Divergent Aortic Root Cusp-to-Cusp Measurement Techniques on CMR: Geometric Implications and Threshold Reclassification

Objective To evaluate discrepancies between current European guidelines (ESC vs. EACTS) regarding aortic root cusp-to-cusp measurements and assess their impact on risk stratification for prophylactic root replacement. Methods A retrospective analysis was performed on a relative young cohort of 50 patients (mean age 42 years) who underwent non-contrast 3D cardiovascular magnetic resonance (CMR) imaging. We compared the widest-to-widest cusp measurements and the middle cusp-to-cusp measurements with each other and against a traced aortic root perimeter. Results The widest cusp-to-cusp measurement yielded systematically higher values compared to the middle measurement, showing a significant mean difference of 3.60 mm (p < 0.001). The middle measurement demonstrated better statistical agreement with the traced aortic root perimeter, achieving a Lin’s Concordance Correlation Coefficient (CCC) of 0.98 and a Mean Absolute Error (MAE) of 3.96 mm. Conversely, widest cusp-to-cusp measurements exhibited substantially lower agreement (CCC 0.80) and significantly higher error rates (MAE 16.88mm), consistently overestimating the perimeter. This led to the upward reclassification of 10.0% (5/50) and 16.0% (8/50) of patients across the 40 mm and 45 mm guideline thresholds, respectively. Conclusions Cusp-to-cusp measurement techniques recommended by ESC and EACTS produce systematically divergent aortic root dimensions, resulting in significant patient reclassification across clinical thresholds. Although the middle measurement aligns more closely with the traced anatomical perimeter, the principal finding of this study is that guideline choice fundamentally alters patient categorization. Standardization of aortic root measurement conventions is essential to ensure consistent international care, improve research comparability, and reconcile historical risk thresholds with modern 3D imaging.