Marfan Syndrome Aortic Root Dimensions

Establishing whether the aortic root is enlarged requires three things. The first is what the "normal" aortic root dimension is, the second is how much above this should be considered enlarged, and the third is an accurate measurement of the patient's aortic root size. The reference for the "normal" root dimension requires data and proper application or use of that data. These data need to include important factors that may limit the use of the refence such as gender, race, or others that might systematically affect the results. How much above the threshold is used for defining enlargement is arbitrary but contributes to the sensitivity and specificity of this as a diagnostic criterion. This definition is independent of the degree of enlargement that needs medical intervention. The aortic root measurement for the patient needs to be carefully done using a technique that matches the technique used to generate the reference value.

The diagnostic criteria described by DePaepe and colleagues includes several nomograms for evaluating aortic root dimensions that were reproduced from a publication by Dr. Roman and colleagues1. These normalize the aortic dimension to the body surface area. The aortic dimension is measured at the sinuses of Valsalva by cross-sectional 2-dimensional surface echocardiography from the parasternal long-axis view. No description of the method to calculate the body surface area is given, so for the Automated Marfan Syndrome Checklist the Mosteller2 formula is used:

BSA(m2) = ([Height(cm) x Weight(kg)] / 3600)1/2

The nomograms define the 95% confidence intervals. This is +1.96 times the standard error (SEE or standard error of the estimate on the graphs). Values above the top end of this interval are considered "enlarged." A re-creation of these nomograms are reproduced below for easy reference.

The publication by Roman and colleagues1 states that the infant and child nomogram was based on data from from 52 infants and children from ages 1 month to 15 years and adult nomograms were based on data from 135 adults from 20 to 74 years of age. This leaves patients in the 15 to 20 year old range as not being represented in either curve. For the calculations used for the Automated Marfan Syndrome Checklist ages under 17.5 years are considered infants or children and 17.5 years and older are considered as adults. Additionally, no description of race is included so these same nomograms are used for all individuals.

Aortic root dimension nomogram for children Aortic root dimension nomogram for adutls less than 40 Aortic root dimension nomogram for adutls greater than 40

In each of these graphs the central diagonal line represents the expected aortic root diameter and is flanked by lines representing the 95% confidence intervals. Clicking on the graphs will display a larger version.

More recently Dr. Pettersen and colleagues published data from a much larger cohort of infants to adolescents and a number of echocardiographic measurements3. These data are from 782 patients age 1 day to 18 years, a little better than the 52 from.

The Pettersen3 data use the Dubois body surface area formula for normalization (example BSA calculator page).

BSA(m2) = 0.20247 x ([Height (cm)] / 100)0.725 x [Weight (kg)]0.425

The aortic root measurements are made at the sinuses of valsalva hinge points from the parasternal long axis view at their maximum systolic dimention. The article provides a table with coefficients and a formula for calculating Z-scores. The coefficients for the sinuses of Valsalva measurements are -0.5 for the intercept (β0), 2.537 for BSA (β1), -1.707 for BSA2 (β2), 0.420 for BSA3 (β3), and 0.012 for the mean square error (MSE), with an R2 of 0.916.

1. Roman MJ, Devereux RB, Kramer-Fox R, O'Loughlin J: Two-dimensional echocardiographic arotic root dimensions in normal children and adults. Am J Cardiol 1989 Sept 1;64:507-512
2. Mosteller RD: Simplified Calculation of Body Surface Area. N Engl J Med 1987 Oct 22;317(17):1098 (letter)
3. Pettersen MD, Wei Du, Skeens ME, Humes RA: Regression Equations for Calculation of Z Scores of Cardiac Structures in a Large Cohort of Healthy Infants, Children, and Adolescents: An Echocardiographic Study. J Am Soc Echocardiogr. 2008 Aug;21(8):922-34

This description is a part of the Automated Marfan Syndrome Checklist.