Redefining aortic root assessment: standardising the maximum cusp-to-cusp diameter in multimodality imaging

Background Accurate aortic root measurement is critical, as surgical indication relies on precise diameter thresholds. Despite the recent 2024 ESC guidelines recommending the cusp-to-cusp method for assessing aortic root diameters by CCT/CMR, measuring the midpoint (MID) or the maximum (MAX) cusp-to-cusp diameter remains a subject of debate. Additionally, daily practice continues to be challenged as it remains unclear which correlates better with the transthoracic echocardiographic (TTE) measurement, the method with the strongest prognostic evidence. Purpose This study aims to determine the optimal measurement method for the aortic root by assessing reproducibility and correlation with TTE standards. Methods We included three populations: healthy volunteers, patients with bicuspid aortic valve (BAV) and hereditary thoracic aortic disease (HTAD). Patients were selected if they had undergone a TTE and either CCT or CMR within 12 months (six months for HTAD). Two cardiac imaging experts performed aortic root measurements, including cusp-to-commissure (CC), MID, and MAX diameters on CCT or CMR (Figure 1). TTE measurements were obtained in the parasternal long-axis view using the leading-edge to leading-edge method. Intra- and interobserver variability were assessed using the intraclass correlation coefficient (ICC), while agreement between TTE and CCT/CMR-derived diameters was evaluated with Lin’s coefficient. Results From 2022 to 2024, a total of 103 patients with clinical indications of both TTE and CCT/CMR were included (Table 1). The BAV cohort consisted of RCC-LCC fusion (83%, n=25) and RCC-NCC fusion (17%, n=5). The HTAD cohort included 26 Marfan (68%), 6 non-syndromic (16%), 4 with vascular Ehlers-Danlos (11%), and 2 with Loeys-Dietz (5%). The study covered a wide range of aortic root diameters, with most patients (63%, n=65) falling within 30–40 mm, while 21% (n=22) had diameters <30 mm and 16% (n=16) had diameters >40 mm. The MAX measurement consistently yielded larger diameters than MID, with absolute mean differences ranging from 2.7±1.2 mm (RCC-NCC) to 4.4±1.2 mm (RCC-LCC). Comparison of TTE diameters with distinct methods for aortic root measurements resulted in a stronger correlation with the MAX diameter: 0.70 for right coronary CC, 0.76 for MID, and 0.93 for MAX (all p<0.05) (Table 2). High reproducibility for both MID and MAX was confirmed by ICC: 0.97 vs 0.99 for interobserver (n=101, p<0.05), and 0.99 vs 1.00 for intraobserver agreement (n=20, p<0.05). Conclusions Our findings underscore that the MAX method not only yields the largest diameters, but also demonstrates a closer alignment with TTE measurements. Moreover, its high reproducibility is a key asset, ensuring reliable results in longitudinal follow-up studies and enabling consistent comparisons across different imaging modalities. Despite these insights, additional research is required to fully establish the prognostic value of using MAX aortic root diameters.