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

Abstract 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. Clinical Perspectives What is new? (max 100 words, 2-3 bullets) Over the past 20 years, the incidence of SCD in young individuals aged 1–35 declined by 49%. Concomitantly, the 30-day survival after OHCA increased from 4% to 28%, driven by improved bystander CPR rates reaching +80%, and ICD implantations in young adults increased markedly. We observed no decline in the incidence of unwitnessed SCD during the study period. What are the clinical implications (max 100 words, 2-3 bullets) As the majority (73%) of SCD in the most recent years were unwitnessed, preventive strategies targeting unwitnessed cardiac arrests need further attention. Incorporating connected devices, e.g. smart watches, in prevention could potentially help identify ventricular arrhythmias and thus improve survival among unwitnessed cardiac arrest. Low bystander AED rates (8%) call for further improvement in early AED deployment.