Preoperative evaluation derived from CT based on the multi-plane reconstruction function of measurement software such as 3-mensio is regarded as the golden standard for TAVR patients now, obvious contrast between the lumen and the myocardium/vascular wall enable its significant performance in distinguish vascular and non-vascular structures. However, the use of contrast and exposure to ionizing radiation limit its application in some special patients who are allergic to contrast agents or suffered from renal insufficiency. 3D-TEE was expected to act as an alternative method for these patients. Different from CT, there is no mature or uniform TEE - based preoperative evaluation method. 2D-TEE was the initial resource, however, as the structures been measured were usually oval instead of perfectly round, this measurement tended to severely underestimate the results. With the popularization of 3D-TEE, it replaced 2D-TEE and was widely used in preoperative evaluation of TAVR patients. Arnold (11) used the q-lab (Philips Medical Systems) to measure the aortic annulus and LVOT by the same multi-plane reconstruction method as CT. Omar (12) evaluated the aortic root by off-label using of mitral valve measurement software Mitral Valve Quantification (Philips Medical Systems). A semi-automated software specifically designed for aortic root was used by Mediratta and his colleagues (13), and two automated software Aortic Valve Navigator (Philips Medical Systems) and eSieValvesTM (Siemens Medical) had been applied by Edgard(14) and Nahoko(15), respectively. Despite improvements in software, the above studies generally showed that measurement based on 3D-TEE were still significantly smaller than those based on CT. We considered that the inconsistency between the methods and software might be important factors contributed to the measurement differences. Therefore, we chose the same Mimics software to evaluate CT and 3D-TEE images in order to eliminate the possible error. However, the final results did not show as we expected. The difference had not been significantly reduced. Even though, good correlation and agreement between them still enabled 3D-TEE to be used as preoperative imaging data in TAVR patients contraindicated for CT examination. Figure 2 shows the regression equation between CT and 3D-TEE measurements regarding to annulus and LVOT.
Severe calcification will significantly deteriorate the image quality of 3D-TEE because of the artifact generated by it, thus impede the measurement and reduce the accuracy in theory. However, our research failed to come to the expected conclusion. Calcification didn’t show an obvious correlation to the differences between 3D-TEE and CT measurements of annulus diameters. The value of HU450 and HU850 in predicting the discrepancy was also limited from the analysis of ROC curve. In fact, in our research we found that calcification was not always a negative factor, its highlighting signal can sometimes help to distinguish valve leaflet and locate annulus, and this may partly account for the results.
What’s new about our research is not only that we used the same software and method for 3D-TEE and CT measurement, but also we had expanded the patient sample and measurement parameters. Due to the lacking of calcification which was essential for the bioprosthetic valves to anchor in the early cases, pure AR patients were once considered as contraindicated for TAVR (16). In recent years, CoreValve (Medtronic Inc., Minneapolis, USA) (17) and SAPIEN XT (Edwards Lifesciences Inc., Irvine, USA) (18)with the help of some special designs, and some new valves dedicated for AR patients such as JenaValve (JenaValve Technology GmbH, Munich, Germany) (19), J-valve (Jie Cheng Medical ltd., Su Zhou, China) (20), and ACURATE series (Symetis SA, Ecublens, Switzerland)(21, 22) had started to be used for the treatment of them. To our knowledge, this is one of the first studies with pure AR patients included. Preoperative evaluation of TAVR mainly included diameter measurements of aortic annulus, LVOT, SOV, STJ and ascending aorta(AAO), and assessment of coronary artery height, left ventricular aortic angle, valve type and calcification, optimal angiographic projection angle and peripheral vascular anatomy, etc. Each parameter plays an important role in strategy making. Accurate acquisition of diameters of annulus and other structures can help to choose the most appropriate bioprosthesis valve and the best deployment area to prevent complications such as valve migration and PVL. Coronary height and SOV volume are critical indicators to judge the risk of myocardial infarction. Left ventricular aorta angle and peripheral blood vessel evaluation are essential in selection of a better approach and the optimal angiographic projection angle enables the performers to get the best surgical vision. Different from the previous researches which mainly focused on annulus, we had also compared the measurement of LVOT、SOV and STJ, and the results showed 3D-TEE can be used as an alternative for their evaluation.
How to reach the most accurate preoperative evaluation has always been the most concerned issue. In addition to making full use of image resources, the emergence of 3D printing technology provides new ideas for us. Through in vitro reconstruction of patient-specific aortic root model and precise presentation of anatomical structure, 3D printing model has showed its significant role in preoperative evaluation of TAVR patients. In the future, with the development of 3D printing materials, and the combination with the finite element analysis technology, we look forward to select the best operation strategy and forecast operation results by computer simulation before operation, so as to further improve success rate and reduce the risk of complications.