4th May 2025

A 20-year-old male presents to ED with an episode of collapse.

A 20-year-old male presents to ED with an episode of collapse. The night before he was on a night shift and admitted that he was drinking heavily with his friends at a party. Today while playing football, he experienced breathlessness on exertion and palpitations before collapsing.

He is otherwise normally fit and well. He does not have a family history of any cardiac disease or sudden cardiac death in the family. On initial assessment in ED, he has a normal cardiovascular examination with no displacement of his apex beat. His heart rate is 165 bpm and a blood pressure of 100/80mmhg. His pulse is irregularly irregular. A 12 lead-ECG then shows an irregularly irregular rhythm.

In ED, he then gets treatment for atrial fibrillation with a fast ventricular rate and has a dose of Verapamil. Shortly after this he loses consciousness, and his cardiac monitor shows a broad complex tachycardia.

What is the most likely underlying diagnosis that brought about his first collapse?

Select the SINGLE most appropriate option from the list below. Select ONE option only.