Heart test gets a boost
Coronary artery calcium scanning -- a method that takes images of the coronaries and uses them to predict heart attack risk -- has soared in popularity over the last decade. But controversy has dogged the test for two reasons: a lack of scientific evidence that it can predict risk in people of all ethnicities and doubts about its cost-effectiveness.
One of those issues appears to be resolved. A study in last week’s New England Journal of Medicine shows the test is a strong predictor of heart attack risk in an ethnically and racially diverse group of people.
The study, funded by the National Institutes of Health, is the largest evaluation of coronary calcium testing to date, involving more than 6,700 people nationwide. The researchers showed that participants with a moderate amount of calcium buildup in their coronary arteries had a seven times greater risk of heart disease than people with no deposits. And people with a large buildup had a 10 times greater risk.
Previous studies have shown that accumulation of calcium in the arteries is a predictor of heart disease. But most of those studies involved small numbers of people who were mostly white.
“This study establishes that testing also predicts future events in other racial groups,” says Dr. Robert Detrano, professor of radiological sciences at UC Irvine and the study’s lead author. “I think this is a good test. If calcium is high, then we have a good reason to bring it down.”
The test uses CT scanning to measure the amount of calcium in the coronary arteries. It is noninvasive and takes only about 15 minutes. Patients are issued a score indicating the level of calcium buildup.
Many doctors are intrigued by the idea of adding a new tool to their arsenal for predicting heart attack risk -- because so far, assessing that risk is an inexact science at best. The standard method, called the Framingham risk score, is based on factors such as age, gender, cholesterol levels, blood pressure and smoking. This method is inexpensive and can predict the chances of a major coronary event within 10 years with 75% accuracy.
However, the Framingham risk score doesn’t identify everyone at risk. An estimated 250,000 people in the United States die each year from sudden cardiac death, some with no known heart disease risk factors. Some cardiologists believe that coronary artery calcium scoring could extend and refine assessments and identify people whom the Framingham test doesn’t capture.
But the issue of who should have the test has been controversial ever since it became commercially available in the 1990s. The test costs about $500. Insurance coverage varies widely, but the test is rarely reimbursed without prior authorization by the insurance company.
In a consensus statement released last year, two major medical groups -- the American College of Cardiology Foundation and the American Heart Assn. -- said the test was a reasonable option for patients with no heart disease symptoms who have an intermediate risk of having a heart attack as determined by the Framingham risk score. Someone with intermediate risk may have one or two risk factors for heart disease, such as high cholesterol and a family history of the disease.
However, the statement did not recommend the screening for people at low risk or for the general population.
Commenting on the new study, Dr. Allen Taylor, a cardiologist at Walter Reed Army Medical Center said, “This study is very consistent with what we know about the test. What is new in this paper is it extends the information to folks of varied ethnicities.”
Among the study’s participants, 38% were white, 27% black, 21% Hispanic and 11% Chinese. They ranged in age from 45 to 84, had no known cardiovascular disease and were followed for an average of 3.8 years.
Although previous research had shown that levels of detectable coronary calcification are generally lower in blacks, Hispanics and Chinese compared with whites, the study showed that the test is just as valuable for those groups as it is for whites. “Now we know that in minority groups, the test has at least equivalent value,” Detrano said. “There is no reason to deny the test based on ethnicity.”
Questions about the value of coronary artery calcium screening remain, however. For example, there are still no studies that prove the test is cost-effective -- that people, once they learn of their risk, change their behavior (eating better, exercising more, for example) or receive more aggressive medical treatment to lower their risk, thus preventing cases of heart disease.
Taylor said that cost-effectiveness will depend on whether doctors, based on the calcium score, advise their patients on how to lower their risk -- and whether patients adhere to the advice.
Some changes do seem to happen after patients get their scores. In a study presented in 2006 at a meeting of the American Heart Assn., Taylor reported that people who received coronary artery calcium testing were more likely to be prescribed aspirin and other medications to lower their risk.
“It’s clear the test is of additive value,” he says. “It’s now up to the healthcare system to figure out how to make the best use of that information.”
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