Review Question - QID 213821

A 67-year-old man presents to the emergency department after an episode of syncope. He was at a baseball game when he suddenly lost consciousness. After about 15 seconds, the patient woke up and was back to his baseline. He was sitting when the episode occurred and currently feels well otherwise. He did not fall or hit his head. He has a past medical history of diabetes, obesity, a myocardial infarction, and dementia. He was also recently treated for an atypical pneumonia and vomiting with azithromycin and ondansetron. The patient states that he actually had another episode similar to this 2 days ago while he was watching television. He states that these episodes come on randomly with no preceding symptoms, and when he wakes up he feels at his baseline. His temperature is 97.6°F (36.4°C), blood pressure is 154/92 mmHg, pulse is 88/min, respirations are 17/min, and oxygen saturation is 98% on room air. Cardiopulmonary exam is unremarkable and reveals a normal S1 and S2 with clear breath sounds. The patient’s cranial nerves are grossly intact, and his gait is stable. An ECG is seen in Figure A. Which of the following is a possible etiology of this patient’s symptoms?