Calcium scans identify atherosclerosis not picked up by myocardial perfusion stress tests

Los Angeles, CA - Many patients with normal stress tests on myocardial perfusion single-photon emission computed tomography (MPS) may have calcium scores high enough to warrant medical treatment, a new study shows. [ 1 ] As such, the authors believe coronary artery calcium screening may be key to singling out patients for whom further imaging tests are warranted.

"Our findings demonstrate that a relatively high number of patients who had normal readings on their stress tests had a calcium score of greater than 100, a score that is accepted as implying the need for aggressive medical treatment," Dr Daniel Berman (Cedars-Sinai Medical Center, LA) commented in a press statement.

Berman et al's study appears in the August 18, 2004 issue of the Journal of the American College of Cardiology .

Stress tests and calcium scores

In their study, Berman et al followed 1195 patients half of whom were asymptomatic who had undergone stress testing and an electron-beam computed-tomography (EBCT) calcium scan within the course of six months. They report that while ischemia was absent on MPS in 1119 patients, 31% of these patients had CAC scores > 400 and 56% had CAC scores > 100. By contrast, among the 76 patients who demonstrated ischemia on stress testing, CAC scores were > 400 in 68% and > 100 in 88%. The presence of symptoms was a hallmark characteristic of patients with high calcium scores but normal MPS results.

"From these results, we concluded that patients with coronary calcium scores of less than 100 usually do not need to be referred for stress imaging testing," Berman said. By contrast, people with normal MPS scores may have underlying disease.

"Our study shows that patients who have normal imaging-stress-test results frequently have extensive atherosclerosis as revealed by coronary calcium scanning," Berman continued. "These findings imply a potential role for the coronary calcium scan, after an imaging-stress test among patients whose results are normal. These patients could then be identified as needing an aggressive treatment program of diet, exercise, and medications something that they often would not otherwise get based upon standard blood tests and the imaging-stress test results alone."

On the flip side, patients who have normal CAC scores likely do not need to be referred for MPS, they say.

Unmasking a subgroup of long-term risk patients?

Still uncertain is how best to deal with patients in the "gray zone" with CAC scores between 100 and 400. "Pending confirmation, our results suggest that within this range of CAC scores, clinical factors such as symptoms, gender, coronary risk factors, and stress ECG results may serve to impact substantially on the observed frequency of MPS ischemia."

Finally, say the authors, the wide range of CAC scores among patients with normal MPS scores underscores a key failing of all forms of stress testing: "They do not effectively screen for subclinical atherosclerosis," the authors observe. In a related manner, physicians do not yet know how to deal with patients with very high CAC scores but normal MPS results. "It is reasonable to hypothesize that such patients might be at low short-term risk but high long-term risk for cardiac events. If so, CAC could then be unmasking a subgroup of patients who would receive more aggressive antiatherosclerotic intervention than would have been indicated based on the results of MPS testing alone," they say, adding that the theory must be tested in future research.