Does coronary artery calcium scoring add to the predictive value of coronary computed tomography angiography for adverse cardiovascular events in low-risk chest pain patients?

Objectives: Coronary angiography calcium score (CACS) is included for patients who receive coronary computed tomography angiography (CTA) as part of diagnostic testing for low-risk chest pain. Both tests add radiation exposure, and it is unclear whether the combination provides more information than either test alone. The objective was to asses if CACS = 0 determines freedom from coronary artery disease (CAD) and whether the addition of CACS to coronary CT angiography provides additional risk stratification information or helps predict 30-day cardiovascular outcomes. Methods: This was a secondary analysis of a prospective cohort study at an urban university hospital emergency department (ED), of patients with symptoms suggestive of potential acute coronary syndrome (ACS) and low Thrombolysis in Myocardial Infarction (TIMI) risk scores who received coronary CTA. Data collected included demographics and medical history. The main outcome was CAD, defined as the presence of a maximal stenosis >50% on coronary CTA, stratified by CACS results. The secondary outcome was cardiovascular events including death, myocardial infarction, or revascularization at 30 days. Data were analyzed with standard descriptive techniques and relative risks (RR) with 95% confidence intervals (CIs). Results: A total of 1,049 patients were enrolled (median age = 48.1 years; interquartile range [IQR] = 42.4 to 53.3 years); 55% were female, and 63% were black or African American. Of these, 17 of 795 (2.1%) with CACS of 0 had CAD, 16 of 169 patients (9.5%) with CACS of 0.1 to 99 had CAD, 53.3% (32 of 60) with CACS between 100 and 399 had CAD, and 10 of 23 (43.5%) with CACS ≥ 400 had CAD. There was a higher likelihood of significant CAD with increased CACS. Patients who had a calcium score of 0 but still had CAD were more likely to be young (50 years old or less; RR = 1.73, 95% CI = 1.01 to 2.96). For the secondary outcome, there were 15 cardiovascular events within 30 days: one patient with CACS = 0 and no CAD (1 of 733; 0.1%), one patient with CACS > 0 and no CAD (1 of 182; 0.5%), four patients with CACS = 0 and CAD (4 of 17; 23.5%), and nine patients with CACS > 0 and CAD (9 of 58; 15.5%), with a net reclassification index of -0.001 (p = 0.32). Conclusions: In the study sample, elevated CACS was associated with a higher likelihood of underlying CAD on coronary CTA, but the addition of CACS to coronary CTA did not help predict 30-day cardiovascular events.