Despite a 50 percent drop in the United States’ cardiovascular disease (CVD) mortality rate between 1980 and 2015, it remains the nation’s leading cause of death. A recent analysis of death records and census data of 3,111 counties in the U.S. found that CVD mortality rates varied significantly across the country.

The study, published online May 17 in JAMA, found the largest concentration of counties with high CVD mortality stretched from Oklahoma to eastern Kentucky. Specific CVD conditions, such as atrial fibrillation and endocarditis, were clustered regionally.

“Despite this decline in absolute differences between counties, large differences remained in 2014,” wrote lead author Gregory A. Roth, MD, with the department of medicine at the University of Washington, and colleagues. “These findings suggest major efforts are still needed to reduce geographic variation in risk of death due to ischemic heart disease and cerebrovascular diseases.”

Higher mortality rates for specific CVD conditions were found in specific areas, such as the Northwest for atrial fibrillation, the Midwest for aortic aneurysm, and endocarditis in the Mountain West.

“In contrast to the national trend for CVD mortality rates as a whole, mortality rates due to atrial fibrillation, endocarditis and peripheral arterial disease have increased since 1980,”

Rates of CVD mortality were lowest in areas surrounding San Francisco, Denver, Minneapolis and Miami and in northern Nebraska and northeastern Virginia.

Researchers noted limitations of the study due to error in census and vital statistics data, both of which are subject to error in cause-of-mortality reporting. Still, while nationwide CVD mortality has declined in the last 35 years, some conditions have increased.

In an accompanying editorial, Gregory A. Roth, MD, MPH, with the National Institutes of Health, and two colleagues tout the decrease in CVD mortality as “one of the greatest biomedical research and public health achievements of the 20th century.”

Still, note the authors, the U.S. has one of the highest death rates from CVD compared to other high-income countries—mortality rates that stretch across racial, sex, geography and socioeconomic status. The recent study, though, can be useful in combating CVD mortality across the U.S.

“These state-based, county-level variations are important because understanding their primary determinants can inform not only the types of multilevel and multisector interventions needed but also the level of intensity and the necessary dose required for practices, programs, and policies to have sustained beneficial effects on health,” wrote Roth and colleagues.