Coronary Artery Calcium Best Predicts CVD in CKD Patients

Jenni Laidman

August 22, 2014

A coronary artery calcium (CAC) score was better able to predict the risk for cardiovascular events among patients with chronic kidney disease (CKD) than either carotid intima-media thickness (IMT) or ankle brachial index (ABI), according to a study published online August 21 in the Journal of the American Society of Nephrology.

To determine which test best predicted cardiovascular disease (CVD), Kunihiro Matsushita, MD, PhD, assistant scientist, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, and colleagues assessed participants enrolled in the Multi-Ethnic Study of Atherosclerosis. The study population included 1284 people with CKD and 5269 without the disease, aged 45 to 84 years, with no history of CVD.

The investigators compared the performance of the calcium score with 2 other measures of subclinical atherosclerosis, IMT and ABI, as predictors for CVD, including coronary heart disease, stroke, heart failure, and peripheral artery disease. Previous studies have found that conventional risk factors are not good predictors of CVD in patients with CKD. Cardiovascular disease is the leading killer among people with CKD, accounting for about half the deaths among people with the chronic condition.

In a median follow-up period of 8.4 years, the researchers identified 650 cardiovascular events, including 236 among patients with CKD.

When the researchers split the CKD group into quartiles based on predictive measures, they found that CAC outperformed the other 2 tests. Specifically, those in the highest quartile of risk based on CAC had a hazard ratio (HR) for CVD of 3.02 (95% confidence interval [CI], 2.03 - 4.50; P < .001) compared with patients in the lowest 2 quartiles. In comparison, patients in the highest quartile for ABI scores had a hazard ratio of 1.63 (95% CI, 1.09 - 2.45; P = .004) compared with those in the lowest quartile. The HR for IMT failed to reach significance in the CKD group.

Among those in the cohort without CKD, the HR in the top quartile for CAC was 4.11 (95% CI, 3.11 - 5.44; P < .001). For IMT, the HR in the top quartile was 1.37 (95% CI, 0.98 - 1.92; P < .01), and for ABI, the HR in the top quartile was 1.60 (95% CI, 1.21 - 2.13; P = .001). The results were adjusted for race, sex, systolic BP, antihypertensive medications, total cholesterol, high-density lipoprotein cholesterol, smoking, and diabetes. The authors report the HRs for third quartile scores for CAC were also statistically significant for both groups.

"Our research is important since it assures the usefulness of coronary artery calcium for better [CVD] prediction in persons with CKD, a population at high risk for [CVD] but with potential caveats for the use of traditional risk factors," Dr. Matsushita said in a news release from the American Society of Nephrology.

The authors point out that exposing patients to 1 mSv ionizing radiation for the CAC test is a concern. "This issue is particularly relevant if follow-up evaluation is required to update CVD risk," they write.

A second issue to consider with CAC testing is cost-effectiveness. IMT and ABI are more widely available at lower cost and do not require radiation exposure. To determine cost-effectiveness, the authors suggest that randomized trials to determine whether risk classification by CAC score followed by lifestyle or pharmacological intervention actually reduced CVD occurrence.

"Our results suggest that CAC is useful to better classify CVD risk in individuals with CKD as well as those without CKD," the authors conclude.

The CAC test has been demonstrated as a superior predictor of coronary heart disease and stroke in the general population. This is the first test of its performance in people with CKD.

This research was supported by the National Heart, Lung, and Blood Institute and the National Center for Research Resources. The authors have disclosed no relevant financial relationships.

J Am Soc Nephrol. Published online August 21, 2014. Abstract

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