The Problem of Quantitative Coronary Angiography in Small Coronary Arteries: A Discussion with Intravascular Ultrasound as the Gold Standard

Purpose: Quantitative coronary angiography (QCA) is broadly used to measure reference diameter (RD) in percutaneous coronary intervention (PCI). One article showed that QCA was not correct in measuring small phantoms. The effect of this phenomenon in clinical status is not clear. We investigated whether or not QCA in small coronary arteries was accurate compared with intravascular ultrasound (IVUS). Methods: In 151 lesions (133 patients), IVUS and QCA were performed before PCI. RD was estimated by QCA and lumen diameter (LD) was measured by IVUS. The correlation between RD and LD were examined in two groups (group 1: RD < 2.8 mm, group 2: RD > = 2.8 mm). To check dispersion between RD and LD, the Bland-Altman plot and coefficient of variation (CV) were estimated. Results: LD strongly correlated with RD (r=0.67). This strong correlation was maintained in ordinary coronary arteries (group 2, r=0.60), but the correlation weakened in small coronary arteries (group 1, r=0.31). The limits of agreement in group 1 (-0.73 and 0.91) were larger than group 2 (-1.02 and 0.56). Additionally, CV in group 1 was grater than in group 2 (4.56 vs. 1.76). Conclusions: QCA for small coronary arteries showed a larger dispersion than QCA for ordinary vessels. Therefore, we should use IVUS to perform suitable dilatation in small coronary arteries.