994-95 Variability Sources in Quantitative Coronary Arteriography

In a trial of progression/regression of coronary artery disease the results of quantitative coronary arteriography are affected by the following main factors: (i) the frame selected for analysis (FRAME), according to the general agreement, that the lesion should be measured at enddiastole. (ii) the frame rate (RATE), To obtain a truely enddiastolic image of a coronary lesion, a cine frame rate of 25 frames/sec is mandatory up to date. Newer digital equipped systems allow to use a frame rate of 12.5/sec, but there is concern, that one miss a truely representative enddiastolic image. (iii) the measurement variance (MEAS) obtained from repeated measurements. We analyzed the impact of these variability sources on the measurements in a study of 29 coronary lesions. The lesions were filmed at 25 and 12.5 frames/sec. The truely enddiastolic frame as well as the frame preceeding and following it was analyzed. Each frame was measured twice, using computer-assisted analysis of vessels. A nested multivariate analysis of variance was developed to quantify the effects of the independent variables RATE (12.5 instead of 25/sec), FRAME (enddiastole or a frame deviating from it) and MEAS (measuring the same frame twice) on the “outcome” in the sample the mean % diameter stenosis. The total variance in the sample by considering different stenosis (STEN; 15–75% diameter stenosis) was set to 100%. Results Multivariate analysis of variance shows the following influence of the various components on the size of % diameter stenosis: Independent variable STEN FRAME RATE MEAS Coefficient of variation 23.67 9.23 4.38 5.70 % contribution to total variance 100 15.20 3.40 5.90 Conclusions Frame selection is the major source of variability quantifying coronary lesions. Compared to the total variance the variance attributable to frame selection is nearly 3 times higher than the measurement variance and nearly 5 times higher than the rate attributable variance. Thus, one hasto take great care of selecting appropriate frames and may use the lower frame rate (12.5/sec) to reduce radiation exposure and facilitate digital image archiving.