Review Question - QID 216634

A 7-year-old adopted boy presents to the emergency department after fainting. He just switched from being home-schooled to public school and joined the basketball team. He has fainted several times during basketball practices. He did not sustain any injuries or have any prodromes prior to these episodes. He is usually unconscious for less than a minute. He is otherwise healthy and has met all developmental milestones. He does not currently take any medications. His temperature is 97.6°F (36.4°C), blood pressure is 104/54 mmHg, pulse is 100/min, respirations are 19/min, and oxygen saturation is 98% on room air. Physical exam reveals a well-appearing and playful boy. An ECG is performed as seen in Figure A. An echocardiogram is ordered and pending. Which of the following is the most likely diagnosis?