Abstract Body (Do not enter title and authors here): Background
Heart failure (HF) continues to pose a substantial threat to global mortality, exacerbated by the increasing prevalence of atrial fibrillation (AF) among the elderly population in the United States (US). Despite this, AF-related mortality in HF patients aged 65 and above remains understudied. This study aims to analyze the demographic and regional trends of AF-related mortality in the older adults with HF in the US.

Methods
Utilizing death certificates from the CDC WONDER (Centers for Disease Control and Prevention's Wide-Ranging Online Data for Epidemiologic Research) database spanning 1999 to 2020, AF-related mortality in HF patients aged ≥65 years was examined using ICD-10 (International Classification of Diseases 10th Revision) codes. Age-adjusted mortality rates (AAMRs) per 100,000 individuals and annual percentage change (APCs) with 95% confidence intervals (CI) were calculated. Mortality trends were analyzed by year, sex, race/ethnicity, and geographic region.

Results
Between 1999 and 2020, 822,358 AF-related deaths occurred in HF patients aged ≥65 years. The overall AAMR was 88.4 (95% CI: 88.2 to 88.6). Males had higher AAMRs than females (overall AAMRs: 100 vs 80.6). Non-Hispanic (NH) white individuals exhibited the highest AAMR (96.3), followed by NH American Indian or Alaska Native (66.2), NH black or African American (54.2), Hispanic or Latino (46.9), and NH Asian or Pacific Islander (39.4). By census region, the highest AAMRs were in the West (100.8), Midwest (95.7), and Northeast (80.6), with the lowest in the South (80.5). Non-metropolitan areas showed higher AAMRs than metropolitan areas (103 vs 85.2). The top 90th percentile states included Washington, Vermont, Oregon, and Minnesota, with AAMRs nearly double those in the bottom 10th percentile states such as the District of Columbia, Florida, Nevada, and Hawaii.

Conclusion
AF-related mortality trends among older HF patients increased from 1999-2020, with higher AAMRs observed in men, NH White individuals, Non-Metropolitan areas, and the Western region. Targeted strategies addressing precipitating events and further investigations are needed to overcome these trend disparities.