Abstract Background The diagnostic work‐up for cardiac arrest from ventricular tachyarrhythmias occurring in younger adults and structurally normal hearts is variable and often incomplete. Methods We reviewed records for all recipients of a secondary prevention implantable cardiac defibrillator (ICD) younger than 60 years at a single quaternary referral hospital from 2010 to 2021. Patients with unexplained ventricular arrhythmias (UVA) were identified as those with no structural heart disease on echocardiogram, no obstructive coronary disease, and no clear diagnostic features on ECG. We specifically evaluated the adoption rate of five modalities of “second‐line”?cardiac investigations: cardiac magnetic resonance imaging (CMR), exercise ECG, flecainide challenge, electrophysiology study (EPS), and genetic testing. We also evaluated patterns of antiarrhythmic drug therapy and device‐detected arrhythmias and compared them with secondary prevention ICD recipients with a clear etiology found on initial assessment. Results One hundred and two recipients of a secondary prevention ICD under the age of 60 were analyzed. Thirty‐nine patients (38.2) were identified with UVA and were compared with the remaining 63 patients with VA of clear etiology (61.8). UVA patients were younger (35.6?±?13.0?vs. 46.0?±?8.6 years, p?
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