Which of the following is a common etiology of syncope?

Neurally mediated causes are a frequent etiology of syncope because they involve mechanisms that lead to a sudden decrease in heart rate or blood pressure, resulting in diminished cerebral perfusion. This type of syncope often occurs in younger patients and can be triggered by various stimuli, such as standing up quickly, emotional stress, or certain physical activities.

Common examples of neurally mediated syncope include vasovagal syncope, where an event causes excessive vagal tone, leading to bradycardia and hypotension. This type of syncopal episode is typically temporary and resolves quickly with measures to restore blood flow to the brain, such as lying down.

The other options, while related to syncope, are less common as primary etiologies. Vasculitis generally affects the blood vessels and can lead to other complications but is not a direct cause of syncope. Structural heart defects may lead to syncope due to impaired cardiac function but are less common than neurally mediated causes. Coronary artery disease often contributes to syncope through mechanisms like myocardial ischemia, but again, this tends to be more chronic and associated with other cardiac symptoms rather than being a leading cause of syncope in a broader sense.