Noncalcified Plaque a Strong Indicator of Future Cardiac Events

Becky McCall

March 15, 2011

March 15, 2010 (Vienna, Austria) — Coronary artery plaques, characterized by coronary computed tomography angiography (cCTA), strongly predict major adverse coronary events (MACE), independent of cardiovascular risk factors. This information might aid in risk stratification and choice of therapy for patients with acute chest pain.

John W. Nance, MD, from the Medical University of South Carolina, Charleston, reported his team's findings here at the European Congress of Radiology 2011.

He said that cCTA provides excellent anatomy of the arteries and atherosclerotic disease, but that the prognostic value of cCTA in patients with acute chest pain is less well established, particularly regarding the specific morphologic characteristics of plaques (calcified, mixed, or noncalcified).

"This may be relevant because not all plaques are created equal. Specifically, those with fibrous caps and necrotic inflammatory cores . . . are more likely to rupture, causing acute myocardial infarction," Dr. Nance told Medscape Medical News.

The study aimed to determine the prognostic value of cCTA plaque characterization in patients presenting with acute chest pain. Dr. Nance and his colleagues reviewed the charts of 2682 patients who had undergone cCTA, and included 460 in the study; mean follow-up was 16.7 ± 10.8 months.

All patients received contrast-enhanced retrospective electrocardiogram-gating cCTA with a dual-source computed tomography (CT) scanner. The primary end point was combined MACE, including cardiac death, nonfatal myocardial infarction, unstable angina, and revascularization (coronary artery bypass graft/stent).

For the evaluation, the researchers used an American Heart Association 15-segment model to compile a coronary artery tree. The presence and extent (number of segments) of the following were recorded: any plaque, obstructive plaque with stenosis greater than 50%, calcified plaque, mixed plaque, and noncalcified plaque.

For statistical analysis, CT characteristics were analyzed as both binary and continuous variables, such as the presence or absence of plaques and the number of segments involved by plaque type. Cox regression was used for outcome analysis, which included univariate analysis of clinical risk factors and cCTA characteristics to identify potential predictors of MACE in each group. Multivariate regression analysis was then performed to identify cCTA predictors of MACE, independent of clinical risk factors.

"On univariate cCTA analysis, we found that the presence of all plaque types examined were significant predictors. Also, the extent of all plaque types examined had a statistically significant hazard ratio," reported Dr. Nance.

On multivariate analysis, which accounted for specific clinical and demographic risk factors, the researchers found that the presence of noncalcified plaque was the strongest predictor of MACE, but Dr. Nance stressed that all types were significant predictors. In addition, the extent of noncalcified plaque was the strongest predictor, followed by obstructive, mixed, and calcified plaque. Furthermore, survival curves revealed that for any plaque, cCTA had 100% negative predictive value when plaque was absent.

On the basis of these findings, the researchers concluded that coronary artery plaque burden strongly predicts MACE, independent of cardiovascular risk factors. He added that specific plaque characteristics and subtypes might indicate different cardiovascular risks, and that consideration of cCTA findings might help guide individualized risk stratification and intervention.

"In the future, we would like to further examine the relationship between cCTA findings and histopathology and refine the correlation between plaque type and cardiovascular prognosis. The most commonly used grading scheme for plaque morphology is the one we use — calcified, mixed, and noncalcified — but the American Heart Association's subcategorization of plaque types is significantly more complicated," he said.

Moderating the session, Friedrich D. Knollmann, MD, PhD, associate professor of radiology, University of Pittsburgh, Pennsylvania, asked for Dr. Nance's opinion on the clinical significance of calcified vs noncalcified plaque. Dr. Nance replied that he believes different risks are associated with different plaque types — specifically, nonstenotic plaques are more likely to rupture than stenotic plaques. "Based on our data here, nonobstructive plaque is actually more dangerous than obstructive plaque. This isn't actually emphasized in clinical reports at this point in time," Dr. Nance said.

Filippo Cademartiri, MD, from the University Hospital of Parma, Italy, commented on the study and the issues around the use of cCTA for stratifying and managing patients based on this characterization. "cCTA provides us with an excellent opportunity to visualize coronary arteries with a low radiation dose. Most of the time, life-threatening chest pain is linked to coronary arteries, whether acute [myocardial infarction], acute aortic dissection, or pulmonary embolism. Chest pain may be a killer, so high technology, costs, and improved methods are justified," he said.

"This study using characterization of plaques suggests that noncalcified plaque burden is a strong prognostic indicator of cardiac events, but the results need to be confirmed in large prognostic studies," Dr. Cademartiri told Medscape Medical News.

However, he drew attention to the fact that there are important and growing issues with cCTA. "Should we be performing cCTA on all patients who come to the [emergency department] with chest pain? Obviously no, because we have so many patients and disease prevalence is low. However, when we do perform cCTA, we need to stratify patients to improve outcomes. To do this, we need more highly trained radiologists, whether stratification is by characterization or other means," Dr. Cademartiri noted.

Dr. Nance, Dr. Knollmann, and Dr. Cademartiri have disclosed no relevant financial relationships.

European Congress of Radiology (ECR) 2011: Abstract B-492. Presented March 6, 2011.

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