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, professor of medicine and chief of cardiology at Walter Reed Army Medical Center in Washington, said at the annual scientific sessions of the American Heart Association. “It's rational to drop the threshold [for a CAC score] to a Framingham risk score of 5%” in younger men, those aged 40 to 50 years.
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 those 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% generally indicates a low risk for a coronary heart disease event 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 [making those in the new study] low risk is that they're young. The FRS doesn't do it for people who are young because it only uses a 10-year horizon,” said 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. Average age at enrollment was 43, and average FRS was 4.6%. About a third had an entry FRS of less than 3%, a third had an FRS of 3%–5%, and a third had an FRS 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 was 20.
During follow-up that ranged from 1 to 8 years, the men had 14 “hard” coronary events, as well as 8 cases of revascularization. The incidence of events was 4% in the 367 men with a positive CAC score at baseline, and 0.6% in 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. The incidence of events also was highest among the men with the largest FRS at baseline.
Additional analysis showed the impact of a positive CAC score on the rate of coronary events in people with a baseline FRS of 5% or greater. 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 calcium, a significant difference. A positive CAC score had no significant effect on coronary risk in those with a starting FRS of 5% or less.
Another analysis highlighted the prognostic role of the CAC score in this group. Even when they were controlled for baseline FRS, men with a CAC score of 10–44 had an almost 6-fold increased risk for an event, compared with those with no coronary calcium, and men with a CAC score of more than 44 had a 10-fold increased risk, compared with those with no coronary calcium. Both of these hazard ratios were statistically significant. A CAC score of less than 10 had no significant impact on the event rate. “The results show the independent value of CAC screening in young, middle-aged men,” Dr. Taylor said.
'The results show the independent value of CAC screening in young, middle-aged men.' DR. TAYLOR