Feasibility of Three-dimensional Printing in Transcatheter Tricuspid Valve Replacement after Surgical Mitral Valve Replacement

Abstract

Objectives

Our goal was to investigate the feasibility of applying 3-dimensional printing when treating 10 patients with severe tricuspid regurgitation (TR) secondary to surgical mitral valve replacement (SMVR) who received transcatheter tricuspid valve replacement (TTVR).

Background

Previous studies have shown that many patients develop TR secondary to SMVR and that functional TR is associated with more in-hospital deaths and poor clinical outcomes. Many transcatheter devices are currently in early-stage clinical trials, and little is known about the feasibility, safety, and outcomes of the reduction of TR resulting from TTVR for most of these devices.

Methods

From September 2020 to December 2021, a total of 10 patients [6 women (60.0%)] with severe or extremely severe TR secondary to SMVR in Xijing Hospital were enrolled. The preoperative tricuspid valve (TV) models of the 10 patients were reconstructed, printed, and simulated for the bench test. All patients underwent TTVR with the LuX-Valve. The patients were treated via the right atrial surgical approach. The valve was implanted under the guidance of X-ray fluoroscopy and intraoperative transesophageal echocardiography (TEE). Echocardiography data and clinical outcomes were collected at baseline, before discharge, and at follow-up examinations at 30 days and 6 months.

Results

The patients’ baseline characteristics showed a large comorbidity burden [severe TR, reduced right ventricular (RV) function at baseline]. The bioprostheses were successfully implanted in all 10 patients without device-related adverse events. The durations of the procedures were 140.0 (IQR: 120.0, 172.5) minutes, and the time in the intensive care unit was 3.0 (IQR: 2.0, 3.5) days. None of the patients died or experienced valvular events at 6 months of follow-up after the implant; they showed evidence of RV remodeling and increased cardiac output. TR continued to decrease in 10 patients from baseline to 6 month follows-up, with 10 (100.0%) patients experiencing a ≥ 2 grade reduction. All patients (100.0%) reached primary end points. Six patients were in New York Heart Association (NYHA) functional class I, four patients were in NYHA functional class II, and no device-related complications occurred. In addition, the 6-minute walking test showed significant improvement in motion performance [378.0 (IQR: 351.5, 406.5) m vs. 330 (IQR: 265.0, 351.5) m, p = 2.13×10^− 5]. Kansas City cardiomyopathy questionnaire scores also improved significantly at the 6-month follow-up [63.33 (IQR: 54.59, 71.50) vs. 36.17 (IQR: 31.17, 40.42), p = 3.63×10^− 5].

Conclusions

It is feasible to use 3-dimensional printing to guide placement of the LuX-Valve in the treatment of patients with severe TR, thereby effectively improving the success rate of the operation and reducing the incidence of complications. The majority of patients with TTVR exhibited RV remodeling, increased cardiac output, and improvement in NYHA functional class. The technology has the potential to be rapidly integrated into clinical practice to assist in decision making, procedural planning, and training. In the meantime, further research is needed to determine the long-term outcomes of TTVR.

Introduction

Functional or secondary tricuspid regurgitation (TR) is a progressive disease with a significant impact on mortality [1,2]. In recent years, interest has increased in functional or secondary TR and in the recognition of the progressive nature of the disease and its impact on mortality [3]. Studies have shown that TR is not uncommon after left heart valve surgery [4,5]. When the prosthesis is in the left heart, it causes local deformation of the anatomical structures and aggravates the deformation and enlargement of the tricuspid valve, resulting in TV insufficiency [6]. Currently, TV surgery is associated with a high surgical risk and a poor long-term prognosis. Although the number of reparative operations is increasing, high rates of recurrence within 5 years of repair were reported [7]. Data from the Society of Thoracic Surgeons (STS) database between 2000 and 2010 showed that the overall 5-year, 10-year, and 15-year survival rates after TV surgery were 54%, 29%, and 13%, respectively [8]. Due to the high surgical mortality rate of patients with TV disease, interest in replacing surgical interventions with transcatheter replacements has increased. Many devices have been developed, resulting in varying degrees of reduction in TR [9,10]. Recent data from the Valve-in-Valve International Database registry showed that transcatheter tricuspid valve replacement (TTVR) can be performed successfully and safely after prior surgical repair or bioprosthetic valve replacement, with favorable short-term results in the majority of patients [11,12]. In addition, a report of in situ TTVR from a single center demonstrated its feasibility and effectiveness [13,14]. However, surgical mitral valve replacement (SMVR) with TTVR for severe TR is still extremely challenging [15]. Therefore, a comprehensive and quantitative assessment of the pathological anatomical structures of TV is required in order to plan the operation properly.

Because heart valves have complex three-dimensional (3D) structures, traditional two-dimensional (2D) imaging is often insufficient to provide an accurate morphological assessment. 3D printing has made great progress during the past decades [16]. 3D printers now have the ability to print scale models from almost any type of material, and they have been used in a variety of biomedical applications [16,17]. They have incredible spatial resolution that permits one to study and understand microscopic details. Moreover, the use of 3D simulation in training and preoperative planning has demonstrated excellent results in cardiology and cardiovascular medicine [17,18]. It is more challenging to evaluate the TV using conventional 2D imaging than it is to evaluate the mitral valve, which is critical to identify patients with severe TR after left heart valve surgery [19]. In view of these findings, it is important to understand the impact of 3D printing on postoperative outcomes associated with TTVR, including the impact of related complications. Therefore, the goal of this study was to evaluate the feasibility of 3D printing guidance on TTVR and its effectiveness on prognosis.

Methods

Baseline Characteristics

From September 2020 to December 2021, a total of 10 patients with TR after SMVR (women, 60.0%, 64.0 IQR:60.5, 68.0 years) were enrolled in this study. The severity of TR in the study was classified as mild, moderate, severe, very severe, and extremely severe [20]. All patients were carefully evaluated by the multidisciplinary cardiac team and considered to be either contraindicated or at high risk for an operation. Exclusion criteria included a left ventricular ejection fraction <35%, tricuspid ring systolic displacement <10 mm, change fraction of the right ventricular (RV) area <20%, and systolic pulmonary arterial pressure >60 mmHg (1 mmHg=0.133 kPa). The clinical trial was registered in the ClinicalTrials.gov Protocol Registration System (NCT02917980). All procedures were carried out in accordance with the ethical guidelines set out in the Declaration of Helsinki, and all patients signed the informed consent forms.

Device Description

The LuX-Valve (Jenscare Biotechnology, Ningbo, China) consists of a biological valve stent, three valve lobules, and a steerable delivery system (Figure 1). The bovine pericardial valve leaflets received GeniGal anticalcification treatment to improve durability. The interventricular anchor was used to solve the problem of TV fixation. The atrium disc is a leak-proof ring whose position can be adapted as needed, with no pressure on the tissues around the TV. The clamping device of the anterior valve provides both positioning and ventricular septal anchoring functions to form stable anchoring.

Preprocedural Imaging

Coronary angiography was used to exclude severe coronary artery diseases, invasive RV catheterization was used to evaluate the hemodynamics of the right heart, and computed tomography angiography (CTA) was used to evaluate the anatomical structures. Functional TR is considered to be a disease that depends not only on the sizing and shape of the TV but also on the function of the RV, ventricular septal displacement, and pulmonary arterial pressure [21]. Transthoracic echocardiography was performed in all patients preoperatively to assess the RV and TV functions (Figure 2).

Reconstruction of 3-Dimensional Printed Models and Surgical Simulation

First, the patients' CT data were imported into Materialise Mimics version 21.0 (Materialise, Leuven, Belgium). Three orthogonal slices (coronal, sagittal, and cross sectional) were created using interactive multiplane imaging reconstruction. After completing the comparison and the confirmation, the contour area was reconstructed to obtain the initial 3D model of RV. The collected images were converted to the standard format of Digital Imaging and Communication of Medicine for storage. Secondly, a comprehensive reconstruction of RV morphology was performed using Materialise 3-matic software (Materialise). Different parts of the digital model were distinguished by different colors to represent the multidimensional structural format of each part. Finally, the digital model was exported to Standard Tessellation Language format. Then the Standard Tessellation Language files were imported into a Polyjet 850 multimaterial full-color 3D printer (Stratasys, Inc., Eden Prairie, MN, USA) for printing, different materials were selected to match different tissues. The main steps of TTVR were simulated in the bench test for all patients in the 3D printing group (Figure 3).

Procedural Steps

The procedure was performed in the intubation laboratory. After the patient received general anesthesia, the TV was entered via a right minimally invasive thoracotomy and through the right atrial (RA) path. TEE and X-ray fluoroscopy were used to guide the procedure. TEE was used mainly to guide catheter delivery, valve release, and adjustment of the intraoperative valve position (Figure 4A). A coronary artery guide wire was placed in the right coronary artery to help determine the annulus plane of the TV. Heparin was administered systemically to achieve an activated coagulation time of >200 s, then 4-0 Prolene sutures with felt sheets were used with a double purse-string suture in the RA. The delivery catheter was placed into the RV under the guidance of TEE and X-ray fluoroscopy. The angle of the catheter was adjusted to ensure that the catheter was coaxial and centered with the ring (Figure 4B). When the catheter was under the loop of approximately 5 cm, the interventricular septum anchor, valve, and two clamping keys of the anterior lobes were released in turn by adjusting the knob system on the catheter (Figure 4C). Then, the clamping keys were positioned properly under the anterior lobe, and the entire delivery system was gently retracted so that the clamping keys hooked the anterior lobe (Figure 4D). The atrial plate was released, the interventricular septal anchor was deployed, and the anchor pin was inserted into the septum for fixation (Figure 4E). Finally, the catheter was withdrawn and removed. The heparin was neutralized, and the atrial incision was closed. Postoperative TEE showed that the TR disappeared immediately (Figure 4F).

Follow-Up

Follow-up data were collected from the enrolled patients at baseline, before discharge, and 30 days and 6 months after the TTVR. Primary end points included successful surgery and successful device implantation. Successful surgery was defined as successful implantation of the valve and removal of the delivery system, and the correct and stable placement of the prosthesis, with no serious or life-threatening adverse events during the operation. In addition, the function of the TV was recovered satisfactorily (TR severity was reduced by ≥2, TV pressure gradient by ≤6 mmHg), and there were no cardiovascular-related deaths, implant displacements, valve failures, or other device-related major adverse events (including myocardial infarction, embolism, conduction disturbances, and new transventricular septal shunt).

Statistical Analyses

Continuous variables were reported as the median (25th and 75th percentile), whereas classified variables were expressed by frequency and percentage. The paired t-test was used to compare continuous variables for each patient before and after the procedures, and other continuous variables were determined with the Student t-test or one-way analysis of variance. We compared the classification variables using the χ² test. A two-tailed P-value of <0.05 was considered statistically significant. All statistical analyses were conducted using the Statistical Package for Social Sciences (SPSS, Chicago, IL, USA) version 26.0.

Results

Baseline Data

The baseline clinical features of the 10 patients are listed in Table 1. Despite being treated with aggressive diuretic therapies, patients of both groups exhibited typical symptoms of severe right heart failure with ascites (40.0%) or peripheral edema (100.0%), and 6 (60.0%) patients had pulmonary hypertension before TTVR. The causes of TR were left valve surgery (100%) without permanent pacemaker or cardioverter defibrillator implantation, and all patients had AF. In addition, all patients (100.0%) were in New York Heart Association (NYHA) functional class III/IV. The Society of Thoracic Surgeons (STS) score was 8.474 (IQR: 6.309, 9.584) %, which indicated a high risk for cardiopulmonary bypass. Preprocedural CTA and echocardiographic parameters are listed in Table 2. All 10 patients had severe TR at baseline. Preoperative right heart catheterization showed that the mean pulmonary artery pressure (mPAP) of the included patients was 25.5 (IQR: 23.0, 27.5) mmHg. In addition, the maximum diameter of the TV annulus (TA) was 52.2 (IQR: 48.3, 53.3) mm, the minimum diameter was 46.0 (IQR: 40.2, 46.8) mm, the systolic excursion of the tricuspid annular plane (TAPSE) was 13.2 (IQR: 11.9, 14.5) mm, and the mean TV pressure gradient (TVPG) was 12.5 (IQR: 11.5, 17.0) mmHg.

Intraoperative and Hospitalization Data

The intraoperative and hospitalization details are shown in Table 3. All patients were treated 3 to 5 days preoperatively and, if tolerated, were treated with intravenous diuretics to reduce weight and improve peripheral edema. Surgical success was achieved in all patients (100%), with the individual bioprostheses in place in all cases. The procedural time was 140.0 (IQR: 120.0, 172.5) min, the device time was 13.0 (IQR: 10.0, 17.5) min, the fluoroscopy time was 20.5 (IQR:18.0, 24.5) min, with no persistent ventricular arrhythmias, atrioventricular block, or cardiac rupture. All patients (100.0%) had no/trace regurgitation. The time in the postoperative intensive care unit was 3.0 (IQR: 2.0, 3.5) days, and the number of postoperative days in the hospital days was 12.0 (IQR: 9.5, 13.5). In patients with no pre-existing renal impairment, RV angiography was performed to confirm the position and function of the implanted valve. Before discharge, computed tomographic scans confirmed the position and fixation details of the prosthesis. CTA data from all 10 patients were used for 3D reconstruction, and 3D models were printed to verify postoperative morphology and function (Figure 4G, H). In addition, there were no pulmonary embolisms, cerebrovascular events, or new conduction blocks during hospitalization. All discharged patients were treated with anticoagulants.

30-Day and 6-Month Follow-Up Data

Details of follow-up echocardiographic data are shown in Table 4 and Figure 5. The mean pressure gradient was 3.0 (2.0, 3.5) mmHg 30 days postoperatively. For all 10 patients, TR severity measured by transthoracic echocardiography decreased from 100.0% with severe regurgitation to 100.0% with no/trace regurgitation. Of the remaining patients, patient #7 (10.0%) had mild regurgitation. The TV annulus diameter and RV length diameter were both decreased compared with preoperative measurements, indicating RV remodeling. At the 6-month follow-up, 6 patients (60.0%) were NYHA functional class I, 4 patients (40.0%) were NYHA functional class II, and no device-related complications occurred. All patients exhibited significant improvement in symptoms at 6 months. From the follow-up data, TR decreased to no/trace in 9 patients (90.0%). In addition, the reduction of the TV ring diameter and the increased deviation of the TV annular plane in systole indicated improvement in RV structure and function. The 6-minute walking test results showed significant improvement in motion performance [378.0 (IQR: 351.5, 406.5) m vs. 330 (IQR: 265.0, 351.5) m, p=2.13×10^-5]. Kansas City cardiomyopathy questionnaire scores also improved significantly at the 6-month follow-up [63.33 (IQR: 54.59, 71.50) vs. 36.17 (IQR: 31.17, 40.42), p=3.63×10^-5]. All patients (100.0%) met the primary end point.

Discussion

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.

Conclusion

Patients with severe functional TR were treated with TTVR, which is a feasible, relatively safe, low-complication approach that improves RV remodeling and cardiac output with reliable clinical outcomes in patients after SMVR. Using 3D printing to guide TTVR, 3D printed models of TV allow for morphological and quantitative analyses of the TV and the left heart with a high degree of fidelity. Therefore, 3D printing has great potential to be integrated into clinical practice to assist in decision making, surgical or interventional planning, and medical training. As a next step, device iterations are needed to reduce invasiveness and improve patient selection criteria to enhance the safety of the procedure and to organize larger prospective studies to assess the impact on long-term clinical outcomes.

Declarations

Clinical Trial Registration

ClinicalTrials.gov Protocol Registration System (NCT02917980). 

Acknowledgements

We would like to thank Make Medical Technology Co., LTD. (Xi’an, China) for supplying the 3D printed models.

Author Declarations

Funding

This work was supported by the National Key R&D Program of China (No. 2020YFC2008100), the Shaanxi Province Innovation Capability Support Plan – Innovative Talent Promotion Plan (No. 2020TD-034), and the Discipline Boosting Program of Xijing Hospital (No. XJZT18MJ69).

Conflicts of interest

The authors have no conflicts of interest to declare.

Availability of data and material

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Code availability

Not applicable.

Authors’ contributions

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

Ethics approval

The studies involving human participants were reviewed and approved by Clinicaltrials Organization: Xijing Hospital, Air Force Medical University.

Consent to participate

The patients/participants provided their written informed consent to participate in this study.

Consent for publication

Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

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Tables

Table 1. Baseline patient characteristics 

*Defined as eGFR <60 mL/min. 

†Defined as MELD-albumin score >12. 

BMI: body mass index, CKD: chronic kidney disease, COPD: chronic obstructive pulmonary disease, eGFR: estimated glomerular filtration rate, KCCQ: Kansas City Cardiomyopathy Questionnaire, LBBB: left bundle branch block, MELD: Model For End-Stage Liver Disease, mPAP: mean pulmonary artery pressure, NT-proBNP: N-terminal pro-B-type natriuretic peptide, NYHA: New York Heart Association, RBBB: right bundle branch block, 6MWT: 6-minute walk test, STS: Society of Thoracic Surgeons, TIA: transient ischemic attack. 

Table 2. Baseline echocardiographic and computed tomography parameters 

EROA: effective regurgitation orifice area, LVEF: left ventricular ejection fraction, LVIDD: left ventricular internal dimension in diastole, LVIDS: left ventricular internal dimension in systole, PISA: proximal isovelocity surface area, RA: right atrium, RV: right ventricular, TA: tricuspid valve annulus, TAPSE: tricuspid annular plane systolic excursion, TR: tricuspid regurgitation. 

Table 3. Intraoperative and in-hospital outcomes 

*Defined as the duration from initial skin incision to final wound closure. 

†Defined as the duration from guiding sheath insertion into the RA to retrieval of the delivery system. ICU: intensive care unit, TIA: transient ischemic attack, TR: tricuspid regurgitation. 

Table 4. Baseline to 6-month echocardiographic measurements 

Values are presented as N (%) or median (25th, 75th percentile). 

EROA: effective regurgitation orifice area, LA: left atrium, LV: left ventricle, LVEF: left ventricular ejection fraction, PISA: proximal isovelocity surface area, RA: right atrium, RV: right ventricle, TAPSE: tricuspid annular plane systolic excursion, TR: tricuspid regurgitation, TVPG: tricuspid valve pressure gradient.