body surface area (BSA) rather than to the square root of BSA. To the first point, we acknowledge the technical pitfalls that can result in erroneous measurement ...
Correspondence 449
Journal of the American Society of Echocardiography Volume 27 Number 4
Marleen Vonder, BSc Technical Medicine, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands Department of Radiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
have applied a variety of corrections,6 mostly involving correlations to exponential powers of BSA, including the square root suggested by Vonder et al. To evaluate the impact of correcting for the square root of BSA versus BSA itself, we generated a model to predict IVC diameter from BSA0.5 for comparison with the original model used to predict IVC diameter from BSA:
Tineke P. Willems, MD, PhD Department of Radiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
Model 1: IVC diameter ¼ 5:056 þ 6:541BSA; adjusted r 2 ¼ 0:517 Model 2: IVC diameter ¼ 2:077 þ 13:92BSA0:5 ; adjusted r 2 ¼ 0:534
Nynke J. Elzenga, MD, PhD Department of Pediatric Cardiology, Center for Congenital Heart Diseases, Beatrix Children’s Hospital, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
We then calculated the absolute value of observed minus expected IVC diameter for both models and compared these differences using a paired t test. Model 2 was statistically superior (P = .024), but the difference between observed and expected IVC diameters averaged 2.100 mm for model 1 and 2.029 mm for model 2. The improvement in estimation of IVC diameter was 7 hundredths of a mm and, although statistically significant, is of dubious clinical relevance. We believe, under the circumstances, that the conceptual and computational simplicity of the BSA model used in our report justifies its application.
Tjark Ebels, MD, PhD Department of Cardiothoracic Surgery, Center for Congenital Heart Diseases, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
Shelby Kutty, MD, FACC, FAHA, FASE David A. Danford, MD Division of Pediatric Cardiology, University of Nebraska Medical Center and Children’s Hospital and Medical Center, Omaha, Nebraska
Joost P. van Melle, MD, PhD Department of Cardiology, Center for Congenital Heart Diseases, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
REFERENCES
REFERENCES
1. Kutty S, Li L, Hasan R, Peng Q, Rangamani S, Danford DA. Systemic venous diameters, collapsibility indices, and right atrial measurements in normal pediatric subjects. J Am Soc Echocardiogr 2014;27:155-62. 2. Sluysmans T, Colan SD. Theoretical and empirical derivation of cardiovascular allometric relationships in children. J Appl Physiol 2005;99:445-57. http://dx.doi.org/10.1016/j.echo.2014.01.003
Authors’ Reply To the Editor: We thank the correspondents for their insightful letter highlighting the theoretical disadvantages of (1) image acquisition of the inferior vena cava (IVC) in its long axis and (2) normalization of vessel diameters to body surface area (BSA) rather than to the square root of BSA. To the first point, we acknowledge the technical pitfalls that can result in erroneous measurement of IVC diameter when displayed in the long axis. However, we chose this method in our investigation1 because it is the standard endorsed by the American Society of Echocardiography and the European Association of Echocardiography (now European Association of Cardiovascular Imaging) by which IVC measurements are made for the purpose of right atrial pressure estimation in adults2 and in children.3 We believe that sufficient care can (and must) be taken to record the IVC through its midline while displaying it longitudinally. In our judgment, the disadvantages of the method can be overcome, and the introduction of nonstandard methodology would have diminished comparability with foundational work in this field. Moreover, inconsistency in measurement methodology would result in inferior data quality. To the second point, we note that pediatric echocardiographers have long appreciated the nonlinearity of the relation between dimensions of cardiovascular structures and BSA.4,5 To account for variation in cardiac dimensions due to subject size, we and others
1. Kutty S, Li L, Hasan R, Peng Q, Rangamani S, Danford DA. Systemic venous diameters, collapsibility indices, and right atrial measurements in normal pediatric subjects. J Am Soc Echocardiogr 2014;27:155-62. 2. Rudski LG, Lai WW, Afilalo J, Hua L, Handschumacher MD, Chandrasekaran K, et al. Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. J Am Soc Echocardiogr 2010;23:685-713. 3. Lopez L, Colan SD, Frommelt PC, Ensing GJ, Kendall K, Younoszai AK, et al. Recommendations for quantification methods during the performance of a pediatric echocardiogram: a report from the Pediatric Measurements Writing Group of the American Society of Echocardiography Pediatric and Congenital Heart Disease Council. J Am Soc Echocardiogr 2010;23:465-95. 4. Sluysmans T, Colan SD. Theoretical and empirical derivation of cardiovascular allometric relationships in children. J Appl Physiol 2005;99:445-57. 5. Lipshultz SE, Miller TL. Establishing norms for echocardiographic measurements of cardiovascular structures and function in children. J Appl Physiol 2005;99:386-8. 6. Kutty S, Kaul S, Danford CJ, Danford DA. Main pulmonary artery dilation in association with congenital bicuspid aortic valve in the absence of pulmonary valve abnormality. Heart 2010;96:1756-61. http://dx.doi.org/10.1016/j.echo.2014.01.009
Quantification of Error in the Calculation of Z Scores in Neonates To the Editor: We agree with the conclusions in the article by den Dekker et al.1 regarding the caution with which Z scores should be interpreted, particularly in neonates. It is well established that widely differing results are generated by different Z-score algorithms, but it is also
