Comparability of Z-score equations of cardiac structures in hypoplastic left heart complex

Abstract

Background: Hypoplastic left heart complex (HLHC) is characterized by a mitral valve or an aortic valve annular Z score < -2, antegrade flow in the ascending aorta, ductal dependency, coarctation or aortic arch hypoplasia, and absence of significant (sub)valvar stenosis. The Z scores of the mitral and aortic valve annuli are major determinants of HLHC. Therefore, the algorithm for Z-score calculation is essential for diagnosis. However, no single universal method of calculation is in use. In the scientific literature addressing HLHC, various Z-score calculation methods have been applied. The aim of this study was to evaluate Z scores derived from two-dimensional echocardiographic dimensions in patients with HLHC.

Methods: To compare the different published methods using two-dimensional echocardiographic measures for Z-score calculation, a cohort of 18 newborns diagnosed with HLHC was retrospectively evaluated. In addition, the methods to determine body surface area in newborns were evaluated.

Results: Three Z-score calculation methods were included and compared. Using the method of Daubeney et al. to calculate Z scores in our cohort illustrated a lack of correlation beyond a Z score < 0, compared with the methods of Zilberman et al. and Pettersen et al. Z scores calculated using Zilberman et al.'s and Pettersen et al.'s methods were fairly consistent. The equations used by Pettersen et al. are based on the largest population of neonates.

Conclusion: Although the different methods for calculating Z scores for mitral and aortic valve dimensions correspond fairly well in the normal range, Z scores < -2 diverge substantially. A useful scientific comparison of published data and outcomes of patients with HLHC remains elusive. The Z-score calculation algorithms used by Pettersen et al. appear to be the most appropriate for use in an evaluation of HLHC. Because these different methods can yield different values, reporting the method as well as the Z score is essential for an accurate diagnosis. Similarly, the method used to determine body surface area should be reported.

Keywords: AoV; Aortic valve; BSA; Body surface area; Borderline hypoplastic left heart syndrome; Coarctation; HLHC; HLHS; Hypoplastic left heart complex; Hypoplastic left heart syndrome; LV; Left ventricular; MV; Mitral valve; Z score.