Because of limited storage capacity for digital images, angiographic laboratories without cinefilm are dependent on locally performed quantitative coronary angiography (QCA) in clinical studies. In the present study the intra- and interobserver variability, as well as variability between different laboratories and variability due to frame selection was analyzed. A total of 20 coronary lesions were studied in two different digital laboratories 12 +/- 8 days apart. Images were analyzed on-line and after being transferred to a Cardiac Work Station (CWS). There was no significant difference between the measurement situations. For minimal luminal diameter (MLD) precision (SD of signed errors) ranged from 0.12 mm to 0.20 mm, for reference diameter (RD) from 0.15 mm to 0.28 mm, and for percent diameter stenosis (DS) from 4.2% to 5.8%. Overall relative precision was obtained by normalizing the QCA parameters, and was 11.9% for MLD, 7.0% for RD and 8.5% for DS (p < 0.001, RD and DS compared to MLD). The overall variability in the interobserver and in the interlaboratory comparisons was 11.2% and 10.4%, respectively (n.s.) (n.s.). Thus the variability of QCA performed in cinefilmless, digital laboratories is small, and within a range making it an useful tool for clinical practice and group comparisons in clinical studies. However, the error range of QCA measurements must be taken into consideration when judging results from individual patients.
