MRI Of Vessel Wall Thickness Links Pericardial Fat With CVD

Upper frames show minimal pericardial
fat corresponding to minimal plaque
eccentricity in cross-sectional image of
right coronary artery. Lower frames show 
a large amount of pericardial fat with a 
corresponding high degree of plaque
eccentricity in cross-sectional image of right 
coronary artery. (Images used by permission 
of Radiology)

Using MRI to measure plaque in coronary arteries, researchers have determined that fat around the heart is a better predictor of atherosclerosis than BMI and waist circumference in asymptomatic men but not women.

When the researchers made adjustments for BMI, waist circumference, C-reactive protein level and coronary artery calcium content, the relationship between pericardial fat and coronary atherosclerosis remained significant in men but not in women.  (Link to published site)

Senior author Dr. David Bluemke, director of Radiology and Imaging Sciences at the NIH Clinical Center, told The Hub in an e-mail interview that the results remained consistent with early results presented at the American Heart Association (AHA) 2009 Scientific Sessions.

“We did both men and women at that time as well,” Bluemke said. “The effects are larger in men than women. This is usually because at any particular age, women usually act as if they are about 10 years younger than men, with less plaque, lower calcium scores, etc.”

In the current study, the researchers conclude that pericardial fat volume was positively related to coronary atherosclerotic plaque burden in asymptomatic individuals. “This relationship was stronger in men than in women—possibly because of the greater atherosclerotic disease burden in men,” they wrote. The study was published online Aug. 16 in the journal Radiology.

The researchers used a subgroup of 183 participants in the Multi-Ethnic Study of Atherosclerosis, or MESA trial, to determine the relationship between pericardial fat and plaque buildup in coronary arteries. There were 89 women and 94 men with an average age of 61 who took part between October 2005 and February 2008. None had symptoms of atherosclerosis, and all underwent a chest CT scan at the start of the study to assess coronary artery calcification.

Patients then underwent MR angiograms and cross-sectional MR imaging of coronary artery walls. Those with image quality grades 2 or 3 were analyzed by an unblinded observer, who traced the inner and outer coronary walls to measure artery wall thickness. Pericardial fat volumes were measured from the cardiac CT scans. The researchers then compared the atherosclerosis with the calcium scores, C-reactive protein levels and pericardial fat volume.

A total of 387 coronary artery wall images were rated grade 2 or 3 for image quality and evaluated for wall thickness, of these 203 were in men and 184 in women. The men had significantly greater average coronary artery wall thickness, average 2.0 mm compared to 1.9 mm for women. They then looked at the relationship between pericardial fat and plaque eccentricity. Bluemke explained that plaque eccentricity measures the ratio of the thick side of the vessel wall to the normal side.

“Plaque in the arteries forms very irregularly,” Bluemke said. “Usually one side of the vessel has the plaque, the other side is more normal. So one measure of disease, is to look at the ratio of the abnormal thick side, to the more normal thin side,” he said.

No significant difference in mean minimal coronary artery wall thickness or mean coronary plaque eccentricity was observed between the men and women. Nor was there any significant difference in mean wall thickness, mean maximal wall thickness, or mean plaque eccentricity between the left main, left anterior descending, and right coronary arteries.

In the men pericardial fat volume was positively linked to plaque eccentricity. For every increment of 1 standard deviation in pericardial fat volume was associated with a 0.3 increase in plaque eccentricity. In women pericardial fat volume was also positively correlated with plaque eccentricity but not as strongly.

When they controlled for BMI, waist size and coronary calcium scores the relationship between pericardial fat and plaque remained significant in men, but not in women. The researchers theorized that this difference may be that men are at greater risk of for increased plaque.

“Our results in these asymptomatic individuals are consistent with findings in patients with advanced atherosclerotic disease—namely, that a large amount of pericardial fat is significantly associated with measures of atherosclerotic disease,” they concluded.

By Michael O’Leary, contributing writer Health Imaging Hub