Apr. 2, 2007 Generally healthy African Americans may be at higher risk of heart failure because of racial variations in heart muscle's pumping ability, a Johns Hopkins study suggests.
Scientists have known for nearly a decade that African Americans have higher rates of hospitalization for heart failure than other major U.S. racial or ethnic groups, but until now they have had limited information other than socio-economic and demographic characteristics to explain why this is so.
In what is believed to be the first, large-scale analysis of racial or ethnic differences in certain kinds of heart function, a team of Hopkins cardiologists found that muscle contraction in three main regions of the heart was on average weaker by 1 percent to 3 percent in African Americans, regardless of age, gender or existing risk factors, such as high blood pressure.
The Hopkins findings are among the first conclusions to emerge from the long-term Multiethnic Study of Atherosclerosis, or MESA for short. MESA is monitoring nearly 7,000 men and women, age 45 to 84, of different ethnic backgrounds and with no existing symptoms of heart disease to determine who develops heart failure and dies from it, and who does not.
In the study, to be presented March 26 at the American College of Cardiology's annual Scientific Sessions in New Orleans, the Hopkins team also found that Chinese Americans' hearts had a consistently, if mildly stronger squeezing function, of a similar magnitude than those of other racial or ethnic groups.
Researchers say that heart disease among Chinese Americans is less of a problem than in African Americans, although there is yet no direct evidence of a protective effect of stronger contraction in Chinese Americans.
Another surprise finding was that hearts in Chinese Americans contract more quickly than those of other ethnic groups. Three of four heart walls were fully squeezed on average 20 milliseconds to 30 milliseconds faster than in Hispanics, and were more than 10 milliseconds faster than in either African Americans or Caucasians.
According to senior study investigator and cardiologist João Lima, M.D., M.B.A., "even without showing symptoms, people can still be at risk of having heart trouble. And a slower or faster heartbeat is not normal."
"Our results show that genetic and racial factors are clues that can be used in early identification of those more vulnerable to coronary artery disease, heart failure, arrhythmias and sudden cardiac death, or those in more need of early treatment - or those at less risk and less likely to need early intervention."
Lima, an associate professor of medicine and radiology at The Johns Hopkins University School of Medicine and its Heart Institute, says MESA has already confirmed for both men and women that changes in one particular region of the heart - the top, front wall of the left ventricle - were linked to the greatest declines in heart function.
Nearly all participants in the MESA study had an initial cardiac magnetic resonance imaging test, and more than 1,100 participants in the six-city investigation had a special, so-called tagged MRI performed. Developed at Hopkins, the computer program better analyzes three-dimensional, computer images of each heart and can track gradual abnormalities during each heartbeat.
For each study participant, calculations measured more than a dozen factors, including thickness of various heart walls, pumping volume, ejection fraction (the percentage of blood pumped from the left ventricle during a heart beat), and shortening fraction (how much the cardiac muscle contracts), and disease risk factors, such as blood pressure (an indicator of the workload or stress on the heart), and body mass index.
Of those tested so far, 73 have developed congestive heart failure, including 31 African Americans, three Chinese Americans, 22 Caucasians and 17 Hispanics. Researchers sorted the results according to racial and ethnic background and for each functional region of the heart fed by its three major arteries.
In each of these three main regions, muscle shortening (or contraction) in African American men and women was weaker than among the other ethnic groups. On average, regional heart function, as measured by the strain on the anterior wall of the heart, showed contraction of 17.5 percent in African Americans, 18.5 percent in Caucasians and Hispanics, and 19.6 percent in Chinese American. Posterior heart contractions were weakest in African Americans, at 12.4 percent, and strongest in Chinese Americans, at 15 percent. Lateral heart function showed similar results, at 20 percent in African Americans, but 21.8 percent in Chinese Americans. Caucasians and Hispanics had numbers that were in between.
"African Americans should be particularly on guard against heart failure, and eventually it may be necessary to do MRI scans or echocardiograms of their adult hearts to evaluate for regional function, or muscle heart strain, if further MESA study results confirm an added risk of eventual cardiovascular disease and death," says lead study author Verônica Fernandes, M.D., Ph.D., a postdoctoral research fellow at Hopkins.
Funding for this multicenter study, which will monitor participants for six to eight years, comes from the National Heart, Lung and Blood Institute, a member of the National Institutes of Health.
Other members of the Hopkins team were Sachin Agarwal, M.D., M.P.H.; Yu-Jen Cheng, M.Sc.; Ciprian Crainiceanu, Ph.D.; Robyn McClelland, Ph.D.; and David Bluemke, M.D., Ph.D.
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