The study was presented on Nov. 4 at the American Heart Association's (AHA) annual Scientific Sessions in Orlando.
For the study, the research team examined 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, age 45 to 84, of different ethnic backgrounds and with no existing symptoms of heart disease. It was 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 - tagged MRI - which measures individual muscle segment changes with each heartbeat. Researchers said that the findings offer insight into the root causes of heart failure. They are especially valuable now as millions of baby boomers move into there 60s, a time when most signs and symptoms of heart problems first appear.
"Our results demonstrate just how the heart plays a losing game of catch-up as people age," said Susan Cheng, M.D., a former medicine resident at Hopkins who led the study. "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," she added.
Cheng said: "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." She added that 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.
Hopkins cardiologist Joao Lima, M.D., the senior study investigator, said that the effects of aging have been hard to determine because of inherent flaws in using standard criteria to assess heart function. He said that the current gold standard 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.
The results of the study showed that ejection fraction actually rose by 0.01 percent with every year. However, Lima called 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.
Lima said, when the team separated the numbers, the actual amount of blood pumped out by the heart fell by 8 millilitres per year. He noted that the flaw in using ratios 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 millilitre each year.
Lima said 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 non-systolic 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.
"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," he added.
Researchers said that the next step is to look for so-called biological markers, usually blood proteins, which 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.