Radiology: Study questions calcium scoring for African Americans

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Calcified and noncalcified plaque by CCTA. Source: Fabian Bamberg, MD, University of Munich

Despite similar overall burdens of atherosclerotic plaque and stenosis, African Americans may have less stable lesions than whites due to significantly higher volumes of noncalcified plaque, according to a study published June 21 in Radiology, leading experts to suggest that coronary CT angiography may be a more appropriate screening study than calcium scoring among African Americans.

Facing higher risks of diabetes and coronary artery disease (CAD), African Americans suffer from higher disease-specific mortality than whites. Previous research has indicated that the composition of atherosclerotic plaques among blacks differs from whites, showing lower levels of calcium among African Americans.

“Histopathologic studies have revealed that atherosclerosis is less characterized by calcium deposition and vascular remodeling in African Americans than in white individuals, suggesting that there are pathogenetic differences between these populations that are insufficiently reflected by the coronary artery calcium burden,” explained John W. Nance, Jr., MD, from the Heart and Vascular Center at the Medical University of South Carolina in Charleston, and colleagues.

“Plaque composition is an important determinant of lesion vulnerability,” Nance and co-authors continued. The researchers reviewed CT angiography images from 150 African Americans and 151 whites who presented with acute chest pain and intermediate risk of CAD. In addition to comparing the prevalence and extent of atherosclerotic lesions, the authors used an automatic plaque analysis algorithm to quantify the volume of noncalcified plaque on the left main, left anterior descending, left circumflex and right coronary arteries.

African Americans and whites exhibited no significant differences in the presence of either plaque or stenosis. However, whites showed significantly higher prevalence and extent of calcified plaque compared with African American patients, who had higher prevalence and extent of noncalcified plaque.

Ninety-six of the 150 African Americans had a noncalcified plaque on CT, compared with 62 of the 151 whites in the study, amounting to a median noncalcified plaque volume of 2.2 milliliters for blacks and 1.4 milliliters for whites. In contrast, CT revealed calcified plaques in 68 whites but only 39 blacks.

After adjusting for differences in diabetes, hypercholesterolemia and body mass index, these findings persisted, with blacks showing a 2.4-fold higher risk of noncalcified plaque; whites had a 2.2-fold higher risk of calcified plaque.

The authors stated that because calcium scoring excludes noncalcified plaques, their findings should spur a re-examination of the test’s importance for African Americans. “The results of coronary artery calcium scoring studies are to be treated with caution in African Americans, because they may not reflect the true extent of cardiovascular disease,” said U. Joseph Schoepf, MD, professor of radiology and medicine and director of cardiovascular imaging at the Medical University of South Carolina.

“For African American patients, coronary CT angiography may be a more appropriate screening tool for cardiovascular risk,” Schoepf said. The authors supported Schoepf’s proposition by referencing “well-recognized” race-associated differences in cardiovascular disease and atherosclerosis, including studies that have previously shown differences in the composition of atherosclerotic plaques between the two populations.

“Understanding the mechanism behind these disparities may improve the prevention, risk stratification and management of CAD,” Nance and co-authors wrote. As a result, the authors appealed to the importance of larger, prospective and randomized studies to evaluate the capability of coronary CT angiography to predict adverse events based on the characteristics of plaques and their relationships to race.
Nance and colleagues concluded that the higher rate of noncalcified plaque found in African Americans “may be more unstable” and likely reflects differences in disease pathogenesis and natural history that reach beyond individual lifestyle.