Automated and manual measurements of the aortic annulus with ECG-gated cardiac CTA prior to TAVR

Guez D, Boroumand G, Ruggiero NJ, Mehrotra P, Halpern EJ.

* This article originally appeared in the January 2017 edition of Academic Radiology.

Rationale and Objectives
Multimodality evaluation of the aortic annulus is generally advocated to plan for transcatheter aortic valve replacement (TAVR). We compared aortic annular measurements by cardiac computed tomography angiography (cCTA) to three-dimensional transesophageal echocardiography (3D-TEE), and also evaluated the use of semi-automated software for cCTA annular measurements.

Materials and Methods
A retrospective cohort of 74 patients underwent 3D-TEE and electrocardiogram-gated cCTA of the heart within 30 days for TAVR planning. 3D-TEE measurements were obtained during mid-systole; cCTA measurements were obtained during latesystole (40% of R-R interval) and mid-diastole (80% of R-R interval). Annular area was measured independently by manual planimetry and with semi-automated software.

Results
cCTA measurements in systole and diastole were highly correlated for short-axis diameter (r = 0.91), long-axis diameter (r = 0.92), and annular area (r = 0.96), although systolic measurements were significantly larger (P < 0.001), most notably for the short-axis diameter. Good correlation was observed between 3D-TEE and cCTA for short-axis diameter (r = 0.84–0.90), long-axis diameter (r = 0.77– 0.79), and annular area (r = 0.89–0.90). As compared to 3D-TEE, annular area is overmeasured by 28 mm² on systolic phase cCTA (P < 0.008), but nearly identical with 3D-TEE on diastolic phase cCTA. Semi-automated and manual cCTA annulus measurements were highly correlated in systole (r = 0.94) and diastole (r = 0.93), although the semi-automated annular area measured 11–30 mm² greater than manual planimetry. Of note, the 95% limits of agreement in our Bland-Altman analysis suggest that the variability in annular area estimates for individual patients between cCTA and 3D-TEE (−100.9 to 99.6 mm²), as well as the variability between manual and automated measurements with cCTA (−105.9 to 45.2 mm²), may be sufficient to alter size selection for an aortic prosthesis.

Conclusions
Although all cCTA measurements are highly correlated with measurements by 3D-TEE, diastolic phase cCTA measurements tend to be closer to standard mid-systolic 3D-TEE measurements. Semi-automated measurement of the aortic annulus with cCTA is highly correlated with manual planimetry. Nonetheless, annular contours derived by semi-automated software should be visually inspected, as the variability in area estimates for individual cases between manual and automated measurements may alter the sizing of an aortic prosthesis.

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