Heart Attack ECG Characteristics

When a heart attack occurs, the heart muscle undergoes a process of injury and necrosis. Over time, the electrocardiogram (ECG) exhibits specific changes that can be categorized into several stages: the hyperacute phase, acute phase, subacute phase, and healing phase. In the hyperacute phase, tall T waves appear on the ECG, accompanied by upsloping or convex ST-segment elevation.

Acute Phase of Heart Attack

Several hours after the onset of a heart attack, the ST segment typically shows convex elevation. This elevation may form a prominent single upward curve before gradually decreasing. As the heart muscle undergoes necrosis, the R wave's amplitude diminishes and may even disappear. Abnormal Q waves begin to emerge, and T waves transition from upright to inverted, deepening over time. This stage often reveals pathological Q waves indicative of tissue death.

Subacute and Healing Phases

Subacute Phase

During the subacute phase, which occurs weeks after the heart attack, the elevated ST segment gradually returns to baseline levels. However, due to ongoing ischemia, inverted T waves may begin to normalize slightly. Importantly, the pathological Q waves remain present during this stage.

Healing Phase

In the healing phase, which develops several months after the heart attack, both the ST segment and T wave continue to normalize. However, in many cases, T waves remain inverted or flattened. The pathological Q waves, representing areas of myocardial scarring, typically persist indefinitely and serve as a long-term marker of prior heart damage.