Title: Determinants of Coronary Calcium Conversion Among Patients With a Normal Coronary Calcium Scan: What Is the “Warranty Period” for Remaining Normal?
Topic: Noninvasive Cardiology
Date Posted: 5/20/2010
Author(s): Min JK, Lin FY, Gidseg DS, et al.
Citation: J Am Coll Cardiol 2010;55:1110-1117.
Clinical Trial: No
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JACC Article: Determinants of Coronary Calcium Conversion Among Patients With a Normal Coronary Calcium Scan: What is the “Warranty Period” for Remaining Normal?
Study Question: What are the frequency and clinical predictors of conversion from normal to abnormal coronary artery calcium (CAC) scans?
Methods: CAC scanning was performed annually for 5 years in 442 patients with baseline CAC = 0. CAC and clinical predictors were compared to a cohort of 621 subjects with baseline CAC >0. CAC was expressed in Hounsfield units (HU), and clinical predictors of age, diabetes, smoking, and others were tabulated.
Results: CAC progressed from an initial value of 0 in 106 of the 422 subjects (25.1%) with a mean time to conversion to abnormal of 4.1 ± 0.9 years. The number of subjects converting at years 1-5 was 2 (0.5%), 5 (1.2%), 24 (5.7%), 26 (6.2%), and 49 (11.6%). Age, smoking, diabetes, and hypertension were all significantly associated with the risk of conversion to CAC >0, but did not relate to the time at which conversion occurred. At the time of conversion, the average CAC score was 19 ± 19. Compared to subjects with baseline CAC >0, those with CAC = 0 were younger (48.8 ± 8.9 vs. 56.6 ± 8.6 years). The prevalence of hypertension, diabetes, smoking, and lipid disorder in those with CAC = 0 was 46%, 9.5%, 32%, and 66.4% compared to 56.5%, 16.3%, 36.4%, and 76.7% (p = NS for smoking, otherwise p ≤ 0.002). For individuals with a baseline CAC >0, 497 of the 621 (80%) had progression over a mean of 1.9 ± 1.1 years of follow-up with an average CAC increase of 45.5 ± 89.6 HU. The progression was statistically related to male gender, lipid status, smoking, and baseline CAC score, with only CAC score remaining independently predictive on multivariable analysis. Among propensity-matched cohorts, those with baseline CAC >0 had a higher frequency of progression than those with CAC = 0.
Conclusions: Progression of CAC from baseline score of 0 occurs at a low frequency within the first 4 years, and the presence of conversion is related to traditional risk factors. No traditional risk factor, however, predicts the timing with which conversion occurs.
Perspective: CAC scoring has been used as both a diagnostic and prognostic technique. Numerous studies have demonstrated the progressive likelihood of the presence and severity of coronary disease based on CAC and, furthermore, a higher likelihood of events and higher prevalence of positive cardiovascular stress testing with higher CAC. This study essentially asks the question: 'What is the warranty of a normal CAC?' This study, performed in a population of patients at intermediate risk of coronary disease but without clinical evidence of such at baseline scanning, suggests that the likelihood of progression from a CAC of 0 to advanced coronary calcium is negligible within 5 years and that the likelihood of progression to CAC >0 is low within the first 2-3 years after establishing a baseline. It appears that all patients in this study received the benefit of aggressive medical therapy for risk factor modification including uniform use of statins in those with elevated lipids. Not evaluated in this study was any link between conversion from a CAC of 0 and occurrence of events or change in symptomatic status. Assuming a link between CAC and cardiovascular events and/or need for further cardiovascular testing, it appears that serial determination of CAC is unwarranted at intervals <3-4 years in individuals with a score of 0 at baseline. William F. Armstrong, M.D., F.A.C.C.