What is the most common cause of acute mesenteric ischemia?

• A. Hemorrhage
• B. Intestinal obstruction
• C. Atrial fibrillation
• D. Sepsis

Answer: (C)

Acute mesenteric ischemia is primarily caused by a reduction in blood flow to the intestines, and the most common underlying condition leading to this reduction is embolism, typically associated with atrial fibrillation. Atrial fibrillation can result in the formation of thrombi in the left atrial appendage, which can then dislodge and travel to the mesenteric arteries, leading to occlusion and subsequent ischemia of the bowel. This mechanism is significant as it directly correlates with the high incidence of embolism-related events in patients with atrial fibrillation, making it the leading cause of acute mesenteric ischemia.

In contrast, while hemorrhage, intestinal obstruction, and sepsis can contribute to bowel ischemia through various mechanisms, they are not as prevalent as the embolic events caused by atrial fibrillation. Hemorrhage may lead to hypoperfusion but usually does not cause acute mesenteric ischemia in the presence of normal anatomical structures. Intestinal obstruction typically involves mechanical issues rather than vascular compromise, and sepsis, although it can cause ischemia through systemic effects and complications, is far less common as a direct cause of acute mesenteric ischemia compared to embolism from atrial fibrillation.