Doctors are already pretty good at predicting heart disease risk among healthy people, but a new study shows they could more accurately identify those at highest risk by adding a coronary artery calcium scan.
The test, done using a CT scan, assesses the amount of calcium people have in their blood vessels. That measure could reclassify about 25% of patients more accurately — into either a higher or lower risk category — when it comes to predicting their risk of having a heart attack over a 10-year period, report Dr. Joseph Yeboah, a cardiologist at Wake Forest Baptist Medical Center, and his colleagues in the Journal of the American Medical Association.
People who are found to be more vulnerable to heart disease may therefore decide to pursue more aggressive drug treatments, while those who are at lower risk may want to stick with diet and lifestyle changes to stay healthy.
Physicians currently use the Framingham risk score — which accounts for patients’ gender, age, cholesterol level, blood pressure and smoking status — to categorize people into one of three risk groups for heart attack: low (meaning they have a 5% chance of having a heart attack over 10 years), intermediate (5% to 20% risk of a heart attack) or high (more than a 20% risk). (You can get your Framingham score online.) These risk factors have been well studied since they were first identified in the 1960s, and people who are classified as low risk by their Framingham score are known to have fewer heart attacks and a smaller chance of dying early from heart disease than those categorized in the high-risk group.
But about 28 million Americans fall into the intermediate risk category — these patients pose a problem for heart doctors. Should they be treated aggressively with cholesterol-lowering or blood pressure-controlling drugs? Or would they be better off adjusting their diet and lifestyle and avoiding medications (and their side effects) altogether? A more accurate measure of their risk could help doctors decide on a better tailored treatment plan.
To find out whether adding other tests could improve doctors’ predictive ability beyond the Framingham score, Yeboah and his team conducted the first head-to-head study of a variety of additional factors. Starting with a group of 6,814 healthy middle-aged participants in six U.S. cities, the scientists calculated their Framingham score and then evaluated them on six other measures: coronary artery calcium; carotid artery thickness; the ratio of blood pressure between the lower leg and the arm; the elasticity of the blood vessels; an inflammatory marker called C-reactive protein; and family history of heart disease.
About 1,300 participants were determined to have intermediate heart risk, without diabetes, based on their Framingham risk score. After completing the six other tests, the participants were followed for an average 7.5 years. Over time, of all the additional tests, patients’ coronary artery calcium scores had the strongest independent ability to improve risk prediction for heart disease. “The question every clinician is asking is which one is best,” says Yeboah of the additional tests. “We put them head-to-head, compared all the top-tier markers our there, and the results showed that coronary calcium is better than all of the other markers at the moment.”
As we age, calcium tends to build up in our heart vessels, along with plaque from fat in our diet — all of which can stiffen the vessels and form fissures that turn into clots. When these clots rupture, they can block blood flow to the heart and trigger a heart attack. Using drugs to treat the high blood pressure that can cause tension in blood vessels, or to lower cholesterol and limit the build up of plaque, can lessen the chances of a heart attack for those most vulnerable to having them.
Detecting calcium in the heart, which can be an early sign of plaques, may be a helpful way to identify those at highest risk, as the current study suggests. But does that mean physicians should order a coronary calcium scan for all patients who fall into the intermediate Framingham risk group? That’s not clear: because the test is a CT scan, it involves a small dose of radiation and it’s costly. It’s too soon to say whether the benefit from the added information gleaned from the scan outweighs its potential risks — an increased risk of cancer down the road, for example.
That’s why heart guidelines leave the decision up to individual physicians; some doctors do order coronary calcium tests to inform their decision about treatments, while others do not. Data from studies like Yeboah’s, however, might solidify the role of coronary calcium testing in coming years. “We are not there yet, but this is a big step forward,” he says. “We found that yes, this is the best test available now but there is a lot of fine tuning we need to do if we want to apply it to the millions and millions of people who happen to be in the intermediate risk category.”