Researchers at Johns Hopkins have evidence to explain
why the supposedly natural act of aging
is by itself a very potent risk factor for life-threatening
heart failure.
In a study presented Nov. 4 at the American Heart
Association's annual Scientific Sessions in
Orlando, Fla., the Johns Hopkins team analyzed more than a
half dozen measurements of heart
structure and pumping function to assess minute changes in
the hearts of 5,004 men and women, ages
45 to 84, of different ethnic backgrounds and with no
existing symptoms of heart disease.
Researchers found that each year as people age, the
time it takes for their heart muscles to
squeeze and relax grows longer, by 2 percent to 5
percent.
Test results were obtained from study participants who
had undergone high-tech magnetic
resonance imaging of the heart, which measures individual
muscle segment changes with each
heartbeat.
The findings, researchers say, offer insight into the
root causes of heart failure. They are
especially valuable now as millions of baby boomers in
America move into their 60s, a time when most
signs and symptoms of heart problems first appear.
Estimates show that more than 5 million Americans have
some form of congestive heart failure,
marked by symptoms such as shortness of breath and
fatigue.
"Our results demonstrate just how the heart plays a
losing game of catch-up as people age,"
said Susan Cheng, who led the study while a medical
resident at Johns Hopkins. "It's an amazing piece
of the puzzle of heart failure that finally singles out the
effects of age over better-known risk
factors, such as high blood pressure, in otherwise healthy
people, and regardless of race."
"We already knew that the heart is constantly trying
to adapt to risk factors, but now we know
that this task gets more difficult as the heart ages and
loses a little bit of its pumping capacity every
year," said Cheng, now a cardiology fellow in Boston.
She says the findings could lead to diagnostic tests
to identify those whose hearts are aging
faster than others, enabling preventive drug therapy,
pacemakers or lifestyle changes to slow or even
reverse the deleterious effects.
Johns Hopkins
cardiologist Joao Lima, the senior study investigator,
says effects of aging have
been hard to determine because of inherent flaws in using
standard criteria to assess heart function.
The current gold standard, he says, is the heart's ejection
fraction, a ratio of the amount of blood
pumped out with each heartbeat to the total volume of blood
available for pumping. An ejection
fraction of 50 percent to 65 percent is considered
normal.
Study results showed that ejection fraction actually
rose by 0.01 percent with every year of
age. But Lima calls this figure misleading because the
total amount of blood available for pumping, the
bottom number in the ratio, decreases as the size of the
heart cavity shrinks and heart walls thicken,
falsely boosting test results when heart function is
actually failing.
When researchers separated the numbers, the actual
amount of blood pumped out by the heart
fell by 8 milliliters per year, says Lima, an associate
professor at the Johns Hopkins School of
Medicine and its Heart Institute.
The flaw in using ratios, he notes, also helped to
mask the gradual shrinkage of heart muscle
mass. Researchers found that heart muscle mass declined by
on average 0.3 grams per year. This
occurred even though heart wall thickness had expanded and
despite an increase in another standard
measure of heart function, the ratio of left ventricular
mass to blood volume, which went up by 5
milligrams per milliliter each year.
Lima says it's important not to be misled by existing
tests for heart function, especially
ejection fraction ratios, when diagnosing patients. He
points out that almost half of the 550,000
Americans newly diagnosed each year with heart failure,
mostly women over age 50, have a nonsystolic
form, in which the ejection fraction appears the same even
though heart function is declining. "Age
could be the deciding factor in determining who gets this
kind of heart failure," he said.
"This study highlights how the aging heart's anatomy
and function change hand in hand over
time, similar to arteries stiffening, bones weakening from
loss of calcium and kidney function
declining," Lima said. "Physicians and patients need to
recognize it as a process that can be
accelerated by risk factors or possibly slowed down by
healthy lifestyle choices and sound medical
care."
The next step, researchers say, is to look for
so-called biological markers, usually blood
proteins, that can track the effects of the aging process
on heart shape and function and to measure
these markers so that a test specific to aging of the
cardiovascular system can be developed.
Study participants from six centers across North
America were drawn from a larger pool of
7,000 ethnically diverse adults, including
African-Americans, Chinese-Americans, Caucasians and
Hispanics, all monitored to see who develops heart failure.
Started in 2000, the Multiethnic Study of
Atherosclerosis is set to run for another six years. 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.
Funding for this study comes from the National Heart,
Lung and Blood Institute, a member of
the National Institutes of Health.
In addition to Lima and Cheng, other Johns Hopkins
investigators involved in this study were
Veronica Fernandes and David Bluemke.
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