Appropriate therapy for implantable cardioverter defibrillators used as primary versus secondary prophylaxis

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Implantable cardioverter defibrillators (ICD) are used for primary prevention in children highly suspicious of life-threatening arrhythmias due to family history and malignant syncope. This practice might potentially result in a lower incidence of appropriate therapy compared with ICDs implanted for secondary prevention following documented ventricular arrhythmias. PURPOSE: We aimed to compare the rate of appropriate therapy after ICD implantation for primary versus secondary prevention in young children. METHOD: Using national ICD registry, this retrospective nationawide cohort study included children aged ≤15 years who received their first ICD between 1988 and 2020. Patient characteristics, medical history including mortality, device indication, therapy and complications were retrieved from electronic medical files. The primary endpoint was time to appropriate therapy, defined as shock or anti-tachycardia pacing for ventricular tachycardia or fibrillation. RESULTS: During the study period, a total of 81 ICDs (39 ICDs pr. million live births) were implanted. Among these, 79 were included in the outcome analysis due to retrievable follow-up data. At baseline, the majority had channelopathies (44%) or structural heart diseases (42%), whereas 25 (32%) and 54 (68%) devices were implanted as primary and secondary prophylaxis, respectively. The median age at primary implantation was 13.9 and 11.6 years (p<0.05), respectively. During a median follow-up of 9.0 (IQR: 4.8–13.9) years, 44 patients experienced appropriate device therapy and 6 died, with no difference for primary and secondary prevention recipients (p=0.34 and p=0.83). The 10-year cumulative incidence of appropriate therapy was 56% for primary prevention recipients and 68% for secondary prevention recipients, whereas 10-year survival probability was 90% (95% CI: 76-100%) and 81 % (95% CI: 63%-99%), respectively. All deaths were of cardiovascular cause. Bleeding occurred in 0 versus 2, infection in 5 versus 4, and inappropriate shock therapy in 2 versus 11 patients, with an overall combined trend towards more events for ICDs implanted as secondary prophylaxis (p=0.08). CONCLUSIONS: ICD implantation in young children was relatively rare. The rate of appropriate therapy was similar among primary and secondary ICD recipients, indicating too restrictive primary prophylaxis implantation, which should be investigated in future studies. The incidence of complications was highest among secondary ICD recipients. [Figure: see text]