Background NICE guidelines recommend CT calcium scoring as first line investigation for low risk chest pain followed by CT coronary angiography if the score is 1–400. The AHA and ESC guidelines however do not recommend the routine use of calcium scoring in chest pain evaluation. In our institution, most patients referred for CT investigation of chest pain or asymptomatic risk stratification have a CT calcium score (CAC) followed by a CT coronary angiogram (CTCA). The CONFIRM trial indicated a prevalence of 4.9% of coronary stenoses >50% in low risk symptomatic patients with a CAC score of zero.
Aims The aims of this study were: (1) to assess the diagnostic performance of CAC and (2) evaluate if there is any incremental benefit to routinely performing both CAC and CTCA, considering clinical yield and radiation exposure.
Methods The study period was 01/01/2012 to 31/12/2015. Inclusion criteria: (1) patients referred for evaluation of low to intermediate risk stable chest pain or (2) asymptomatic patients requiring cardiovascular risk stratification. Exclusion criteria: (1) CT scans performed to evaluate for anomalous coronaries, coronary bypass grafts or pulmonary venous anatomy pre ablation or (2) isolated CAC scoring performed without CTCA. The effective radiation dose was calculated for all scans in 2015.
Results 234 patients underwent a CAC score followed by a prospective ECG gated CTCA. Eighteen of these angiograms were significantly limited by motion or reconstruction artefact, rendering them nondiagnostic, and were excluded leaving 216 diagnostic scans in this study. The mean age was 49.5 years (range: 27–73 years). Forty seven percent (n = 101) were female. The mean CAC = 1 (range 0–1161). Seventy percent (n = 152) of patients had a CAC score = 0. Of the 152 patients with a CAC of 0, 18% (n = 28) were found to have mild atheroma on their CTCA. None had more significant disease. The diagnostic performance of CAC scoring over the four year period was calculated using CTCA as the standard. The negative predictive value of a CAC = 0 was 100%, while the positive predictive value of a CAC > 1 for greater than mild atheroma, was 70%. The sensitivity of CAC in our patient population was 100%, specificity 89%. There were no false negative results with a CAC = 0. The average total effective radiation dose of a combined CAC and CTCA was 3.3 mSv (range 1.6–6.5 mSv). The average effective radiation dose for a CAC score was 0.86 mSv (0.3–1.3 mSv) while the average for a CTCA was 2.2 mSv (0.8–4.8 mSv). On average, a CAC test accounts for 26% of the effective radiation exposure from the total investigation. There was a non linear relationship between CAC score and stenosis severity (Figure 1).
Conclusions CAC scoring demonstrated excellent negative predictive value for significant coronary artery disease in low to intermediate risk patients. A negative calcium score did not exclude mild atheroma, but also did not produce any false negatives for significant stenoses. CAC scoring requires considerable radiation exposure.
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