The Fattier Your Heart, the Greater Your Heart Disease Risk

Study links buildup of this hidden fat to heart threat, even in people without symptoms

The amount of hidden fat that collects around the heart may be a stronger indicator of cardiac disease risk than a bulging waistline or flabby thighs, a new study reports.

Heart fat hidden behind the rib cage -- known as pericardial fat -- appears to promote irregular plaque build-up along coronary artery walls that causes atherosclerosis and can trigger heart attacks, the leading cause of death in the United States, according to the study.
"It turns out there are specific areas around the heart where hidden fat seems to be promoting coronary disease, even in people without symptoms," said senior study author Dr. David Bluemke, director of radiology and imaging sciences at the National Institutes of Health Clinical Care.
"This is chest fat you'd never see by looking at someone," he added.
Pericardial fat is linked to being overweight or obese, according to the study in the Aug. 16 online edition of the journal Radiology.
The findings are from the ongoing Multi-Ethnic Study of Atherosclerosis (MESA), a study of 6,800 participants aged 45 to 84 from six communities around the country who had no heart disease at enrollment. In this study, researchers looked at a smaller slice of the volunteers: 89 women and 94 men with an average age of 61 who, although most were overweight, were representative of the general population.
To look for signs of heart disease, the research team used noninvasive MRI to screen for plaque on the walls of the coronary artery and compared it with CT scans of heart fat volume. The NIH-sponsored study highlighted three main findings:

• In people with no symptoms of coronary artery disease, the fat volume of the membrane around the heart is closely associated with the heart artery-clogging plaque found on the MRIs.
• This pericardial fat appears to be more strongly related to coronary artery plaque buildup than is body mass index (a measure of obesity) or waist circumference.
• Examining coronary artery walls through MRIs and CT heart fat scans may be useful in assessing the risk of heart disease.

High-risk patients with chest pain and known coronary risk factors such as obesity should have a traditional angiogram or advanced diagnostic procedures, said Bluemke. "However, low or intermediate risk patients may eventually benefit from understanding that fat deposits around the heart increase their risk of coronary disease," he said.
And while MRI was used as the "gold standard" for NIH research on fat distribution and the dangers of obesity, the expensive procedure isn't necessary in typical patient screening for cardiac risk, Bluemke added.
Bluemke said CT scans are one of the fastest growing medical procedures in the country and may increasingly be used to evaluate coronary artery disease. Scanning often provides data on calcium in the heart vessel, and can calculate a 'fat score' index for tissues around the heart as a best practice procedure that could save lives, he said.
"Two-thirds of the population is overweight or obese and at risk of coronary artery disease and plaque buildup," said Bluemke, noting that extra fat forms "preferentially" in vulnerable areas of the heart of typical overweight patients. "This research says we should be telling doctors about the amount of fat in a patient's chest that shows up on a CT scan, but cannot be seen from outside the body and was previously ignored."
The U.S. Centers for Disease Control and Prevention has declared obesity a national epidemic and a major contributor to the leading causes of death in the United States, including heart disease. Slightly more than one adult in three is obese, and one child in six is obese, the CDC reports.
Dr. Gregg Fonarow, professor of cardiology at UCLA, agrees that CT scans may eventually help doctors determine who is most vulnerable to cardiovascular disease. However, he cautions patients not to rush out for expensive and unnecessary scans or MRI screenings just to find hidden heart fat that might be temporary or not pose a long-term problem.
"The research is really to generate new knowledge and information, not to be a risk predictor or screening tool for the general population," said Fonarow.
An interesting finding is the volume of fat around the heart being positively related to the plaque burden in asymptomatic men and women, most of whom need to shed a few pounds, Fonarow said: "This shows a new reason why overweight people have a higher rate of cardiovascular risk and gives the public another reason to maintain a healthy and active lifestyle."

SOURCES: David A. Bluemke, M.D., Ph.D., director, radiology and imaging sciences, U.S. National Institutes of Health, Bethesda, Md.; Gregg Fonarow, M.D., professor, cardiology, University of California, Los Angeles; Aug. 16, 2011, Radiology, online