Coronary Artery Aneurysm Measurement and Z Score Variability in Kawasaki Disease

Background: Coronary artery (CA) Z scores are commonly used for clinical decisions in Kawasaki disease, including treatment, anticoagulation, and duration and frequency of follow-up. The aim of this study was to evaluate CA measurement reproducibility, Z score calculation variability, and the impact of variability on management.

Methods: Twenty-one patients with Kawasaki disease with right CA (RCA) or left anterior descending CA (LAD) Z scores of 1.5 to 3 (group 1) were randomly selected, and all patients with Kawasaki disease with Z scores of 7 to 14 for either the RCA or LAD (n = 20; group 2) were included from March 2008 to May 2014. Two echocardiographers measured left main CA, LAD, and RCA dimensions. The inter- and intraobserver reliability of absolute measurements was calculated, and the CA Z scores derived from three commonly used formulas were compared.

Results: Median age at echocardiography was 1.2 years (range, 0.2-11.5 years), and 68% of subjects (n = 28) were male. Interobserver reliability was high for the LAD (intraclass correlation coefficient [ICC], 96.79%) and RCA (ICC, 93.31%) and lower for the left main CA (ICC, 73.54%). Intraobserver reliability was also high for the LAD and RCA (ICC, 99.08% and 97.74%) and lower for the left main CA (ICC, 80.88%). Calculated Z scores were similar among the three formulas for group 1 but varied markedly in group 2. Calculated Z scores using the same CA measurement in each of the three formulas resulted in different clinical management in up to seven of 21 group 1 patients (22%) and in up to 10 of 20 group 2 patients (50%).

Conclusions: Although CA measurements have high inter- and intraobserver agreement, CA Z scores vary dramatically on the basis of the Z score formula at larger CA dimensions. Discrepancies in CA Z score calculators may affect clinical decision making.