In this single-center, observational study, the LuX-Valve was successfully implanted in all 10 patients, and good clinical treatment results were achieved without the complex TV anatomical structures and different etiologies. The unique anatomical structures and pathophysiological characteristics of TV make the design of the TTVR device difficult. Physiologically, the TV has a 3D structure similar to that of a saddle, it exhibits dynamic changes during the cardiac cycle to ensure that the valve closes completely. Primary TR is caused by congenital or acquired abnormalities of the TV itself. However, secondary (or functional) TR, which is far more common than primary TR, is secondary to excess RV pressure and/or volume load. When TR occurs, the TV loses its normal shape and dilates under the strain of the dilated RA and RV. Current study results did not recommend performing operations on isolated TR [22,23]. Secondary TR is an important complication of SMVR, resulting in a poor prognosis [24]. The pathogenesis of SMVR is still not fully elucidated, but it is mainly attributed to TV dysfunction. It is often caused by persistent pulmonary hypertension, mitral valve dysfunction, progressive aortic valve disease, or left ventricular failure. Atrial fibrillation after SMVR is also an important factor for TR [25]. Most studies have shown that the surgical mortality rate is as high as 9% to 11% [26-28], especially after SMVR, because the TV is relatively large, and the anatomical structures are squeezed and deformed by the prosthesis, which changes the shape of the TV and makes TTVR more challenging.
Multiple low-risk transcatheter treatments have recently been evaluated for symptomatic patients with severe TR. Kodali et al. published a 30-day follow-up study of TTVR in patients with TR (the TRISCEND trial) using the EVOQUE valve (Edwards Lifesciences, Irvine, CA, USA) [29]. Hahn et al. evaluated the feasibility and safety of TTVR in patients at extreme surgical risk [30]. These studies demonstrated the safety and technical feasibility of TTVR, with significant reductions in TR and clinical improvements. The LuX-Valve, a new TTVR device independent of radial support, has been successfully applied in the treatment of patients with severe TR. Using an RA approach, the artificial prosthesis is delivered from the catheter to the location for the autologous valve. Then, the artificial prosthesis replaces the function of the autologous valve, improves TR, and maintains the normal function of TV, thus ensuring TV hemodynamics, improving cardiac function, and achieving the overall purpose of the treatment. The study results highlight the usefulness of preoperative multimodal imaging and 3D printing as adjuncts to guide TTVR. From another perspective, TTVR is a viable intervention for patients with high-risk TR. In recent years, one of the major challenges in such interventions was to observe the complex 3D relationships of the cardiovascular anatomical structures. CTA and TEE are auxiliary to achieving a 3D reconstruction, they use multimodal images and 3D printing to create a patient-specific model of the right heart. This study results prove that a 3D printed TV model may be used to comprehensively evaluate the related anatomical structures and plan the interventional therapy. The 3D printed models allow the operator to view and simulate the nuances of lesions in a comprehensive way that cannot be achieved with 2D medical imaging. The patient-specific 3D printed models render the anatomical structures easier to visualize and the interactions between the device and the TV easier to understand.
From this small series of patients who developed severe TR after SMVR at the 6-month follow-up, the subsequent points are important mainly because they explain how to obtain guidance from 3D printing. First, the anatomical structures of the TV were reconstructed using CTA data, then the physical model was produced, which helped the surgeons to more accurately understand the anatomical structures surrounding the TV before beginning the procedures. Second, preoperative surgical simulation may help surgeons to quickly find the release location, select the best surgical approach, and predict the size of the prosthesis in advance, thereby effectively preventing the occurrence of perioperative complications. At the same time, 3D printing was also used for postoperative assessment to evaluate the morphology and position of the TV after TTVR and the relationship between the prosthesis and the important adjacent structures and to simulate whether complications may occur after the valve is implanted. Third, 3D printing was used to construct a TV model in vitro and intuitively display the important structures around the TV, which could be used for doctor–patient communication and procedural plan evaluation. At the same time, it could be used to cultivate young surgeons' knowledge and understanding of the disease and of the surgical procedures. Fourth, 3D printing may improve the success rate of the operation and reduce the cost of the operation by formulating the complicated procedures and the use of individualized devices.
Given the number of patients with functional TR following SMVR, TTVR, as distinct from traditional TR surgery under cardiopulmonary bypass, a large number of medical imaging evaluations will be required. The application of 3D printing in the guidance and evaluation of various kinds of TTVR may further individualize the surgical procedures and promote the continuous progress of the precision medical mode, which will certainly be advantageous for both patients and surgeons.
Study Limitations
The main limitation of this study is the small sample size. Analysis of a larger group of patients who had the left heart valve replaced is necessary to evaluate the advantages of 3D printing. Furthermore, standardization of intraoperative imaging is an integral part of the success of other device technologies [31]. Intraoperative measurements are largely determined by the surgeon and do not truly represent the complex 3D structures of the TV. Third, the 3D printed TV model does not allow the reproduction of the details of the anatomical structures, such as the precise positioning and distance between junctions [32]. Finally, many patients do not have a comprehensive assessment of the RV and TV after having implants, which limits the ability to accurately predict efficacy and clinical outcomes. Further intermediate and long-term follow-up examinations are required to assess the safety and efficacy of TTVR. In addition, anticoagulation is necessary for an RV with low pressure, but the short-term follow-up data are not adequate to provide recommendations for anticoagulation used with existing devices.