County-Based Median Income Level and Acute MI Mortality

Study Questions:

Dose incidence of acute myocardial infarction (AMI) and associated mortality differ by geographic region (specifically county-based median income level) in the United States?


This observational study included Medicare beneficiaries (ages 65 years or older) who were hospitalized for AMI between January 1999 and December 2013. Counties were stratified by median income percentile using 1999 US Census Bureau data adjusted for inflation: low- (<25th), average- (25th-75th), or high- (>75th) income groups. Risk was standardized by age, sex, and race. Outcomes included incident AMI hospitalizations, and 1-year mortality rates.


Over the 15-year study period, AMI hospitalizations and associated mortality rates decreased in all three county income groups. Compared with high-income counties, low-income counties experienced higher mean hospitalization rates in 1999 (1,353 vs. 1,123 per 100,000 person-years, respectively) and in 2013 (853 vs. 648 per 100,000 person-years, respectively). One-year mortality rates after hospitalization for AMI were similar across county income groups, decreasing from 1999 (31.5%, 31.4%, and 31.1%, for high-, average-, and low-income counties, respectively) to 2013 (26.2%, 26.1%, and 25.4%, respectively). Income was associated with county-level, risk-standardized AMI hospitalization rates, but not mortality rates. Increasing 1 interquartile range of median county consumer price index–adjusted income ($12,000) was associated with a decline in 46 and 37 hospitalizations per 100,000 person-years for 1999 and 2013, respectively; interaction between income and time was 0.56. The rate of decline in AMI hospitalizations was similar for all county income groups; however, low-income counties lagged behind high-income counties by 4.3 (95% confidence interval, 3.1-5.9) years. There were no significant differences in trends across geographic regions.


The investigators concluded that hospitalization and mortality rates of AMI declined among counties of all income levels, although hospitalization rates among low-income counties lag behind those of the higher income groups. These findings lend support for a more targeted, community-based approach to AMI prevention.


Declines in AMI incidence were observed among all geographic-income levels, which suggests a diffusion of quality of care; however, differences in mortality rates suggest a continued need to improve long-term care for low-income communities.

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