Ascending Aorta ULN Reference Comparison

This comparison demonstrates how different body size indexing methods produce different upper limit values, even when starting from similar populations. This is not an exhaustive review of all available aortic references, but rather an illustration of three distinct approaches to body size scaling.

How I Did This

Over the range of heights, a weight was calculated based on a BMI of 24; the DuBois equation was then used to calculate BSA. Since BSA depends on both height and weight, this allows the ASE's BSA-indexed reference values to be plotted across the height range alongside the other height-indexed references.

The JACC (CMR) area-for-height reference values were calculated and then converted to diameter.

Why These Differ

The three reference standards use different indexing methods to normalize ascending aortic dimensions for body size. This comparison intends to demonstrate the effect of the indexing method itself, independent of imaging modality differences. Although a bias may exist between CMR and echo measurements, the fact that these lines have different shapes and slopes is primarily due to how body size is accounted for in each reference.

Key Insights

• JACC (CMR): Uses area/height indexing with age dependency. Age is incorporated directly into the prediction equation. The area/height ratio has an allometric exponent of ~1.0, meaning aortic area scales linearly with height; aortic diameter therefore scales with the square root of height.
• NORRE (Echo): Height-indexed values (diameter/height ratio). Creates a straight line relationship - diameter increases proportionally with height. There is no age adjustment in these reference values.
• ASE (Echo): BSA-indexed using the DuBois formula (diameter/BSA ratio). There is no age adjustment in these reference values. This form of scaling results in a counterintuitive relationship where the ULN for females is greater than for males.

Clinical Takeaway

Different indexing methods can produce significantly different upper limit values, especially at the extremes of height. This underscores the importance of understanding which reference standard was used and how body size indexing affects the interpretation of measurements.

Citations

1. JACC (CMR): Tavolinejad, H., Beeche, C., Dib, M.-J., Pourmussa, B., Damrauer, S. M., DePaolo, J., Azzo, J. D., Salman, O., Duda, J., Gee, J., Kun, S., Witschey, W. R., & Chirinos, J. A. (2025). Ascending Aortic Dimensions and Body Size: Allometric Scaling, Normative Values, and Prognostic Performance. JACC: Cardiovascular Imaging. https://doi.org/10.1016/j.jcmg.2025.06.019
2. NORRE (Echo): Saura, D., Dulgheru, R., Caballero, L., Bernard, A., Kou, S., et al. (2017). Two-dimensional transthoracic echocardiographic normal reference ranges for proximal aorta dimensions: results from the EACVI NORRE study. European Heart Journal - Cardiovascular Imaging, 18(2), 167-179. https://doi.org/10.1093/ehjci/jew053
3. ASE (Echo): Lang, R. M., Badano, L. P., Mor-Avi, V., Afilalo, J., Armstrong, A., Ernande, L., Flachskampf, F. A., Foster, E., Goldstein, S. A., Kuznetsova, T., Lancellotti, P., Muraru, D., Picard, M. H., Rietzschel, E. R., Rudski, L., Spencer, K. T., Tsang, W., & Voigt, J. U. (2015). Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. Journal of the American Society of Echocardiography, 28(1), 1-39.e14. https://doi.org/10.1016/j.echo.2014.10.003