ST-Segment Elevation in ECG: Acute Myocardial Infarction

The ST-segment is a portion of the electrocardiogram (ECG) that represents the early phase of ventricular repolarization. It is the interval between the end of the QRS complex and the beginning of the T wave. The ST-segment should normally be at the baseline or isoelectric line.

1. Acute Myocardial Infarction:
When there is an elevation of the ST-segment on an ECG, it is an important indication of acute myocardial infarction (AMI), commonly known as a heart attack. AMI is a condition characterized by a sudden blockage of blood flow to a part of the heart muscle, leading to tissue damage and potential death of heart cells.

The ST-segment elevation in AMI occurs due to the transmural ischemia, which means that the entire thickness of the heart muscle is affected by inadequate blood supply. Ischemia in the affected area leads to an imbalance between oxygen supply and demand, resulting in injury to the myocardium.

The ST-segment elevation is typically seen in specific leads that correspond to the area of the heart affected by the infarction. For example, if the ST-segment elevation is seen in leads V1 to V4, it suggests an anterior myocardial infarction involving the left anterior descending coronary artery.

The extent and magnitude of ST-segment elevation can provide valuable information about the severity of the infarction. In addition to ST-segment elevation, other ECG changes such as Q waves and T-wave inversion may also be observed in AMI.

2. Insufficient Supply of Oxygen to the Heart Muscles:
While the elevation of the ST-segment is predominantly associated with acute myocardial infarction, it can also occur in other conditions where there is insufficient supply of oxygen to the heart muscles. These conditions include:

- Unstable angina: Unstable angina refers to chest pain or discomfort that occurs at rest or with minimal exertion. It is caused by reduced blood flow to the heart, which can lead to ST-segment elevation on the ECG.

- Prinzmetal's angina: Prinzmetal's angina, also known as variant angina, is caused by coronary artery spasm. During a spasm, blood flow to the heart is temporarily blocked, resulting in ST-segment elevation.

- Coronary artery dissection: Coronary artery dissection is a tear in the inner layer of the coronary artery, leading to a separation of the layers and impaired blood flow. This condition can cause ST-segment elevation on the ECG.

- Myocarditis: Myocarditis is the inflammation of the heart muscle. It can result in ST-segment elevation, along with other ECG changes, depending on the severity and extent of the inflammation.

In summary, while the elevation of the ST-segment in an ECG can indicate conditions other than acute myocardial infarction, it is primarily associated with AMI. Prompt recognition of ST-segment elevation on an ECG is crucial for the early diagnosis and management of myocardial infarction, as it signifies an ongoing ischemic event that requires immediate medical intervention.