Acute Myocardial Infarction And Characteristic ECG Changes

Acute myocardial infarction (AMI) presents distinct electrocardiogram (ECG) patterns that are crucial for timely diagnosis. In cases of Q-wave myocardial infarction, the ECG typically shows specific changes in the leads facing the area of transmural myocardial necrosis. These changes include a wide and deep Q wave, ST-segment elevation with a convex upward morphology, and deeply inverted, symmetric T waves.

ECG Patterns In Q-Wave Myocardial Infarction

These hallmark ECG findings are most evident in the leads that are positioned over the affected region of the heart. The presence of a pathologic Q wave — defined as a duration of more than 0.04 seconds and at least one-third the height of the R wave — is a key indicator of transmural damage.

Changes In Leads Opposite The Infarct Zone

Conversely, in the leads positioned away from the infarcted area, reciprocal changes may appear. These include an increased R wave amplitude, ST-segment depression, and tall, upright T waves. These opposing patterns help clinicians localize the site of myocardial injury.

Non-Q Wave Myocardial Infarction Features

In non-Q wave myocardial infarction, particularly in cases involving the subendocardial layer, the ECG may not display pathological Q waves. Instead, there is often ST-segment depression of ≥0.1 mV. Notably, in some instances, ST-segment elevation may be observed in lead aVR, along with symmetric T wave inversion.

Dynamic Nature Of ECG Changes

One of the most important aspects of ECG interpretation in AMI is its dynamic evolution over time. Serial ECGs are often necessary to capture the progression of ST-segment changes and T wave inversions, which supports the diagnosis of acute ischemia.

Localization Of Myocardial Infarction

The location and extent of a Q-wave myocardial infarction can be estimated by analyzing the number and position of leads showing characteristic changes. For example, anterior infarcts typically affect the precordial leads (V1–V4), while inferior infarcts involve leads II, III, and aVF.