In acute pulmonary embolism, the most frequent ECG finding is
**Core Concept**
Pulmonary embolism (PE) can lead to acute right ventricular strain, which manifests as ECG changes. The ECG findings in PE are often nonspecific but can provide crucial clues for diagnosis.
**Why the Correct Answer is Right**
The most common ECG finding in acute pulmonary embolism is the S1Q3T3 pattern. This pattern is characterized by a prominent S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. This pattern is thought to be due to the acute right ventricular strain caused by the pulmonary embolism, leading to a decrease in right ventricular stroke volume and a subsequent increase in right atrial pressure. The increased right atrial pressure causes a right axis deviation, which is reflected in the ECG as a Q wave in lead III.
**Why Each Wrong Option is Incorrect**
* **Option A:** Tachycardia is a common finding in pulmonary embolism, but it is not specific and can be seen in many other conditions. While tachycardia may be present in PE, it is not the most frequent ECG finding.
* **Option B:** The P pulmonale pattern, characterized by a tall P wave in lead II, is not a specific finding for pulmonary embolism. This pattern can be seen in other conditions such as hyperthyroidism or left atrial enlargement.
* **Option C:** The right bundle branch block (RBBB) pattern can be seen in pulmonary embolism, but it is not the most frequent ECG finding. RBBB can be seen in many other conditions, including coronary artery disease or cardiac sarcoidosis.
**Clinical Pearl / High-Yield Fact**
The S1Q3T3 pattern is a classic ECG finding in pulmonary embolism, but it is not present in all cases. A high index of suspicion and a thorough clinical evaluation are necessary to diagnose PE.
**Correct Answer:** S1Q3T3 pattern.