Why does the ST segment elevate during myocardial ischemia?

From the Guidelines

ST segment elevation during ischemia occurs because of electrical current differences between injured and healthy heart tissue, creating a voltage gradient that appears as elevation of the ST segment on an ECG. This phenomenon is a result of the affected cells being unable to maintain normal electrical properties due to reduced blood flow, leading to a state of partial depolarization at rest 1. The injured cells remain partially depolarized, causing current to flow from the damaged area to the healthy tissue, which is most pronounced in ECG leads that face the area of injury.

The degree of ST elevation often correlates with the severity of ischemia, with more pronounced elevation suggesting more extensive damage, as outlined in the 2017 ESC guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation 1. According to these guidelines, ST-segment elevation is considered suggestive of ongoing coronary artery acute occlusion in cases where there is at least two contiguous leads with ST-segment elevation of a certain magnitude, depending on the lead and patient demographics.

Key points to consider when interpreting ST segment elevation include:

• The magnitude of ST elevation, with higher elevations indicating more severe ischemia
• The location of ST elevation, with different leads corresponding to different areas of the heart
• The presence of other ECG changes, such as T wave inversion or Q wave development, which can indicate the progression of ischemia to infarction
• The clinical context, including patient symptoms and medical history, which can inform the interpretation of ECG findings and guide further management, as recommended by the ESC guidelines 1.

From the Research

ST Segment Elevation During Ischemia

• The ST segment elevation during ischemia is a critical indicator of acute myocardial infarction, particularly ST-segment elevation myocardial infarction (STEMI) 2, 3, 4, 5, 6.
• STEMI is caused by a complete coronary artery occlusion, which leads to a sudden reduction in blood supply to the heart 3, 6.
• The elevation of the ST segment is a result of the ischemic damage to the heart muscle, which alters the electrical activity of the heart 6.
• The diagnosis of STEMI is typically made using electrocardiography (ECG), which shows persistent ST-segment elevation or presumably new left bundle branch block 3, 4.
• The treatment of STEMI involves rapid reperfusion therapy, either through primary percutaneous coronary intervention (PCI) or fibrinolysis, to restore blood flow to the affected area of the heart 2, 3, 4, 5, 6.

Pathophysiology of STEMI

• The pathophysiology of STEMI involves the formation of a thrombotic occlusion in an epicardial coronary vessel, which develops from an atherosclerotic plaque 6.
• The complete occlusion of the coronary artery leads to a sudden reduction in blood supply to the heart, resulting in ischemic damage to the heart muscle 3, 6.
• The ischemic damage alters the electrical activity of the heart, leading to the elevation of the ST segment on the ECG 6.

Treatment and Management

• The treatment of STEMI involves rapid reperfusion therapy, either through primary PCI or fibrinolysis, to restore blood flow to the affected area of the heart 2, 3, 4, 5, 6.
• Primary PCI is the preferred reperfusion strategy, but if it cannot be performed within 120 minutes of STEMI diagnosis, fibrinolysis therapy should be administered 3, 4, 6.
• The initiation of networks to provide around-the-clock cardiac catheterization availability and the generation of standard operating procedures within hospital systems have helped to reduce the time to reperfusion therapy 6.