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 socioeconomic factors, age,
gender, smoking, family history and other health problems,
as well as diabetes and hypertension.
The Johns Hopkins team presented its findings March 27
at the American College of Cardiology's annual Scientific
Sessions in New Orleans.
In the study, researchers monitored nearly 7,000 men
and women, ages 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 (one case per
1,000 per year) and almost twice that of Caucasians (2.4
cases per 1,000 per year).
However, when researchers used statistical techniques
to exclude the two traditional risk factors for heart
disease, 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 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," said senior study investigator Joao
Lima, an associate professor of
medicine and
radiology at the School of Medicine and its
Heart Institute.
According to Lima, these early results add to other
interesting findings from the so-called Multiethnic Study
of Atherosclerosis, known as 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 high
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 said.
"African-Americans are clearly getting heart failure from
causes other than heart attack."
According to lead researcher Hossein Bahrami, 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 Johns
Hopkins, says that 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 that 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. 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 part of the National
Institutes of Health.
Another Johns Hopkins investigator involved in this
study, in addition to Lima and Bahrami, was David Bluemke.
Study co-authors were Richard Kronmal, of the University of
Washington; Kiang Liu, of Northwestern University; and
Gregory L. Burke, of Wake Forest University.
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