A 22-year-old medical student faints while watching a blood draw. Just before losing consciousness she feels nauseated and warm, and witnesses note pallor. The cardiovascular event responsible for her syncope is:

• A Sudden loss of sympathetic tone with increased vagal outflow causing vasodilation and bradycardia ✓
• B Excessive sympathetic discharge causing intense vasoconstriction and hypertension
• C Primary pump failure of the left ventricle with pulmonary congestion
• D Sustained tachyarrhythmia abolishing atrial contribution to filling

Explanation

Vasovagal (neurocardiogenic) syncope combines emotional triggers with venous pooling; central processing produces abrupt sympathetic withdrawal and vagal activation, causing peripheral vasodilation together with bradycardia. The combination of pallor, warmth and nausea reflects this mixed vasodepressor and cardioinhibitory response. Option B describes the opposite hemodynamic state, and options C and D describe cardiogenic mechanisms unrelated to the situational trigger.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.