Over the last 40 years, heart disease rates have dropped in the U.S. overall, but the changes varied widely by region, with the highest rates of the disease shifting from the Northeast to the South, researchers say.

"Heart disease" refers to several conditions including coronary artery disease, which can cause heart attack. Despite the decline in deaths over time, heart disease is still the leading cause of death in the U.S., killing more than 600,000 people per year, according to the Centers for Disease Control and Prevention (CDC).

"The consistent progression southward over the past few decades suggests that the pattern is not random - and could be attributed to geographic differences in prevention and treatment opportunities," said lead author Michele Casper of the CDC's Division for Heart Disease and Stroke Prevention in Atlanta, Georgia.

"Identifying those counties and regions with the greatest burden of mortality is a necessary first step to target appropriate resources that will ultimately reduce death rates," Casper told Reuters Health by email.

The researchers used data on heart disease deaths among people age 35 and over in the U.S. collected in two year intervals, between 1973 and 2010, from more than 3,000 counties of the 48 contiguous states.

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Every county saw a decline in heart disease deaths. The average decline across the U.S. was 61 percent, but some counties only saw a decline of 9 percent while others cut heart disease deaths by 83 percent.

At the beginning of the study, heart disease deaths were most common in the Northeast through Appalachia and into the Midwest. Coastal North Carolina, South Carolina and Georgia also had high rates.

Most counties with the lowest death rates were located in the West, with some low-rate counties also scattered in Alabama, Florida and Mississippi.

By 2010, most high-rate counties were still in the eastern half of the country, but in the South, rather than in the North, with some parts of New England becoming pockets with lower death rates.

Declines were slowest in counties in Alabama, Mississippi, Louisiana, Arkansas, Oklahoma and parts of Texas, the authors reported in a paper scheduled for publication in Circulation.

Since the 1970s, national attention on the dangers of cigarette smoking and uncontrolled high blood pressure has led to a significant decline in deaths from coronary heart disease and heart attack, but "heart disease" includes other conditions which have not decreased as much, said Dr. Donald A. Barr of Stanford University School of Medicine in California, who wrote an editorial accompanying the new study.

Comparable data for heart failure, which is a different process not due to clogging of blood vessels but due to the heart wearing out as a result of diabetes, obesity and underlying high blood pressure, has not been coming down as fast, Barr told Reuters Health by phone.

"(Heart failure) is projected to increase over the next couple of decades, while coronary heart disease is expected to decline," he said.

Heart failure disproportionately affects low-income Americans and African Americans, he said. "These at-risk populations are found in a somewhat higher proportion in those southeastern states."

"Combining heart failure and coronary heart disease under the global term 'heart disease' combines good news with not so good news," Barr said.

There were still meaningful declines in heart disease deaths in the South, Casper noted.

"Heart disease-related deaths are largely preventable, and with targeted public health efforts, it's possible to alleviate much of the heavy burden of this disease and close the geographic gap in declining heart disease death rates," Casper said. "With collaboration, government agencies, medical care organizations, community groups, businesses and other organizations can provide more local opportunities for physical activity, as well as access to smoke-free spaces, affordable healthy foods, quality healthcare and social and economic well-being."