Objectives: In addition to the interest of mixing the sequence of echo-exam in a central blinded review, we studied the effect that might result from group-analysis of all echocardiograms simultaneously for each patient, with their sequence kept blind. A priori, this method of reading has the potential of decreasing measurement variability.
Methods: We included 630 echocardiograms from 210 hypertensive patients participating in a randomized clinical trial comparing two antihypertensive agents for regression of left ventricular (LV) hypertrophy. Three echocardiograms per patient [selection (4 weeks before; W-4), at inclusion (week 0; W0), and the end of treatment (week 52; W52)], were read twice, according to two methods, blind to centre, patient numbers and sequence of visits: (1) examination of individual serial echocardiograms, (2) examination of all-patient mixed echocardiograms. The first method was expected to increase the power of treatment comparison by reducing variability of measurements of left ventricular mass (LVM).
Results: Pooling echocardiograms of all patients reduces variability of LVM change under treatment: absolute LVM (W52 - W0) standard deviation was reduced by 22%. Nevertheless, despite a good between-methods agreement for LVM values at each visit (intra-class coefficient of correlation from 0.88 to 0.92), LVM change under treatment was reduced even more, by 41%. Thus, the slight decrease of variability induced by gathering the echocardiograms is associated with an even greater reduction of LVM change.
Conclusions: According to these findings, the 'full-blind' methodology for a central blinded review in clinical trials appears to produce the maximum power of the study with the lowest sample size.