Abstract 9439: Incidence of New Coronary Calcification: What is the Warranty Period of CAC = 0 in the Multi-Ethnic Study of Atherosclerosis?

Abstract

Background: While CAC=0 is associated with excellent prognosis, progression to CAC>0 has been shown to confer increased risk. The time interval at which a repeat CAC scan would be reasonable - the “warranty period” of CAC=0 - is currently poorly defined. Methods: We studied 3116 participants from the Multi-Ethnic Study of Atherosclerosis (MESA) with baseline CAC=0 and at least 1 follow-up CAC scan per MESA protocol (up to 10 years after baseline). Cumulative incidence of incident CAC was calculated yearly. Cumulative survival fee of CAC was calculated using Kaplan-Meier statistics and additionally modeled using a parametric survival model with Weibull distribution. The warranty period of CAC=0 was defined distribution as the time needed for 15%, 20%, or 25% (number needed to scan [NNS] 6, 5, or 4) to progress to detectable CAC. Results: The mean age of the subjects was 58 ± 9 years with 63% women and mean FRS of 8 ± 6%. Cumulative prevalence of CAC>0 increased with time, from 11% at 2 years to nearly 50% at 10 years. The cumulative incidence rate of CAC>0 was non-linear, increasing from approximately 2.5 per 100 person-years at 2 years to 5-6 per 100 person-years from years 4 to 10. The table shows the estimated warranty period of CAC=0 by gender and baseline FRS CHD risk. Among men, using an acceptable detection rate of 25% (NNS=4 to detect CAC>0), the estimated warranty period of a low, intermediate, and high risk man was 6, 5, and 3 years. For women, the equivalent warranty period was 7, 5, and 4 years. In general, rescanning at 5 years will enable selection of 50% of the individuals with baseline CAC=0 who will go on to have CHD events following their repeat scan over 10-year follow-up. Conclusions: Although limited by lack of yearly CAC scanning, modeling in MESA allows estimation of the warranty period of CAC=0. A general rule would be to rescan low risk CAC=0 patients at 6-7 years and intermediate risk at 4-5 years, although exact warranty periods vary by gender and desired yield of repeat testing.