In acute pulmonary embolism, which among the following is the MOST frequent ECG finding?
**Core Concept**
The underlying principle being tested is the electrocardiographic (ECG) manifestations of acute pulmonary embolism (PE), which is a **blockage of an artery in the lungs**. This condition can lead to various ECG changes due to the sudden increase in pulmonary vascular resistance and subsequent **right ventricular strain**.
**Why the Correct Answer is Right**
The most frequent ECG finding in acute pulmonary embolism is the **sinus tachycardia**, which occurs due to the body's attempt to compensate for the decreased oxygenation and cardiac output. This is a result of the **activation of the sympathetic nervous system** in response to the stress of the pulmonary embolism.
**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because while **atrial fibrillation** can occur, it is not the most frequent ECG finding.
**Option C:** Is incorrect because **ST elevation** is not typically seen in acute PE unless there is associated **myocardial infarction**.
**Option D:** Is incorrect because **complete heart block** is a rare finding in acute PE.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that while ECG changes are common in acute PE, they are often **nonspecific**, making clinical correlation essential for diagnosis.
**Correct Answer:** D. Sinus Tachycardia.