Abstract Body (Do not enter title and authors here): Background: Arrhythmias represent a broad spectrum of abnormal heart rhythms that can range from benign to life-threatening. While often associated with older populations, arrhythmia-related morbidity and mortality in younger adults (aged 25-44) remain an important public health concern due to the potential for sudden cardiac death and chronic complications. Understanding how these mortality trends have evolved over time and whether disparities exist by sex and race is critical for developing targeted prevention and intervention efforts. Prior studies have highlighted differences in cardiovascular outcomes across demographic groups, but limited data exist specifically for arrhythmia-related deaths in young adults. This study aims to identify trends and demographic disparities in arrhythmia-related deaths among U.S. young adults.

Methods: Mortality data were obtained from the CDC WONDER database. Arrhythmia-related deaths were identified using ICD-10 codes I47-I49. We calculated age-adjusted mortality rates (AAMRs) per 1,000,000 individuals and evaluated trends over time using Joinpoint regression to estimate annual percent changes (APCs) and corresponding 95% confidence intervals.

Results: A total of 66,250 arrhythmia-related deaths were recorded among young adults during the study period, with 43,033 deaths among men and 23,217 among women. The overall mean AAMR was considerably higher in men (48.2 per million) than in women (26.0 per million). From 1999 to 2018, both sexes experienced a gradual decline in AAMRs (APC for men: -1.64%; women: -1.22%). However, this downward trend reversed between 2018 and 2020, with a notable increase in mortality. Marked disparities were observed across racial and ethnic groups. Non-Hispanic Black men had the highest mean AAMR (87.3), followed by non-Hispanic White men (49.5) and Hispanic men (24.3). Among women, the highest mean AAMR was also seen in non-Hispanic Black individuals (51.4), compared to non-Hispanic White women (26.2) and Hispanic women (10.6). These differences remained consistent over time and were most pronounced in recent years.

Conclusion: Despite earlier improvements, arrhythmia-related mortality among young adults has increased in recent years, particularly after 2018. Men and non-Hispanic Black individuals are disproportionately affected, underscoring the urgent need for targeted public health strategies to reduce these persistent disparities and improve outcomes for at-risk populations.