Coronary Calcium Better than CRP to Stratify Risk
By Todd Neale, Senior Staff Writer,
Published: August 18, 2011
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco.
Among asymptomatic individuals with normal LDL cholesterol levels and elevated high-sensitivity C-reactive protein (hsCRP), measuring the burden of calcium in the coronary arteries with cardiac CT appears to stratify the risk of cardiovascular disease, researchers found.
The estimated rate of cardiovascular disease events through a median of 5.8 years was 2.12% for those with a coronary artery calcium (CAC) score of 0, 4.86% for those with a score of 1 to 100, and 13.65% for those with a score greater than 100, Michael Blaha, MD, of Johns Hopkins University in Baltimore, and colleagues reported in the Aug. 20 issue of The Lancet.
Looking further at patients with both low and high levels of hsCRP, the researchers found that CAC score -- but not hsCRP -- was associated with the risk of coronary heart disease events and overall Action Points
Explain that among asymptomatic individuals with normal LDL cholesterol levels and elevated high-sensitivity C-reactive protein (hsCRP), measuring the burden of calcium in the coronary arteries with cardiac CT appears to stratify the risk of cardiovascular disease.
Point out that in patients with both low and high levels of hsCRP, the researchers found that CAC score -- but not hsCRP -- was associated with the risk of coronary heart disease events and overall cardiovascular events.
cardiovascular events.
Action Points
Explain that among asymptomatic individuals with normal LDL cholesterol levels and elevated high-sensitivity C-reactive protein (hsCRP), measuring the burden of calcium in the coronary arteries with cardiac CT appears to stratify the risk of cardiovascular disease.
Point out that in patients with both low and high levels of hsCRP, the researchers found that CAC score -- but not hsCRP -- was associated with the risk of coronary heart disease events and overall cardiovascular events.
CAC score "could be used to target subgroups of patients who are expected to derive the most, and the least, absolute benefit from statin treatment," Blaha and colleagues wrote. "Focusing of treatment on the subset of individuals with low LDL cholesterol with measurable atherosclerosis might represent a more appropriate allocation of resources, reduce overall healthcare cost, and prevent the occurrence of a similar number of events."
But evidence from randomized trials that such an approach -- which remains controversial -- would actually reduce cardiovascular events in asymptomatic individuals is lacking.
Steven Nissen, MD, of the Cleveland Clinic, pointed out in an email to ABC News and MedPage Today that calcium scanning has never been shown to reduce the risk of MI or death. He called the practice "one of the worst examples of 'medicine gone wild,'" pointing to unacceptable radiation doses and the greater use of unnecessary catheterization and stenting following a scan.
Other physicians contacted, however, supported the use of CAC scoring.
"Use of CAC is helpful in saying if the process of atherosclerosis has started, and is helpful in choosing between lifestyle intervention versus lifestyle intervention plus statin therapy," wrote Christopher Cannon, MD, of Brigham and Women's Hospital in Boston.
The basis of the current analysis was the JUPITER trial, which showed that treatment with rosuvastatin (Crestor) reduced MI, stroke, and cardiovascular death in patients with normal LDL cholesterol levels but elevated hsCRP.
Blaha and colleagues identified a JUPITER-like cohort in the Multi-Ethnic Study of Atherosclerosis (MESA) to determine whether measuring CAC would stratify patients according to cardiovascular risk and potentially identify a subgroup of patients who would most benefit from statin therapy.
The analysis included 950 MESA participants who had normal LDL cholesterol levels (less than 130 mg/dL) and elevated hsCRP (2 mg/L or more). All underwent two noncontrast CT scans to measure the calcium.
The authors noted that the average measured dose of radiation in a CAC scan was 0.89 mSv in MESA, while the average dose overall with modern technology ranges from 0.5 to 1.5 mSv.
Nearly half of the patients (47%) did not have any coronary calcium (a score of 0). Another 28% had scores of 1 to 100 and 25% had scores greater than 100.
Per 1,000 person-years, rates of coronary heart disease events increased from 0.8 for patients with a CAC score of 0 to 20.2 for patients with a score greater than 100. The patterns were similar for all cardiovascular events.
Through a median follow-up of 5.8 years, 74% of all coronary heart disease events and 60% of all cardiovascular events occurred in the patients with a CAC score greater than 100.
Applying the risk reduction accompanying rosuvastatin treatment observed in JUPITER (a 44% relative reduction in the risk of MI, stroke, and cardiovascular death), Blaha and colleagues calculated that the five-year number needed to treat (NNT) to prevent one coronary heart disease event was 549 for patients with a CAC score of 0, 94 for those with intermediate CAC scores, and 24 for those with scores greater than 1oo.
The NNTs for all cardiovascular events were 124, 54, and 19, respectively.
"These results have important implications for future guidelines and public health discussions aimed at improving the efficiency of statin use in primary prevention," according to the authors, who noted that studies have suggested that asymptomatic patients with a CAC score of 0 can be treated less aggressively with an emphasis on low-cost lifestyle interventions.
Blaha and colleagues acknowledged that a cost-benefit analysis is needed in patients with both low and high hsCRP to determine whether using CAC scores to guide statin treatment improves outcomes. They also acknowledged that CAC scoring has both advantages and disadvantages compared with hsCRP.
Advantages of CAC scoring include the fact that it is a direct measure of the burden of atherosclerosis, it has small variability on repeated testing, and it has consistent thresholds of risk in different populations. Thresholds for hsCRP vary by sex and ethnic origin.
Disadvantages include radiation exposure, a risk of incidental findings leading to further imaging, and a higher cost compared with hsCRP.
Still, CAC scanning can be performed for less than $100 in many centers, the researchers noted.
"Now that CAC scoring is so inexpensive, one can make the case of testing this in most patients at intermediate risk," commented Carl Lavie, MD, of the Ochsner Heart and Vascular Institute in New Orleans, in an email.
One obstacle to the wider adoption of CAC scoring for risk stratification "is that use of preventive measures such as statins, blood pressure control, and weight loss do not reduce the coronary calcium, and this is unsettling for many physicians and patients," said Howard Weintraub, MD, clinical director of the NYU Center for the Prevention of Cardiovascular Disease, in an email.
Some physicians want to see the value of the test proven in a randomized trial as well, although that has not stopped all physicians from incorporating it into their practices.
"Although definitive proof of treatment effects is scarce, CAC identifies high cardiovascular risk, and statin therapy is most effective in high-risk patients," Axel Schmermund, MD, and Thomas Voigtländer, MD, of Cardioangiologisches Centrum Bethanien in Frankfurt, wrote in an accompanying editorial.
"In our practice, we therefore focus on CAC ... for expanded risk stratification in asymptomatic patients."