During an acute angina episode in the ER, after administration of nitroglycerin, the patient collapses. What is the most likely etiology of the syncope?

• A. Myocardial infarction
• B. Cerebrovascular accident
• C. Aortic stenosis
• D. Orthostatic hypotension

Answer: (C)

Aortic stenosis can cause syncope when a vasodilator is given because of a fixed obstruction to LV outflow. Nitroglycerin reduces preload by venodilation, which lowers the LV volume. In severe aortic stenosis, the left ventricle already struggles to push blood through the narrow aortic valve, so a drop in preload and overall blood pressure markedly decreases stroke volume and cerebral perfusion. The result is a sudden loss of consciousness, often triggered by nitroglycerin in a patient with anginal symptoms. This pattern is more characteristic than cerebral events, orthostatic shifts, or myocardial infarction alone in the setting of a nitro-triggered collapse.