Q. A 3-year-old Norwegian male is brought to the emergency department because of a transient loss of consciousness while playing with his older brother. The child was born uneventfully to a 23-year-old mother who had no prenatal care. He is currently being treated with erythromycin for acute tonsillitis. The patient's medical history is significant for iron deficiency anemia and sensorineural hearing loss, which required a cochlear implant at the age of 10 months. His ECG is shown below. Which of the following is the most likely diagnosis?