From the Guidelines
During a myocardial infarction, characteristic ECG changes include ST segment elevation, T wave inversion, and the development of pathological Q waves, as outlined in the third universal definition of myocardial infarction 1. These changes are crucial for diagnosing and managing MI, as they can indicate the location and extent of myocardial damage.
- The earliest change is often ST segment elevation in the leads corresponding to the affected area of the heart, which can be accompanied by reciprocal ST depression in opposing leads.
- As the infarction progresses, T wave inversion may occur, followed by the development of pathological Q waves, indicating permanent myocardial damage.
- Hyperacute T waves, which are tall and peaked, may be seen before ST elevation becomes apparent, particularly in the acute phase of an MI 1.
- The specific pattern of ECG changes can vary depending on the location of the infarct, such as anterior, inferior, or lateral, and the time elapsed since the onset of symptoms.
- Continuous ECG monitoring is essential in the acute setting to track these dynamic changes and guide treatment decisions, with serial recordings recommended at 15-30 minute intervals if the initial ECG is non-diagnostic 1.
From the Research
ECG Changes During Myocardial Infarction
The electrocardiogram (ECG) is a crucial tool for diagnosing myocardial infarction (MI) and monitoring its progression. Several studies have investigated the ECG changes that occur during MI, including:
- Increase in ST-segment deviation (30%) and ST-segment normalization (70%) during reperfusion of the infarct-related coronary artery 2
- Terminal T-wave inversion (60%) and accelerated idioventricular rhythm (51%) are also common ECG changes during reperfusion 2
- Nonsustained ventricular tachycardia (7%) and bradycardia (18%) may also occur during reperfusion 2
Classic ECG Descriptions
Classic electrocardiographic descriptions of MI include Q wave and non-Q wave infarction, as well as ST segment and T wave infarction 3. The electrophysiology of these ECG changes is related to the depolarization and repolarization of the heart muscle during ischemia and infarction 4.
Advanced ECG Techniques
Advanced ECG techniques, such as body surface potential mappings (BSPMs) and spatiotemporal inverse ECG (ST-iECG) modeling, can provide more detailed information about the location and extent of MI 5. These techniques can reconstruct heart-surface electrograms and identify negative QRS waves, which may indicate potential regions of MI 5.
ST-Segment Changes
ST-segment changes are a key component of ECG diagnosis during acute myocardial ischemia 6. The 12-lead ECG can detect ST-segment changes associated with ischemia, but alternative electrocardiographic leads may be optimized for detection of ischemia originating in different regions of the ventricular myocardium 6.