Novel Z Scores to Correct Biases Due to Ventricular Volume Indexation to Body Surface Area in Adolescents and Young Adults

Background: Reference values for cardiac magnetic resonance imaging (cMRI) in children and young adults are scarce. This leads to risk stratification of patients with congenital heart diseases to be based on volumes indexed to body surface area (BSA). We aimed to produce cMRI Z score equations for ventricular volumes in children and young adults and test whether indexing to BSA resulted in an incorrect assessment of ventricular dilatation according to sex, body composition and growth.

Methods: We retrospectively included 372 subjects aged <26 years with either normal hearts or conditions with no impact on ventricular volumes (reference group), and 205 subjects with repaired tetralogy of Fallot (TOF) aged <26 years. We generated Z score equations using multivariable regression modelling. Right ventricular dilatation was assessed using Z scores and was compared to indexation to BSA in TOF subjects.

Results: Ventricular volume Z scores were independent from age, sex and anthropometric measurements, while volumes indexed to BSA showed significant residual association with sex and body size. In TOF subjects, indexation overestimated dilatation in growing children and underestimated dilatation in females compared to males, and in overweight compared to lean subjects.

Conclusions: Indexed ventricular volumes measured with cMRI did not completely adjust for body size and resulted in a differential error in the assessment of ventricular dilatation according to sex and body size. Our proposed Z score equations solved this problem. Future studies should evaluate if ventricular volumes expressed as Z scores have a better prognostic value compared to volumes indexed to BSA.

Keywords: Cardiac magnetic resonance imaging; Indexation; Reference values; Ventricular volumes; Z scores.