions.
Area of Science:
- Cardiology
- Electrophysiology
- Pathophysiology
Background:
- Myocardial ischemia frequently causes ventricular repolarization abnormalities.
- ST segment deviation is a common sign of acute myocardial ischemia due to injury currents.
- Transient T wave and QT interval changes occur, followed by persistent abnormalities.
Purpose of the Study:
- To review the pathogenesis of ischemia-related ventricular repolarization abnormalities.
- To discuss the patterns and mechanisms of ST deviations, T wave changes, and QT interval alterations during and after myocardial infarction.
- To explore less common ischemic manifestations like ST alternans, T alternans, and negative U waves.
Main Methods:
- Review of existing literature on myocardial ischemia and electrocardiographic changes.
- Analysis of the mechanisms underlying ST segment and T wave abnormalities.
- Discussion of differential diagnoses and diagnostic tools, including isoproterenol challenge.
Main Results:
- ST segment deviation (elevation or depression) is a primary indicator of acute ischemia.
- Transient T wave and QT changes evolve into persistent abnormalities, linked to action potential duration changes.
- Persistent ST elevation post-myocardial infarction may indicate ventricular dyskinesia.
Conclusions:
- Electrocardiographic changes, particularly ST and T wave abnormalities, are key indicators of myocardial ischemia.
- Understanding the evolution and specific patterns of these changes aids in diagnosis and prognosis.
- Isoproterenol administration can help differentiate ischemic T wave changes from functional or neurogenic ones.
Abstract:
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.
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