While heart disease death rates have declined overall in the United States, there are dramatic differences in those rates among U.S. counties, including weaker declines found south of the Mason-Dixon Line, according to new research in the American Heart Association’s (AHA) journal Circulation.

The findings reveal a notable geographic shift in death rates from heart disease since the early 1970s, emphasizing the importance of geography for heart disease prevention and treatment, according to Michele Casper, Ph.D., the study’s lead author and an epidemiologist at the Centers for Disease Control and Prevention’s (CDC’s) Division for Heart Disease and Stroke Prevention in Atlanta, Georgia.

“This is the most comprehensive study to compare county-level patterns of geographic disparities in heart disease death rates over an extended timeframe,” Casper said.

Geographic inequality

Researchers studied mortality data from residents 35 years and older in more than 3,000 U.S. counties between 1973 and 2010. In the 1970s, researchers noted that the largest concentration of high death rate counties stretched from the Northeast through parts of Appalachia and into the Midwest, as well as along coastal areas in North Carolina, South Carolina and Georgia. However, by the end of the study period in 2009-2010, those geographic high-rate clusters had shifted south of the Mason-Dixon Line. They also found:

• Declines in heart disease death rates ranged from 9.2 percent to 83.4 percent among U.S. counties in the past four decades.
• Counties with the slowest declines (9.2 to 49.6 percent) were primarily concentrated in Alabama, Mississippi, Louisiana, Arkansas, Oklahoma and Texas.
• The fastest county declines (64.1 to 83.4 percent) were largely found in the northern half of the nation.
• Overall, the magnitude of geographic inequality in heart disease death rates nearly doubled during the course of the study. 

“These findings provide local communities with important historical context regarding their current burden of heart disease, and emphasize the importance of local conditions in heart disease prevention and treatment efforts,” Casper said.

Why the disparities?

Although the study didn’t analyze the reasons behind the death rate disparities, researchers say the findings suggest that there may have been systematic changes in conditions that affect heart disease death rates – such as social and economic conditions, healthy public policies, opportunities for physical activity, promotion of smoke-free environments and access to healthy foods and healthcare.

“Despite the overall decline in heart disease death rates, heart disease remains the leading cause of death in the United States, as well as one of the most widespread and costly health problems facing the nation. More than 600,000 people die of heart disease in the United States every year – that’s one in every four deaths,” Casper said.

One limitation of the study is reliance on death certificates, which can, in some cases, misclassify cause of death.

Co-authors are Michael R. Kramer, Ph.D.; Harrison Quick, Ph.D.; Linda J. Schieb, M.S.P.H.; Adam S. Vaughan, M.P.H., M.S. and Sophia Greer, M.S.P.H. Author disclosures are on the manuscript. The CDC supported this study.