Zero CAC Score Not 100% Reassuring in Those Presenting to ED With Chest Pain

October 16, 2009

October 16, 2009 (Baltimore, Maryland) — Patients presenting to the emergency department with chest pain should be treated aggressively regardless of any prior coronary artery calcium (CAC) score, a new analysis of the Multi-Ethnic Study of Atherosclerosis (MESA) demonstrates [1]. Confirming previous studies, however, patients with no prior evidence of coronary calcium who are asymptomatic have a low likelihood of developing coronary stenoses or a coronary event, the authors say.

Dr Boaz D Rosen (Johns Hopkins Medical Institution, Baltimore, MD) and colleagues show that in a subset of 175 patients who participated in MESA and subsequently underwent coronary angiography, primarily because of chest pain, seven (4%) had significant coronary obstruction despite having a zero CAC score at baseline. They report their findings in the October 2009 issue of the Journal of the American College of Cardiology: Cardiovascular Imaging.

Rosen et al also found that looking at calcium on a per-vessel level was less predictive of stenoses than looking at it on a per-patient basis, and they note that this was one of the first attempts to explore this issue.

Rosen told heartwire : "A previous finding of zero calcium score is not 100% reassuring. CAC scoring can miss soft plaques, which play an important role in [acute coronary syndrome] ACS. As a screening test, CAC is great, but it's not watertight for patients coming into the emergency room."

CAC scoring can miss soft plaques, which play an important role in ACS.

In an accompanying editorial [2], Dr Harvey S Hecht (Lenox Hill Heart and Vascular Institute, New York, NY) agrees: "The 96% negative predictive value in patients presenting with chest pain implies that a zero CAC does not provide sufficient reassurance. Therefore, CAC scanning is not an appropriate tool for chest-pain evaluation. A prior or recent zero CAC in a symptomatic patient must be followed by additional testing to rule out CAD with significant stenoses," he observes.

Rosen says that additional testing in patients presenting to the ED with chest pain should include CT angiography or other noninvasive evaluation, such as stress echo or nuclear testing, if the patient is deemed low risk. But if they are considered high risk, they should undergo coronary angiography, he stresses.

CAC Scanning Will Miss Soft Plaques

MESA enrolled 6814 asymptomatic patients, of whom over half, 3563, had zero CAC on CT at baseline.

This new analysis centers on the 175 individuals who had coronary angiograms in the first six years of the study, 80% of which were done because the patient had symptoms for clinical indications (angina, MI, or congestive heart failure), 5% as a direct result of the CT study, 5% for preoperative risk stratification, and 6% due to a positive stress test.

In the majority of cases (96%), the severity of CAC at baseline was directly related to the extent of obstructive coronary artery disease (CAD) on angiography, but in the remaining patients, there was significant stenoses despite a zero CAC score. Overall, there was a close association between baseline calcium mass score and the severity of stenosis in each of the coronary arteries (test for trend p<0.001).

In what Rosen said he considers a "secondary" part of the study, he and his colleagues also examined the relationship between the extent of CAC and the distribution and severity of coronary stenoses in individual coronary beds.

Although they found a significant relationship between the extent of calcification and mean degree of stenoses in individual coronary vessels, 16% of the coronary arteries with significant stenoses had no calcification at baseline.

"Although calcium is correlated to the amount of plaque, it is not necessarily correlated to the degree of stenosis of individual plaques," the researchers observe. "Similarly, the relationship between plaque calcification and the risk of plaque rupture is not well established. Plaques can rupture in the absence of calcium."

"Again, this highlights the importance of soft plaques that cannot be detected by assessing CAC score in patients who present with typical chest pain, ACS, etc," Rosen told heartwire .

They also found that for left main stenoses of 50% or greater, absence of calcium at baseline was noted in 35% of vessels. However, Rosen said that this finding is difficult to interpret, because "there are problems in measuring CAC in the left main artery. . . . It is a relatively short vessel, and there can be misregistration problems. I am not sure of the importance and implications of this finding."

CAC Screening Still a Good Test for Asymptomatic Patients

Rosen stresses that it is important to note that these analyses were done per-vessel and do not indicate the per-patient risk.

Therefore, aside from the mostly symptomatic patients assessed in this analysis, in asymptomatic patients, and on a per-patient level, coronary calcification remains an excellent predictor of future CAD events, and the calcium score "a useful surrogate of the total atherosclerotic burden in the coronary vessels."

Hecht agrees: "The purpose of CAC scanning has always been to detect the early subclinical stages of the disease, for which the specificity is virtually 100%, "and keep patients out of the cath lab by practicing aggressive prevention," he says. These findings "must be emphasized to hasten rather than further delay the acceptance of CAC screening."

A strong argument can now be made for requiring CAC before stress testing in asymptomatic patients, Hecht says. Also, less aggressive drug therapy is appropriate for zero-CAC patients, he believes, and "at the other end of the spectrum, CAC identifies the higher risk pool of patients in whom 95% to 96% of the events will emerge; it is this group that will benefit from highly targeted aggressive treatment," he concludes.

The study authors report no conflicts of interest. Hecht has served on the speakers' bureau for Philips Medical Systems.

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