1. The left ventricular myocardial mass is a measurement that is easy to obtain by echocardiography. It is currently used for the definition of left ventricular hypertrophy, but cut-off values are often critical, since they depend on covariates of left ventricular myocardial mass such as sex, age, body surface area, physical training, blood pressure, etc. As it is very difficult in any laboratory to obtain a sufficient number of normal subjects for the establishment of left ventricular myocardial mass experimental distributions, we propose a non-linear model for the calculation of echocardiographic left ventricular myocardial mass distribution in normal subjects, from personal and literature data. Left ventricular myocardial mass probability density function was computed from the following two assumptions: the joint distribution of the internal and external left ventricular diameters is assumed to be bivariate normal, and the relation between left ventricular myocardial mass and ventricular diameters is given by the formula of Devereux & Reicheck (Devereux, R. B. & Reicheck, N. Circulation 1977; 55, 613-8).
2. The Gaussian assumption was tested by using skewness tests. The model was further developed for the myocardial mass index distribution. The calculated probability density functions were compared with experimental data and showed very good agreement. Furthermore, they were used to define cut-off values of left ventricular hypertrophy at selected false-positive ratios. Finally, since left ventricular myocardial mass may vary under normal conditions with co-variates, the model may provide co-variate-matched cut-off values for any, even small, series of non-diseased control subjects.