Syncope in a young woman

A previously well and active 25 year old woman with no underlying structural heart disease presented with recurrent episodes of new onset syncope over a period of six hours. Her pulse was irregularly irregular at a rate of 230 beats/min. She was hypotensive with a blood pressure of 80/60 mm Hg. Twelve lead surface electrocardiogram (ECG) taken on admission is shown in fig 1. She was immediately electrically cardioverted to sinus rhythm with 150 J. She reported no history of recreational drug use or family history of sudden cardiac death.