Stratification beyond Framingham criteria is possible using coronary calcium score

November 11, 2008

Precisely defining intermediate cardiovascular-event risk using the Framingham Risk Score (FRS) is a challenge for clinicians. This is magnified when one considers that the number of patients who fall under the intermediate risk category outnumbers those considered low or high risk.

Precisely defining intermediate cardiovascular-event risk using the Framingham Risk Score (FRS) is a challenge for clinicians. This is magnified when one considers that the number of patients who fall under the intermediate risk category outnumbers those considered low or high risk.

In the group of patients with a 6- to 20-percent risk of an event over the next 10 years-as determined by using FRS-Allen Taylor, MD, advocates a more thorough family history and coronary artery calcium screening.

Twenty five to 50 percent of patients (depending on age) fall into this intermediate risk category by FRS. “This group doesn’t draw attention, but it has the highest population attributable risk,” he says.

Risk: a moving target
FRS is useful to stratify risk over 10 years but not over a lifetime, as “risk is a moving target,” says Dr. Taylor, professor of medicine at Walter Reed Army Medical Center, Washington, DC. Family history of premature cardiovascular disease is not included in FRS. As a binary measure, family history adds little to risk prediction but digging a little deeper can help further stratify risk, he believes.

For example, sibling history appears to be a robust marker of risk, as does the age and number of relatives with a history of cardiovascular disease. The more relatives affected, the higher the patient risk, especially if the relatives developed cardiovascular disease before age 60.

Noncontrast coronary computed tomography to obtain a coronary calcium score is strongly predictive of risk. Calcified atherosclerosis is highly heritable, says Dr. Taylor. It is present in 19.3 percent of patients with no family history of coronary disease but in 30.3 percent of those with both first- and second-degree relatives with a family history of coronary disease.

New ways to score coronary calcium, looking at spatial distribution of calcification in addition to the quantity of calcification, are improving the predictive accuracy of coronary calcium screening.

With a FRS greater than 5 percent, a coronary artery calcium score greater than 0 is associated with a nine-fold increased risk of coronary disease compared with a score of 0, notes Dr. Taylor. Further, the long-term prognosis of a person with a coronary artery calcium score of 0 is excellent; “it’s highly predictive of event-free survival,” he says. “It’s highly reassuring.”

Dr. Taylor notes that the Adult Treatment Panel III of the National Cholesterol Education Program endorsed coronary artery calcium screening to discriminate risk and guide intensification of therapy in intermediate-risk patients.

Recent data suggest that physicians are increasingly using coronary artery calcium screening to change therapeutic selection in patients at risk. Those patients undergoing coronary calcium scans have been found to receive aspirin and statins at three times the rate as those at-risk patients who do not undergo scans, he says.