Diabetes and high blood pressure, two conditions rooted in genetics and environmental surroundings, play a much greater role than race alone in determining who is mostly likely to develop heart failure, according to the latest study from cardiologists at Johns Hopkins. Each year, nearly 300,000 Americans die from heart failure.
Experts say that racial disparities have long been known to exist in who actually develops risk factors for the condition, with African Americans nearly twice as likely to be diagnosed with diabetes and more than a third as likely to have high blood pressure than Caucasian Americans. But researchers have only now determined the precise role played by race in comparison to other risk factors, including socio-economic factors, age, gender, smoking, family history, and other health problems, as well as diabetes and hypertension.
The Hopkins team will present its findings March 27 in New Orleans at the American College of Cardiology's annual Scientific Sessions in New Orleans.
In the study, researchers monitored nearly 7,000 men and women, age 45 to 84, of different ethnic backgrounds and with no existing symptoms of heart disease. African Americans developed heart failure at significantly higher rates (4.6 cases per 1,000 per year) than all other races, including Hispanics and Caucasians. Their rate was almost five times that of Chinese Americans (1 case per 1,000 per year) and almost twice that of Caucasians (2.4 cases per 1,000 per year).
However, these apparent risk differences among races almost disappeared (dropping from twice as likely, a significant difference, to no more than one-and-a-half times as likely, an insignificant difference) when researchers used statistical techniques to exclude the two traditional risk factors for heart disease.
"When all major factors are taken into account, the differences between races for heart failure largely evaporate in the absence of diabetes and hypertension among African Americans," says senior study investigator João Lima, M.D.
According to Lima, an associate professor of medicine and radiology at The Johns Hopkins University School of Medicine and its Heart Institute, these early results add to other interesting findings from the so-called Multiethnic Study of Atherosclerosis (MESA).
The study, started in 2001, is monitoring its ethnically diverse participants for six to eight years to see who develops heart failure and who does not. It is the first large-scale analysis of racial or ethnic differences in heart function. So far, 79 study participants have developed congestive heart failure.
Other results presented at the meeting showed differences among races in heart strain, or contraction, which may contribute to disparities in heart failure, albeit to a lesser extent. Indeed, African American hearts were found to contract less strongly than those of Hispanic, Caucasian or Chinese American backgrounds.
Lima cautions, however, that much remains to be understood about the root causes of racial disparities and how to fix them.
He points out that while African Americans are at much higher risk of heart failure, there is no similarly higher number for risk of suffering heart attack, which, like diabetes and hypertension, often leads to heart failure.
In MESA, researchers found a reverse relationship, with African Americans having the lowest rates of heart failure due to myocardial infarct (at 25 percent), while other races had a much higher proportion: Caucasians (40 percent), Hispanics (42 percent), and Chinese Americans (100 percent.)
Lima says the difference could be due to successful disease prevention efforts among all racial groups, except for African Americans, at controlling hypertension.
"A lot of public health attention has already been paid to getting high blood pressure under control, so it may be just that this risk factor is under tighter control in some ethnic groups than in others," he says. "African Americans are clearly getting heart failure from causes other than heart attack."
According to lead researcher Hossein Bahrami, M.D., M.P.H., the message to physicians is clear, "warding off heart failure in African Americans requires aggressive treatment of diabetes and hypertension. Whether through increased screening or greater emphasis on drug therapies, these are two risk factors that must be brought under control."
Bahrami, a senior cardiology research fellow at Hopkins, says removing barriers for African Americans to controlling their diabetes and hypertension could be critical to reducing new cases of heart failure. Across all ethnic groups, an estimated 550,000 Americans are diagnosed each year.
Bahrami says the team's next steps are to determine why different rates exist for these risk factors and the role played by biological and environmental factors.
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Funding for this study, which is taking place in six centers in the United States, comes from the National Heart, Lung and Blood Institute, a member of the National Institutes of Health.
Besides Lima and Bahrami, another Hopkins investigator involved in this study was David Bluemke, M.D., Ph.D. Study co-authors were Richard Kronmal, Ph.D., from the University of Washington in Seattle; Kiang Liu, Ph.D., from Northwestern University in Chicago, and Gregory L. Burke, M.D., M.S., from Wake Forest University in Winston-Salem, N.C.
(Presentation title: Race, ethnicity and incident congestive heart failure, the Multiethnic Study of Atherosclerosis.)