Review Question - QID 212739

A 27-year-old woman is brought to the emergency department after passing out at work. She reports that she was standing at a meeting when she felt lightheaded; the next thing she remembers was waking up with her coworkers around her. A coworker who accompanied the patient claims that she bit her tongue during the episode but denies any shaking or jerking. The episode lasted about 15 minutes, and she denies any similar events in the past. Her past medical history includes gastroesophageal reflux disease and asthma, for which she takes cimetidine and an albuterol inhaler, respectively. She is currently taking azithromycin for a chlamydial infection diagnosed 3 days ago. Family history is unremarkable. Physical examination is unremarkable except for mild tachycardia and suprapubic tenderness. An electrocardiogram (ECG) obtained during triage is shown in Figure A. What is the most likely explanation for this patient’s symptoms?