Profound Vagal Tone and Bradycardia Mimicking Asystole: A Resuscitation Case Report.

A 48-year-old man presented with dizziness. When he arrived at the emergency department, he collapsed and became pulseless. Prior to his collapse, he was asymptomatic and now even participated in multiple marathon and ultra-running events per year. However, he previously experienced a vasospastic inferior STEMI eight years prior from cocaine use. As a result, he had an ischaemic cardiomyopathy with LVEF of 45%. He never took any further illicit substances after the STEMI; instead, he changed his lifestyle completely and commenced extreme endurance sports. After one hour of alternations between VF/VT rhythms and asystole, a rhythm check demonstrated a single complex with a corresponding pulse. He had received 12 mg of epinephrine up to that point as per local resuscitation guidelines. Upon diagnosing extreme bradycardia, 2 mg of total atropine administration resulted in ROSC. We theorise that this bradycardia was a result of increased vagal tone as ROSC was quickly achieved following atropine administration.