**Question:** Acute Aortic regurgitation is seen in all of the following except -

A. Marfan syndrome
B. Bicuspid aortic valve
C. Coronary artery disease
D. Endocarditis

**Core Concept:**
Acute aortic regurgitation is a sudden onset of severe aortic regurgitation due to dysfunction of the aortic valve. It is a critical emergency situation that requires immediate attention and management. The most common causes are endocarditis, dissection, or rupture of the aortic valve leaflets. Marfan syndrome, bicuspid aortic valve, and coronary artery disease are less common causes, while they may present with aortic regurgitation, they are not the primary causes of acute onset of severe aortic regurgitation.

**Why the Correct Answer is Right:**
Acute aortic regurgitation is typically caused by endocarditis, dissection, or rupture of the aortic valve leaflets. These causes lead to rapid deterioration of the aortic valve function. In contrast, Marfan syndrome, bicuspid aortic valve, and coronary artery disease usually present with chronic regurgitation or aortic stenosis rather than acute onset.

**Why Each Wrong Option is Incorrect:**

A. Marfan syndrome: Although aortic regurgitation can occur in Marfan syndrome, it is not the primary cause of acute onset of severe aortic regurgitation. The condition typically presents with progressive aortic dilatation and regurgitation, but not the sudden onset seen in acute aortic regurgitation.

B. Bicuspid aortic valve: Bicuspid aortic valve is a congenital abnormality, which can lead to aortic regurgitation over time. However, it is less likely to cause acute onset of severe aortic regurgitation due to the gradual development of regurgitation.

C. Coronary artery disease: Coronary artery disease may lead to aortic regurgitation, but it is less likely to cause acute onset of severe aortic regragitation. Coronary artery disease typically presents with angina, myocardial infarction, or sudden cardiac death, rather than acute onset of aortic regurgitation.

D. Endocarditis: Endocarditis is one of the primary causes of acute onset of severe aortic regurgitation due to the infection-induced inflammation, destruction, or perforation of the aortic valve leaflets.

**Clinical Pearl:**
In cases of suspected acute aortic regurgitation, a thorough clinical evaluation should focus on ruling out endocarditis as the primary cause. If endocarditis is ruled out, further investigations should be directed towards identifying the primary cause of aortic regurgitation to guide appropriate management and treatment.