Background--Cardiac arrest with preserved left ventricular function may be caused by uncommon genetic conditions. Although these may be evident on the ECG, long-term monitoring or provocative testing is often necessary to unmask latent primary electrical disease.

Methods and Results--Patients with unexplained cardiac arrest and no evident cardiac disease (normal left ventricular function, coronary arteries, and resting corrected QT) underwent pharmacological challenge with adrenaline and procainamide infusions to unmask subclinical primary electrical disease. Family members underwent noninvasive screening and directed provocative testing on the basis of findings in the proband. Eighteen patients (mean±SD age, 41±17 years; 11 female) with unexplained cardiac arrest were assessed. The final diagnosis was catecholaminergic ventricular tachycardia (CPVT) in 10 patients (56%), Brugada syndrome in 2 patients (11%), and unexplained (idiopathic ventricular fibrillation) in 6 patients (33%). Of 55 family members (mean±SD age, 27±17 years; 33 female), 9 additional affected family members were detected from 2 families, with a single Brugada syndrome patient and 8 CPVT patients.

Conclusions--Provocative testing with adrenaline and procainamide infusions is useful in unmasking the etiology of apparent unexplained cardiac arrest. This approach helps to diagnose primary electrical disease, such as CPVT and Brugada syndrome, and provides the opportunity for therapeutic intervention in identified, asymptomatic family members who harbor the same disease.