Three-dimensional echocardiography vs. computed tomography for transcatheter aortic valve replacement sizing

Dear Professor Maurer It’s not what you use, it’s how you use it that matters! We read with interest the paper by Vequerizo et al (1), which compares annulus measurements, obtained by 3D transesophageal echocardiography (TEE) and multi-slice computed tomography (MSCT) in a single center cohort of just over 50 patients. Although moderate to high correlation was noted between the perimeter measured by 3D TEE and MSCT, 3D TEE yielded significantly smaller measurements. The authors consider MSCT as the gold standard and conclude that 3D TEE should not be used routinely for valve sizing except when MSCT is not available or is contraindicated. Firstly, although we accept that the MSCT has been more frequently used for aortic valve annulus measurement in TAVI in recent years, we would caution calling it the “gold standard”. In fact, Tsang et al showed that in an in vitro model, cardiac magnetic resonance (CMR) produces the most accurate measurements. In the in vivo model both MSCT and 3D echocardiography were reasonable alternatives (2) with the caveat that MSCT overestimated the CMR measurement. Secondly, whilst research in TAVI valve sizing has been mainly focused on the comparison of the tests and their diagnostic accuracy, the impact of different modalities on clinical outcomes has not been extensively investigated and was not looked at in this study. Whilst conducting a randomized trial for a head to head comparison of the impact of different imaging modalities used in annulus sizing on clinical outcome does not seem realistic, observational studies from high volume centers could be valuable. At King’s College Hospital, London, UK where a total of 429 TAVIs have been performed since the start of the program, TEE has been successfully used for valve sizing in all patients except four cases. In a cohort of 230 patients who have undergone TAVI at this center between January 2013 to December 2015, reflecting a more contemporary practice, we observed only eight patients with moderate AR (3.5%) and no severe AR at the end of procedure assessed by intra-procedure TEE. The 30-day mortality in this group was 2.2 % (5 in 230) and one-year mortality was 9.5% in applicable group (12/126). These outcomes compare extremely favorable with any series where MSCT was used for valve sizing. At Columbia University, New York, US where a total of >1500 TAVIs have been performed since the start of the program, 3D TEE sizing of the annulus began in February 2014 and routine MSCT sizing began in October, 2014. In an early retrospective study prior to MSCT annular sizing, 150 patients with 2D TEE (sagittal diameter) sizing only and 126 patients with both 2D and 3D (area and perimeter) TEE sizing were studied. In this series of SAPIEN and SAPIEN XT valve implants, 50% had no AR, 28% had trace, 15% had mild and 7% had moderate AR. There were no patients with severe AR. Although these rates were not significantly different between the 2D and 3D sizing groups (p = 0.29) importantly the post-dilatation rates were dramatically reduced (47% vs 27%, p = 0.027) suggesting that 3D TEE sizing significantly improved procedural outcomes. In a more contemporary study of the early SAPIEN 3 experience, 63 patients had sizing by both MSCT and 3D TEE with no AR in 32 (50.8%), trace AR in 21 (33.3%), mild AR in 10 (15.9%) and no patient with moderate or severe AR. In this series, AR severity was significantly predicted by 3D TEE %oversizing (p = 0.034) but not by MSCT %oversizing (p = 0.07). Based on the limitations of the study by Vequerizo, which have been appropriately addressed in the paper, and also the current literature supporting the favorable accuracy of 3D TEE in annulus sizing (3-5), we disagree with the conclusion that has been drawn from this small study. We think the focus should not be on what 3D modality to use but what 3D modality the imaging physicians involved in TAVI are expert at. As the American humorist Seba Smith said in 1840 ”There are more ways than one to skin a cat" and there is certainly more than one way to size the aortic annulus well. References: 1- Vaquerizo B, Spaziano M, Alali J, Mylote D, Theriault-Lauzier P, Alfagih R, et al. Three-dimensional echocardiography vs. computed tomography for transcatheter aortic valve replacement sizing. Eur Heart J Cardiovasc Imaging. 2016;17(1):15-23. 2- Tsang W, Bateman MG, Weinert L, Pellegrini G, Mor-Avi V, Sugeng L, et al. Accuracy of aortic annular measurements obtained from three-dimensional echocardiography, CT and MRI: human in vitro and in vivo studies. Heart. 2012;98(15):1146-52. 3- Smith LA, Dworakowski R, Bhan A, Delithanasis I, Hancock J, Maccarthy PA, et al. Real-time three-dimensional transesophageal echocardiography adds value to transcatheter aortic valve implantation. J Am Soc Echocardiogr. 2013;26(4):359-69. 4- Khalique OK, Kodali SK, Paradis JM, Nazif TM, Williams MR, Einstein AJ, et al. Aortic annular sizing using a novel 3-dimensional echocardiographic method: use and comparison with cardiac computed tomography. Circ Cardiovasc Imaging. 2014;7(1):155-63. 5- Altiok E, Koos R, Schroder J, Brehmer K, Hamada S, Becker M, et al. Comparison of two-dimensional and three-dimensional imaging techniques for measurement of aortic annulus diameters before transcatheter aortic valve implantation. Heart. 2011;97(19):1578-84.