In some cases of congenital aortic anomalies or potentially undiagnosed tubular dilations, structural weakness of the ascending aorta predisposes to pathological dilation during prolonged periods of increased wall stress. Indeed, aortic rupture is an uncommon but important finding in all series of sudden cardiac death in young, ostensibly healthy, athletes, even in those undergoing preparticipation screening.1 Nevertheless, while aortic root values have been reported to be larger in pediatric athletes than in age-matched nonathletes,2 no normative values are available for aortic dimensions in healthy pediatric/adolescent athletes in the 4 main planes––aortic annulus, sinuses of Valsalva, sinotubular junction and ascending aorta––which is distinct from the situation in adult athletes.3 Clearly, having access to these data would aid clinicians in detecting pathologic abnormalities in young athletes.

Aortic root diameters are traditionally reported in absolute values; however, given the association between cardiac dimensions and anthropometric measures (ie, body surface area [BSA]), particularly in children, it has been proposed that allometric rather than linear scaling can provide cardiac measures that are body size-independent and would allow within- and between-subject comparisons along pubertal development.4 Of note, allometric scaling has been recently proposed for athletes across a relatively wide age range (12-35 years),5 but no specific subgroup analyses for pediatric/adolescent athletes were provided, and results were only available for the Valsalva sinus using M-mode ultrasonography. To address this issue, in the present study we report body size-independent aortic dimensions in pediatric/adolescent athletes.

We followed a cross-sectional, single-center study design. Participants were pediatric/adolescent athletes who underwent thorough preparticipation screening at the sports medicine center of the autonomous community of Madrid (Spain) during a recent 10-year period. Inclusion criteria were age 10 to 18 years and competing at national or international level. Exclusion criteria were having a bicuspid aortic valve, aortic dysplasia or prolapse, moderate or severe aortic regurgitation, high-gradient aortic stenosis, blood pressure> 95th percentile for the corresponding age and height, exercise-induced bronchoconstriction or hypertension, cardiomyopathy, left-right shunt, acute pericarditis, supra-aortic trunk disease, or second-degree atrioventricular block. Both athletes and their parents or legal representatives provided written consent and the study was approved by the local ethics committee.

We measured participants’ height and weight to the nearest 0.1cm and 0.1kg, respectively, and BSA. Echocardiographic evaluations were performed by the same sports cardiologist (AB, 30+ year experience) using a Siemens Sonoline G50 (Siemens Medical Solutions, Ann Arbor, United States) or a Mindray DC-70 (Shenzhen Mindray Bio-Medical Electronics, China) instrument with a 2 to 4MHz phase array transducer. Aortic diameters were measured in the aforementioned 4 planes in 2D parasternal long-axis view at end-diastole (using the average of 3 consecutive cycles) with the inner-inner convention, as previously performed in young adult elite athletes.3

We used Pearson's correlation analysis to explore the association between aortic dimensions and age and anthropometric measurements. Thereafter, we studied the allometric relationship between aortic dimensions and BSA by nonlinear regression using the Levenberg-Marquardt algorithm,6 also known as the ‘damped least squares method’, which is used to solve nonlinear least squares minimization. Minimization problems arise especially in least squares curve fitting, which is the process of constructing a curve or mathematical function that has the best fit to a series of data points. Thus, allometric-indexed aortic dimension=nonadjusted aortic dimension (mm)/(BSA, in m2)β, where β was determined with a confidence interval of 95%. Statistical analyses were performed with Stata 14.0 (StataCorp, College Stattion, United STates) with α=0.05.

Of the 637 athletes aged 10 to 18 years evaluated, 529 met the inclusion criteria (table 1). The athletes were engaged mostly in water polo (16%), swimming (16%), tennis (10%), synchronized swimming (6%), field hockey (13%), soccer (5%), and badminton (5%) competitions. Results showed that all 4 nonadjusted aortic dimensions positively and significantly correlated with age, height, weight, and BSA (all P<.001; table 2). However, significance for the correlation between each of the 4 dimensions and age was lost if the former were allometrically corrected for BSA (P> .3). All β-values for BSA were ∼0.5 [0.486-0.513], and for practicality we consistently used an age-independent β-value of 0.5 (which is actually equivalent to square root) for all sex-specific normative values of aortic root dimensions allometrically normalized by BSA (table 2).

A number of aortic abnormalities predisposing to pathological dilation during exercise can increase the risk of sudden cardiac death in young, apparently healthy, athletes.1 Accordingly, the assessment of aortic dimensions in the 4 planes is relevant in this population. However, in the absence of structural cardiopathies, the main determinants of aortic root and overall cardiac dimensions are sex, body size and age, which makes comparisons across children challenging.4 In this context, allometric scaling (but not linear correction) of BSA-adjusted cardiac measures is a valid procedure for obtaining body size- and age-independent values, at least in athletes aged 10 to 18 years.

There are some limitations in our study. We did not assess a control group of children not engaged in sports, and we studied athletes participating in sport events that might differ in cardiovascular demands (static or dynamic components) and thus, potentially, in aortic remodeling. Our use of the inner-inner method limits the comparability of our findings with respect to prior research using the standard leading edge-to-leading edge convention. By contrast, measurement of aortic diameters in the aforementioned 4 different planes should be considered a methodological strength of the study. Indeed, as we previously noted,3 performing only 1 to 2 measurements of the aortic root can result in over- or underestimation since aortic dilation distal to the supra-aortic ridge could be missed, with dilation potentially representing a risk factor for cardiovascular complications because of aortic dissection, especially in sports with higher hemodynamic loads.

We therefore propose normative values that might help clinicians to rapidly compare aortic root dimensions between children of different ages irrespective of their body size. This information should be useful in the early identification of aortic alterations that could limit sports participation, or at least justify close surveillance in pediatric/adolescent athletes.