Pediatric Reference Values and Z Score Equations for Left Ventricular Systolic Strain Measured by Two-Dimensional Speckle-Tracking Echocardiography

Background: In pediatric echocardiography, myocardial strain measurements are likely influenced by cardiac size and growth in healthy children. The application of this technique in clinical practice has been hampered by the lack of good normal reference values for the pediatric population. The aim of this study was to determine reference values and Z score equations for left ventricular systolic circumferential and longitudinal strain in a healthy pediatric population. Methods: Two hundred thirty-three healthy subjects 1 to 18 years of age were prospectively recruited. Left ventricular systolic longitudinal and circumferential strain measurements were recorded using two-dimensional speckle-tracking. Normalization for body size was performed using parametric nonlinear regression modeling. Several analyses were performed to detect potential residual associations with body size, residual heteroscedasticity, or departure from an adequate Z score distribution. Results: There were weak but statistically significant nonlinear associations between body size and most strain values. Body surface area was superior to adjust for body size compared with age, height, and weight. Most strain values displayed a second-order polynomial relationship with body surface area. Z score equations were computed with adequate normal distributions and without residual associations in relation to BSA for most strain parameters. Conclusions: There was a weak but significant influence of body size on most left ventricular circumferential and longitudinal systolic strain parameters used in pediatric echocardiography. Z scores are presented for strain measurements normalized to body surface area and adjusted for heteroscedasticity. The use of these normalized values may reduce the risk for misclassification caused by normal variation in myocardial strain values during growth.