ASSESSMENT OF TEMPORAL BIAS IN LONGITUDINAL MEASUREMENTS OF CAROTID INTIMAL-MEDIAL THICKNESS IN THE ASYMPTOMATIC CAROTID-ARTERY PROGRESSIONSTUDY (ACAPS)

A randomly selected subset of 100 pairs of baseline and 36-month follo w-up carotid B-mode ultrasound examinations from the 919 patients part icipating in the Asymptomatic Carotid Artery Progression Study (ACAPS) were subjected to a blinded rereading at the conclusion of the trial to assess temporal bias in the measurement of carotid artery intimal-m edial thickness (IMT), The original measurements of the primary outcom e variable and five secondary outcome variables at baseline and 36 mon ths, respectively, and the 3-year change in each of these variables, w ere compared with those obtained from the rereadings. For the primary outcome variable, the mean value of 12 IMT measurements obtained from predefined carotid segments, the mean difference (original - rereading ) and the 95% confidence interval which resulted from the rereadings w ere -0.005 (-0.033, 0.023) mm at baseline and -0.009 (-0.031, 0.013) m m at 36 months, The difference in the 3-year change was -0.004 (-0.038 , 0.028) mm, The 95% confidence interval for the mean difference betwe en the rereadings and the original readings for the baseline and the 3 6-month follow-up examinations included zero for all of the six outcom e variables as was also the case for the 3-year change in each variabl e. The magnitude of the mean differences for these 18 variables ranged from 0.004 to 0.034 mm, Intraclass correlation coefficients between t he original readings and rereadings ranged from 0.56 to 0.87 with the 3-year changes in outcome variables tending to have lower correlations and the 36-month examinations higher correlations, The carotid IMT me asurement process, when combined with uniform reader training, certifi cation and monitoring of reading performance throughout the course of the study, can avoid the temporal bias observed in other studies.