A 24-year-old male university student is brought to the Emergency Department by ambulance after a witnessed cardiac arrest. He was playing in a recreational basketball game when he suddenly collapsed. A bystander, a trained off-duty paramedic, immediately initiated cardiopulmonary resuscitation (CPR). An automated external defibrillator (AED) was retrieved from the gymnasium, which advised and delivered a single shock. This resulted in a return of spontaneous circulation. The patient was intubated by the arriving paramedics for airway protection.

He has no significant past medical history and his last annual athletic physical was unremarkable. He takes no medications. He denies smoking, recreational drug use, or use of performance-enhancing supplements. He drinks alcohol socially. There is a family history of a paternal uncle who died suddenly at age 35 from a presumed “heart attack,” but no autopsy was performed. Initial laboratory studies in the emergency department are as follows:

WBC: 9,800/mm³ (4,500-10,000)

Hemoglobin: 15.1 g/dL (13.5-17.5)

Hematocrit: 45% (41-53)

Platelets: 250,000/mm³ (150,000-400,000)

Na⁺: 140 mEq/L (136-146)

K⁺: 4.2 mEq/L (3.5-5.0)

Cl⁻: 101 mEq/L (95-105)

HCO₃⁻: 22 mEq/L (22-28)

BUN: 15 mg/dL (7-18)

Creatinine: 0.9 mg/dL (0.6-1.2)

Glucose: 110 mg/dL

Calcium: 9.5 mg/dL (8.4-10.2)

Magnesium: 2.1 mg/dL (1.7-2.2)

Troponin T (initial): 0.08 ng/mL (<0.01)

Urine toxicology screen: Negative