Progression of CAC Score and Risk of Incident CVD.

OBJECTIVES: The authors sought to determine the relative contributions of baseline coronary artery calcification (CAC), follow-up CAC, and CAC progression on incident cardiovascular disease (CVD).

BACKGROUND: Repeat CAC scanning has been proposed as a method to track progression of total atherosclerotic burden. However, whether CAC progression is a useful predictor of future CVD events remains unclear.

METHODS: This was a prospective observational study of 5,933 participants free of CVD who underwent 2 examinations, including CAC scores, and subsequent CVD event assessment. CAC progression was calculated using the square root method. The primary outcome was total CVD events (CVD death, nonfatal myocardial infarction, nonfatal atherosclerotic stroke, coronary artery bypass surgery, percutaneous coronary intervention). Secondary outcomes included hard CVD events, total coronary heart disease (CHD) events, and hard CHD events.

RESULTS: CAC was detected at baseline in 2,870 individuals (48%). The average time between scans was 3.5 ± 2.0 years. After their second scan, 161 individuals experienced a total CVD event during a mean follow-up of 7.3 years. CAC progression was significantly associated with total CVD events (hazard ratio: 1.14, 95% confidence interval: 1.01 to 1.30 per interquartile range; p = 0.042) in the model including baseline CAC, but the contribution of CAC progression was small relative to baseline CAC (chi-square 4.16 vs. 65.92). Furthermore, CAC progression was not associated with total CVD events in the model including follow-up CAC instead of baseline CAC (hazard ratio: 1.05, 95% confidence interval: 0.92 to 1.21; p = 0.475). A model that included follow-up CAC alone performed as well as the model that included baseline CAC and CAC progression.

CONCLUSIONS: Although CAC progression was independently, but modestly, associated with CVD outcomes, this relationship was no longer significant when including follow-up CAC in the model. These findings imply that if serial CAC scanning is performed, the latest scan should be used for risk assessment, and in this context, CAC progression provides no additional prognostic information.