Estimates of interventricular septum thickness are markedly affected by the method used.

Modern echocardiographic techniques allow precise measurements of interventricular septum thickness by two-dimensional echocardiography (2DE) and M-mode echocardiography. The advantage of 2DE is the more accurate estimate in cases in which the shape of the septum differs from normal. However, the usefulness of measurements by 2DE is limited due to the lack of reference values. We measured maximal septum thickness by 2DE in 168 healthy subjects aged 2 to 27 years and compared the results to those obtained by M-mode. In agreement analysis the bias +/- 2 SD between 2DE and M-mode was 0.8 +/- 1.7 mm (p <0.001). Maximal septum thickness exceeded the upper normal limit (+2 SD) of the largest pediatric reference data in 14 (8%) of the healthy subjects studied. Interventricular septum thickness is greater when measured by 2DE than by M-mode. Previous M-mode reference values should be used with caution; preferably, reference data based on 2DE should be used.