Most common ECG change in pulmonary embolism is: September 2009
**Core Concept**
Pulmonary embolism (PE) is a life-threatening condition where a blood clot blocks the flow of blood in the lungs. In this scenario, the ECG (electrocardiogram) changes are a result of the body's compensatory mechanisms in response to the reduced blood flow to the lungs.
**Why the Correct Answer is Right**
The most common ECG change in pulmonary embolism is the S1Q3T3 pattern. This pattern is characterized by an S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. This occurs due to the acute right heart strain caused by the PE, leading to a right axis deviation and right bundle branch block. The S1Q3T3 pattern is a classic sign of pulmonary embolism, although it is not present in all cases.
**Why Each Wrong Option is Incorrect**
**Option A:** T wave inversion in V1-V3 is more commonly associated with myocardial ischemia, not pulmonary embolism.
**Option B:** Left bundle branch block is a sign of left ventricular hypertrophy or ischemia, not pulmonary embolism.
**Option C:** Right axis deviation can be seen in various conditions, including pulmonary embolism, but it is not the most specific or common ECG change.
**Clinical Pearl / High-Yield Fact**
Remember that the S1Q3T3 pattern is a classic sign of pulmonary embolism, but it is not present in all cases. A high index of suspicion and correlation with clinical findings are necessary for diagnosis.
**Correct Answer: C. Right axis deviation.**