Background: Elevated coronary artery calcium (CAC) is a marker for increase risk of coronary heart disease (CHD). Although most CHD events occur among individuals with advanced CAC, CHD can also occur in individuals with little or no calcified plaque. In this study, we sought to evaluate the characteristics associated with incident CHD events in the setting of minimal (score <or=10) or absent CAC (score of zero).
Methods: Asymptomatic participants in the MESA (N = 6,809) were followed for occurrence of all CHD events (including myocardial infarction, angina, resuscitated cardiac arrest, or CHD death) and hard CHD events (myocardial infarction or CHD death). Time to incident CHD was modeled using age-and gender-adjusted Cox regression.
Results: The final study population consisted of 3,923 MESA asymptomatic participants (mean age 58 +/- 9 years, 39% males) who had CAC scores of 0 to 10. Overall, no detectable CAC was seen in 3415 individuals, whereas 508 had CAC scores of 1 to 10. During follow-up (median 4.1 years), there were 16 incident hard events and 28 all CHD events in individuals with absent or minimal CAC. In age-, gender-, race-, and CHD risk factor-adjusted analysis, minimal CAC (1-10) was associated with an estimated 3-fold greater risk of a hard CHD event (HR 3.23, 95% CI 1.17-8.95) or of all CHD event (HR 3.66, 95% CI 1.71-7.85) compared to those with CAC = 0. Former smoking (HR 3.57, 95% CI 1.08-11.77), current smoking (HR 4.93, 95% CI 1.20-20.30), and diabetes (HR 3.09, 95% CI 1.07-8.93) were significant risk factors for events in those with CAC = 0.
Conclusion: Asymptomatic persons with absent or minimal CAC are at very low risk of future cardiovascular events. Individuals with minimal CAC (1-10) were significantly increased to 3-fold increased risk for incident CHD events relative to those with CAC scores of zero.