A 40 year old Asian man presents for a routine adult check-up and because his father, paternal grandfather, and paternal uncle all died of sudden cardiac death in their sleep before the age of 40, an EKG is taken. A shows a normal EKG. B shows this patient's EKG. The cardiac review of systems is notable for an episode of unexplained syncope a few months ago.
Challenge: This is a rare cause of sudden cardiac arrest in a heart without a structural defect. What is it?
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