Heart Attack ECG Patterns: What You Need To Know

Heart attacks, or myocardial infarctions, can be identified through specific electrocardiogram (ECG) patterns. These patterns vary depending on the stage of the heart attack and the affected area of the heart. Understanding these ECG characteristics is crucial for timely diagnosis and effective treatment. Here's a detailed breakdown of what ECG readings typically show during a heart attack.

1. Hyperacute Phase of Acute Myocardial Infarction

In the very early stages of a heart attack—within minutes of symptom onset—the ECG may show subtle but significant changes. Initially, there is a brief period of subendocardial ischemia, which manifests as tall, peaked T waves. This is quickly followed by ST-segment elevation, either in an upsloping or convex (upward-curving) pattern. This ST elevation often merges with the tall T waves, creating a distinctive appearance. Prompt medical intervention during this phase can prevent full-blown myocardial infarction or reduce the extent of heart muscle damage.

2. Acute Phase of Myocardial Infarction

Within hours to days after the onset of a heart attack, the ECG undergoes dynamic changes. The ST segment remains elevated, often forming a single, continuous curve known as a monophasic configuration. Over time, this elevation gradually diminishes. As heart muscle cells die, the ECG begins to show signs of necrosis. Specifically, the R wave amplitude decreases or disappears in leads facing the damaged area, leading to the appearance of abnormal Q waves or QS complexes. Meanwhile, T waves transition from upright to inverted, deepening over time to form what is known as a "coronary T wave." During this phase, all three classic ECG signs—abnormal Q waves (necrosis), ST-segment elevation (injury), and T-wave inversion (ischemia)—can be present simultaneously.

Key ECG Features in the Acute Phase:

• ST-segment elevation: Prominent and often convex upward.
• Q waves: Begin to appear as heart tissue dies.
• T-wave inversion: Progresses from upright to deeply inverted.

3. Subacute Phase of Myocardial Infarction

Weeks to months after the heart attack, the ECG pattern stabilizes. The ST-segment elevation resolves and returns to baseline levels. The T-wave inversion, which was previously deep, starts to normalize but may remain inverted for some time. Importantly, the Q waves caused by myocardial necrosis typically persist indefinitely and serve as a permanent marker of prior heart damage. This phase is characterized primarily by signs of healed or healing injury, with the ECG reflecting the long-term consequences of the event.

Clinical Significance of ECG Monitoring

Monitoring ECG changes throughout the phases of a heart attack is essential for assessing the progression and severity of myocardial damage. These evolving patterns help clinicians determine the timing of the infarction, the effectiveness of treatment, and the need for further interventions such as angioplasty or bypass surgery. Early recognition of ECG abnormalities significantly improves patient outcomes.