REGRESSION TOWARDS THE MEAN AND REPEATED ECHOCARDIOGRAPHIC MEASUREMENT OF LEFT-VENTRICULAR MASS

The selection of a group of patients based on a high value of a clinic al or biological parameter leads to the finding of a tendency to a red uction of this value when remeasured, known as ''regression towards th e mean''. The amplitude of this phenomenon is greater when the selecte d subjects are far from normal values and the intra-individual variabi lity of the parameter under consideration is very high. Measurement of left ventricular mass is very affected by this statistical phenomenon . The authors undertook a prospective study to analyse the components of variability of repeated echocardiographic measurements of left vent ricular mass and to quantify the expected effect of regression towards the mean in the follow-up of patients with left ventricular hypertrop hy. Twenty-five randomly chosen subjects underwent 2 echocardiographic examinations at 2 week intervals : at each visit, the patient had two recordings and each recording was measured twice by the same ''blinde d'' operator. Variance analysis showed intra-individual variability re presented 30% of total variability, comprising only 2% for the measure ments and 28% for the recordings and the visits. The importance of reg ression towards the mean was calculated with respect to the initial va lue of the left ventricular mass index: for example, when the left ven tricular mass index was 150 g/m(2), a spontaneous regression of 18 g/m (2) can be expected at the next measurement. This phenomenon should be taken into consideration in the interpretation of longitudinal echoca rdiographic studies.