What may cause syncope in a patient with aortic stenosis?

In a patient with aortic stenosis, syncope may occur due to the inability to increase cardiac output during exertion. Aortic stenosis leads to a narrowing of the aortic valve, which obstructs blood flow from the left ventricle into the aorta, especially during physical activity or exertion. When a patient with aortic stenosis exercises, the heart cannot effectively increase the amount of blood pumped due to the fixed obstruction created by the narrowed valve.

This inability to increase cardiac output results in decreased blood flow to the brain, which can lead to syncope, or fainting. Essentially, the body's demand for oxygenated blood outstrips the heart's ability to deliver it when aortic stenosis is present during increased activity levels. Therefore, during exertion, patients may experience dizziness or loss of consciousness because their cardiovascular system cannot compensate adequately for the increased physiological demands.

The other choices do not directly correlate with the pathophysiological mechanisms leading to syncope in this context. Decreased oxygen saturation and peripheral vasoconstriction may influence blood flow or oxygen delivery but do not primarily explain the mechanism of syncope specifically related to aortic stenosis. Increased cardiac output during activity would actually be a normal physiological response; however,