A 24-Year-Old Man Is Evaluated Due to a Syncopal Episode

A 24-year-old man is evaluated due to a syncopal episode that occurred immediately after he completed a 13-mile half-marathon.  The patient felt light-headed and then passed out.  He was immediately placed in a supine position and regained consciousness after 2-3 minutes.  The patient has no chest pain, palpitations, or shortness of breath.  He has never had a similar episode.  There is no family history of sudden death.  The patient does not use alcohol or illicit drugs.  Temperature is 37 C (98.6 F) , blood pressure is 98/56 mm Hg, pulse is 80/min, and respirations are 14/min.  Complete physical examination and ECG show no abnormalities.  Which of the following is the most likely mechanism of this patient's syncope?

A) Decreased cardiac preload
B) Decreased right ventricular contractility
C) Left ventricular outflow obstruction
D) Parasympathetic-mediated bradycardia
E) Tachyarrhythmia due to cardiac irritability

Correct Answer:

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