Background -Computed tomography (CT) allows estimation of coronary artery calcium (CAC) progression. We evaluated several progression algorithms in our unselected, population-based cohort for risk prediction of coronary and cardiovascular (CV) events.
Methods -In 3281 participants (45-74 years), free from CV disease until the 2nd visit, risk factors and CTs at baseline (b) and after a mean of 5.1 years (5y) were measured. Hard coronary and cardiovascular events as well as total CV events including revascularization were recorded during a follow-up time of 7.8±2.2 years after the 2nd CT. The added predictive value of ten CAC progression algorithms on top of risk factors including baseline CAC was evaluated using survival analysis, C-statistics, net reclassification improvement (NRI), and integrated discrimination index (IDI). A subgroup analysis of risk in CAC categories was performed.
Results -We observed 85 (2.6%) hard coronary, 161 (4.9%) hard CV and 241 (7.3%) total CV events. Absolute CAC progression was higher with vs. without subsequent coronary events [median 115 (Q1-Q3 23-360) vs. 8 (0-83), p<0.0001; similar for hard/total CV events]. Some progression algorithms added to predictive value of baseline CT and riskassessment in terms of C-statistic or IDI, especially for total CV events. However, CAC progression did not improve models including CAC5yand 5-year risk factors. An excellent prognosis was found for 921 participants with double zero CACb=CAC5y=0 [10-year coronary and hard/total CV risk: 1.4%, 2.0% and 2.8%], which was for participants with incident CAC 1.8%, 3.8% and 6.6%, respectively. When CACbprogressed from 1-399 to CAC5y?400, coronary and total CV risk were nearly twofold compared to subjects, who remained below CAC5y=400. Participants with CACb?400 had high rates of hard coronary and hard/total CV events [10-year risk: 12.0%, 13.5% and 30.9%, respectively].
Conclusions -CAC progression is associated with coronary and CV event rates, but adds only weakly to risk prediction. What counts is the most recent CAC value and risk factor assessment. Therefore, a repeat scan more than five years apart may be of additional value, except when a double zero CT scan is present or when the subjects are already at high risk.