Declining Trend of Sudden Cardiac Death in Younger Individuals: A 20-Year Nationwide Study

Background Declining all-cause and cardiovascular mortality rates have been well-documented, yet temporal trends of sudden cardiac death (SCD) in the young are unclear. We provide contemporary nationwide estimates of the incidence and temporal trends of SCD in the young aged 1-35 from 2000-2019 and evaluate these trends in relation to changes in out-of-hospital cardiac arrest (OHCA) patterns and implantable cardioverter defibrillator (ICD) implantations. Method All individuals aged 1-35 living in Denmark from 2000-2019 were included. Adjudication of SCD cases relied on multiple sources, including death certificates, medical files, and autopsy reports. All OHCA were captured in a nationwide prospective registry, and ICD implantations were registered through administrative registries. Crude and sex- and age-standardized annual incidence rates of SCD were calculated, and temporal changes in SCD incidence were computed as percentage change annualized (PCA). Trends in OHCA survival and characteristics, as well as ICD implantations, were assessed. Results During the 20-year study period (47.5 million person-years), 1 057 SCD were identified (median age 29 years, 69% male sex). The overall incidence of SCD was 2.2 per 100 000 person-years and declined by 3.31% (95%CI 2.42 to 4.20) annually, corresponding to a 49.0% (95%CI 38.7 to 57.6) reduction during the study. Rates of witnessed SCD declined markedly (PCA -7.03% [95%CI -8.57 to -5.48]), but we observed no changes in the rate of unwitnessed SCD (PCA -0.09% [95%CI -1.48 to 1.31]). Consequently, the proportion of unwitnessed SCD increased by 79% (p<0.001). Survival after OHCA in young individuals aged 1-35 increased from 3.9% to 28% in the same time frame, mainly attributable to increased bystander CPR and defibrillation. The implantation rate of ICD increased from 0.76 to 1.55 per 100 000 PY, and the prevalence of young individuals with an ICD increased 16-fold. Conclusion SCD incidence rates in the young declined by 49% over the last two decades. The decline was paralleled by improved survival in OHCA victims and higher ICD implantation rates. However, rates of unwitnessed SCD were unchanged, which calls for new perspectives in preventive strategies. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was supported by an internal grant from the University of Copenhagen, Denmark. However, the university did not influence the study design, data acquisition, data analysis, or article preparation or any effect on the publication process. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study complies with the Helsinki Declaration and was approved by the Regional Data Committee (P-2019-813 and P-2019-523). Registry-based studies on deidentified data are exempt from ethical approvals in Denmark. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data are owned by a third party, and the authors do not have the right to share data; however, upon request, the authors will help in applying to the third party for approval of data sharing.