Which of the following is the earliest sign of acute transmural infarction?

• A. ST segment depression
• B. T wave inversion
• C. ST segment elevation
• D. Prolonged QT interval

Answer: (C)

Acute transmural infarction is characterized by damage to the heart muscle due to a cessation of blood flow, often caused by coronary artery occlusion. The earliest and most significant electrocardiographic change associated with this condition is ST segment elevation. This is a direct result of the ischaemia affecting the myocardium, which leads to alterations in the cardiac action potentials.

In the early stages of acute transmural infarction, the injured myocardial cells become more depolarized than normal, resulting in a change that manifests as an elevation of the ST segment on the ECG. This elevation is indicative of the acute phase of the infarction and typically occurs within minutes to hours after the onset of ischaemia.

Other changes, such as T wave inversion and ST segment depression, may also occur with myocardial ischaemia but are typically seen later or in the context of different types of myocardial injury, such as unstable angina or nontransmural infarction. Prolonged QT interval can occur due to various factors but is not a direct indication of acute transmural infarction.

Thus, ST segment elevation is the key and earliest sign of acute transmural infarction, making it the correct answer to the question.