Agreement between 4D transesophageal echocardiography and multi-detector computed tomography in measuring aortic root dimensions and coronary ostia heights

In this study, we discovered very strong correlations with good agreement between 4D TEE and MDCT-derived annular dimensions: annular area, annular perimeter, and area-derived diameter. Moreover, there were strong correlations and good agreement for LCA height, minimum STJ diameter, and minimum SoV diameters. However, we only detected moderate correlations and agreement with relatively large differences between the 95% LOA for RCA ostial height, maximum STJ diameter, and maximum SoV diameters.

Aortic annular dimensions

In this study, there were very strong correlations and agreement between 4D TEE and MDCT in the measured annular areas, perimeters, and their respective derived annular diameters. In general, the 4D TEE-derived annular dimensions were smaller than MDCT-derived diameters—it underestimated the annular area by 28.6 mm2 (5.7%), the annular perimeter by 3.2 mm (4%), the area-derived annular diameter by 0.8 mm (3.2%), and the perimeter-derived annular diameter by 1.0 mm (3.5%).

There were several comparisons between 4D TEE and MDCT in evaluating aortic root dimensions. Granata et al. was a prospective study that used the same 4D TEE software but on a smaller number of severe symptomatic AS patients (26 patients). They found a statistically significant strong correlation between the two methods in annular areas (r = 0.89, p < 0.0001), annular perimeters (r = 0.89, p < 0.0001), maximum annular diameters (r = 0.79, p < 0.001) and minimum annular diameters (r = 0.81, p < 0.001). The 4D TEE also underestimated MDCT measurements of the annular area by 65.3 mm2 (13.6%), annular perimeter by 4 mm (5.2%), maximum annular diameter by 1.2 mm (4.5%), and minimum annular diameter by 2.6 mm (11.3%) [10].

Four previous studies used older software versions. Calleja et al. was a study on 20 normal participants. It showed no significant difference between the two modalities in coronal, sagittal, and average annular dimensions, and the Bland–Altman plot showed good visual agreement [11]. Another retrospective analysis of 47 severe AS patients found significant correlations and good agreement in the area-derived annular diameters (r = 0.88, p < 0.001 and 95% LOA − 4.24 and 1.71 mm) and perimeter-derived annular diameters (r = 0.9, p < 0.001 and 95% LOA between − 3.94 and 1.73 mm) [4]. Similarly, using the same software, Kato et al. retrospectively analyzed the data of 43 severe AS patients undergoing TAVI. They demonstrated strong correlation and good agreement with narrow differences in the annular area (difference = − 6 mm2 (1.7%), r = 0.94, p < 0.001, 95% LOA between − 48.3 and 60.2 mm2) and the annular perimeter (difference = + 0.1 mm, r = 0.90, p < 0.001, 95% LOA between − 6.5 and 6.3 mm) [12]. Choi et al. found that the 4D TEE underestimated the annular area but with a significant correlation MDCT (difference = 34 mm2 (12%), r = 0.98, p = 0.018) [13].

Prihadi et al. used a different software to compare the two modalities in 150 patients with severe AS: the 4D TEE underestimated MDCT-annular dimensions, but both had strong correlation and good agreement in the annular area (difference = − 10.1 mm2 (2.2%), r = 0.91, p < 0.001, 95% LOA between − 78.5 and 58.4 mm2) and annular perimeter (difference = − 0.3 mm (0.4%), r = 0.83, p < 0.001, 95% LOA between − 8.5 and 8.2 mm) [7]. Khalique et al. reported similar findings with manual analysis of the 4D TEE datasets using a different machine: annular area difference = − 7.9 mm2 (2%) (r = 0.94, p < 0.001, 95% LOA between − 65 and 49.1 mm2), area-derived annular diameter difference = − 0.22 mm (1%), r = 0.94, p < 0.01) and annular perimeter difference = − 1 mm (1.3%), r = 0.93, p < 0.001, 95% LOA between − 6.0 and 4.0) [14].

Coronary ostial heights, STJ, and SoV dimensions

In our study, we found good correlations and good agreements with a relatively small difference for the LCA ostial height (r = 0.84, p < 0.01, CCC = 0.83, 95% LOA between − 2.29 and 0.67 mm), minimum STJ diameter (r = 0.793, p < 0.01, CCC = 0.723, 95% LOA between − 9.2 and 7.49 mm) and minimum SoV diameters (r = 0.779, p < 0.01, CCC = 0.687, 95% LOA between − 10.2 and 6.6 mm). But the correlations and agreement were moderate with relatively large differences for RCA ostial height (r = 0.68, p < 0.01, CCC = 0.67, 95% LOA between − 3.25 and 4.15 mm), maximum STJ diameter (r = 0.658, p < 0.01, CCC = 0.594, 95% LOA between − 12.02 and 12 mm) and maximum SoV diameters (r = 0.667, p < 0.01, CCC = 0.537, 95% LOA between − 14.7 and 14.5 mm). We could not come up with a plausible explanation for the moderate correlation in the RCA height versus the good correlation in LCA height, and none of the previous studies reported results on this point: they only published data on the LCA or no data on coronary ostial heights at all.

Fewer studies investigated the correlation between 4D TEE-derived and MDCT-derived coronary arteries’ ostial heights, SoV, and STJ dimensions.

Granata et al. also found a statistically significant moderate positive correlation for RCA ostial height (r = 0.53, p = 0.007) but a weak non-significant correlation for LCA ostial height (r = 0.33, p = 0.1) [10]. Tamborini et al. also reported a strong correlation (r = 0.83, p = 0.01), and a good agreement was good in the LCA height, and the difference was small and non-significant (0.4 mm) [15].

In Prihadi et al. study, 4D TEE underestimated the mean STJ diameter (− 1.4 mm) with good correlation and agreement (r = 0.73, p < 0.001, 95% LOA between − 4.8 and 4.0 mm), and the mean SoV diameter (− 0.7 mm) with good correlation and agreement (r = 0.87, p < 0.001, 95% LOA between − 4.2 and 2.8 mm) [7]. Similarly, Choi et al. study showed that 4D TEE underestimated both maximum STJ diameter (2.69 ± 0.26 vs. 3.19 ± 0.21 cm, r = 0.775, p = 0.042) and maximum SoV diameter (3.16 ± 0.32 vs. 3.92 ± 0.46 cm, r = 0.993, p = 0.007) with significant good correlation [13].

In contrast, Calleja et al. revealed a significant difference in coronary ostial heights measured by 4D TEE and MDCT. The 4D TEE measurements were smaller for the left (11.3 vs. 12.9 mm, p = 0.03) and right (11.6 vs. 13.1 mm, p = 0.001) coronary ostial heights. The mean 4D TEE-derived STJ and SoV diameters were also smaller by 1.4 mm (p < 0.01) and 2.8 mm (p < 0.01), respectively. However, these findings should be interpreted cautiously because the 4D TEE population differed from the MDCT population in this study [11].

Automated analysis of both 4D TEE and CT datasets and their validation is currently an area of active interest in medical research: due to the increased availability of transcatheter structural interventions, especially TAVR, and the increased complexity of aortic root surgeries. Currently, MDCT evaluation of the aortic root is the gold standard despite the drawbacks of ionizing radiation and the use of iodinated contrast, which can be troublesome in patients with renal impairment [1]. The improvements in hardware and software, especially artificial intelligence, made 4D TEE a theoretically viable alternative to MDCT.

To our knowledge, this study is the first to compare 4D TEE and MDCT-derived aortic root dimensions in various aortic root and valve pathologies, including normal root and valve, severe AS, and dilated aortic root. To date, only a few studies have compared semi-automated 4D TEE with MDCT in evaluating aortic root dimensions—they all focused on aortic annular dimensions and were only done in patients with severe AS in preparation for TAVR procedures.

Study limitations

This study has some limitations. First, it is a single-center study, and its results should be interpreted with caution and further validated in larger multicenter trials. Also, this study did not measure clinical outcomes based on decisions using data obtained from 4D TEE or MDCT. This question can be investigated further through clinical outcome studies. Finally, the limited ability of TEE to detect and quantify calcification can impede assessment in severely calcific aortic roots and valves.

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