Aortic root measurement on CT: linear dimensions, aortic root area and comparison with echocardiography. A retrospective cross sectional study.

Objective: We sought to assess the different CT aortic root measurements and determine their relationship to transthoracic echocardiography (TTE).

Methods: TTE and ECG-gated CT images were reviewed from 70 consecutive patients (mean age 54 ± 18 years; 67% male) with tricuspid aortic roots (trileaflet aortic valves) between Nov 2009 and Dec 2013. Three CT planes (coronal, short axis en face and three-chamber) were used for measurement of nine linear dimensions. TTE aortic root dimension was measured as per guidelines from the parasternal long axis view.

Results: All CT short axis measurements of the aortic root had excellent reproducibility (intraclass correlation coefficient, ICC 0.96-0.99), while coronal and three-chamber planes had lower reproducibility with ICC 0.90 (95% CI 0.84-0.94) and ICC 0.92 (0.87-0.95) respectively. CT coronal and short axis maximal dimensions were systematically larger than TTE (mean 2 mm larger, < 0.001), while CT cusp to commissure measurements were systematically smaller (CT RCC-comm mean 2 mm smaller than TTE, < 0.001). All CT short axis measurements had excellent correlation with aortic root area with CT short axis maximal dimension marginally better than the rest (Pearson's R 0.97).

Conclusion: Systematic differences exist between CT and TTE dependent on the CT plane of measurement. All CT short axis measurements of the aortic root had excellent reproducibility and correlation with aortic root area with maximal dimension appearing marginally better than the rest. Our findings highlight the importance of specifying the chosen plane of aortic root measurement on CT.

Advances In Knowledge: Systematic differences in aortic root dimension exist between TTE and the various CT measurement planes. CT coronal and short axis maximal dimensions were systematically larger than TTE, while CT cusp to commissure measurements were smaller. CT readers should indicate the plane of measurement and the specific linear dimension to avoid ambiguity in follow-up and comparison.