ORLANDO — Coronary artery calcium identified young men at relatively high risk for a coronary heart disease event even when their Framingham risk score was low, in a study with more than 1,600 men.
The new findings “challenge the notion that a coronary artery calcium [CAC] score is only useful for people with an 'intermediate' Framingham risk score” of 10%–20%, Dr. Allen J. Taylor said at the annual scientific sessions of the American Heart Association. “It's rational to drop the threshold [for obtaining a CAC score] to a Framingham risk score of 5%” in younger men, those who are 40–50 years old, said Dr. Taylor, professor of medicine and chief of cardiology at Walter Reed Army Medical Center, Bethesda, Md.
Recommendations published last year by the American College of Cardiology and American Heart Association called for considering using CAC screening in people with a Framingham risk score (FRS) that shows a 10%–20% 10-year risk for a coronary disease event, but screening was not recommended in people with an FRS of less than 10% or more than 20% (J. Am. Coll. Cardiol. 2007;49:378–402). An FRS of less than 10% is generally considered to indicate a low risk for a coronary heart disease event to occur over the next 10 years, an FRS of 10%–20% indicates intermediate risk, and an FRS of more than 20% shows high risk.
“The only thing that makes these people [in the new study] low risk is that they're young. The Framingham risk score doesn't do it for people who are young because it only uses a 10-year horizon,” commented Dr. Philip Greenland, professor of medicine and dean for clinical and translational research at Northwestern University, Chicago.
Dr. Taylor's study used data collected in the Prospective Army Coronary Calcium Project, which began in 1998 and enrolled 2,000 healthy and asymptomatic men and women who were 40–50 years old at entry and underwent assessment with the FRS and CAC screening and have been followed for an average of almost 6 years. The new analysis focused primarily on the 1,640 men in the study, of whom 1,634 have full follow-up data. The average age of the men at enrollment was 43, and their average FRS was 4.6%. About a third of the men had an entry FRS of less than 3%, another third had an FRS of 3%–5%, and a third had an FRS of greater than 5%.
The CAC score was obtained using electron beam CT. Any score greater than zero was considered abnormal; 22% of the men had a CAC score above zero at baseline. The average CAC score was 20.
During follow-up that ranged from 1 to 8 years, the men had 14 “hard” coronary events, as well as eight cases of revascularization. The hard events included two instances of sudden cardiac death, six myocardial infarctions, and six hospitalizations for acute coronary syndrome.
The incidence of events was 4% in the 367 men with a positive CAC score at baseline, and 0.6% in the 1,267 men without discernable CAC at baseline. In an unadjusted hazard ratio analysis, men with a positive CAC score were about sixfold more likely to have a coronary event, compared with men without discernable CAC, Dr. Taylor said.
The incidence of events also was highest among the men with the highest FRS at baseline. Among those with an FRS of more than 5%, the event rate was 2.5%. The event rate was 1.1% in those with an FRS of 3%–5%, and 0.4% in those with an FRS of less than 3%.
Additional analysis showed the substantial impact of a positive CAC score on the rate of coronary events in people with a baseline FRS of 5% or greater. In this subgroup, those with coronary calcium had about a ninefold increased risk of an event, compared with those with an FRS of more than 5% but no coronary calcium, a statistically significant difference. In contrast, a positive CAC score had no significant effect on coronary risk in people with a starting FRS of 5% or less.
Men with a positive CAC score were about sixfold more likely to have a coronary event. DR. TAYLOR