Scope and Outcome of Early Repolarization Syndrome in Unexplained Cardiac Arrest: Insights From the National HiRO Registry

BACKGROUND: Early repolarization syndrome (ERS) is diagnosed in survivors of unexplained cardiac arrest (UCA) who exhibit a distinct ECG pattern of early repolarization (ER), defined as J-point elevation ≥0.1 mV in ≥2 contiguous inferolateral leads. UCA survivors without ER or another identifiable cause are classified as idiopathic ventricular fibrillation (IVF). This study evaluated long-term outcomes in ERS compared with IVF. METHODS: This retrospective cohort study analyzed patients from the CASPER (Cardiac Arrest Survivors with Preserved Ejection Fraction Registry) who survived UCA and had structurally normal hearts with an Implantable Cardioverter Defibrillator. Of 709 patients, 186 with explanatory diagnoses and no ER pattern were excluded. The remaining 523 were categorized as ERS (n=48), IVF (n=463), or UCA with ER plus an additional diagnosis (Dx+ER, n=12). Patients were followed for the primary outcome of appropriate Implantable Cardioverter Defibrillator therapy, and logistic regression identified predictors of arrhythmia recurrence. RESULTS: Corrected QT interval intervals were significantly shorter in ERS than in IVF (412±25 ms versus 431±41 ms; P <0.01). Over a median follow-up of 5.6 years, appropriate Implantable Cardioverter Defibrillator interventions occurred in 23% of ERS and 13% of IVF patients ( P =0.09), with incidence rates of 3.0 and 1.5 per 100 person-years, respectively. Four deaths occurred (0.8%), with no significant difference between groups ( P =0.39). In Dx+ER, appropriate Implantable Cardioverter Defibrillator therapies occurred in 42% of patients (incidence rate, 4.5 per 100 person-years). Arrhythmia-free survival was lower in ERS than in IVF ( P =0.03). After adjusting for age, sex, and ethnicity, ER was an independent predictor of arrhythmia recurrence (odds ratio, 2.59 [95% CI, 1.33–4.85]; P =0.004). CONCLUSIONS: ERS is associated with shorter corrected QT interval intervals and reduced arrhythmia-free survival compared with IVF, with an incidence rate of 3.0 per 100 person-years. These findings underscore the importance of careful ECG review in patients with apparent UCA, to detect ER and undertake individualized risk assessment in affected individuals.