**Question:** In left sided massive pneumothorax, ECG shows all, except

A. S1Q3T3 pattern
B. S1 and S2 split
C. ST segment elevation
D. ST segment depression

**Correct Answer:** B. S1 and S2 split

**Core Concept:** In a left-sided massive pneumothorax, the ECG changes are due to the compression of the left heart chamber (left ventricle) and the mediastinal shift.

**Why the Correct Answer is Right:** When a massive pneumothorax occurs on the left side, it leads to a decrease in the size of the left ventricle, which in turn causes the S1 and S2 split in the ECG. The split indicates a decrease in the amplitude of S1 and S2 due to the reduced left ventricular size.

**Why Each Wrong Option is Incorrect:**

A. S1Q3T3 pattern: This pattern is typically seen in cardiac causes, such as myocardial infarction or left ventricular hypertrophy. It is not specific to pneumothorax and is not seen in the correct answer (S1 and S2 split).

B. ST segment elevation: ST segment elevation is seen in acute myocardial infarction (heart attack) and is not specific to pneumothorax.

C. ST segment depression: ST segment depression is seen in ischemia, infarction, or infarction risk factors, but not in pneumothorax, which leads to the correct ECG finding (S1 and S2 split).

D. The ST segment depression is a common finding in acute myocardial infarction (heart attack) and is not specific to pneumothorax.

**Clinical Pearl:** Massive pneumothorax can present with various ECG changes due to the compression of the heart and mediastinal shift. Understanding these changes is essential for the accurate diagnosis and management of pneumothorax.