First Experience With a Novel Self‐Expandable Valve for Mitral Annular Calcification Guided by Three‐Dimensional Printing

ABSTRACT

Transcatheter mitral valve replacement (TMVR) may emerge as a surgical alternative for high‐risk patients with severe mitral annular calcification (MAC), yet several questions remain to be addressed. We present the case of a 67‐year‐old high‐risk female patient with severe MAC (MAC score = 8) and mitral stenosis (effective orifice area = 121.3 mm²). To avoid conventional high‐risk surgery, we opted to perform the TMVR using the novel Mi‐thos system via the transapical approach. We utilized a patient‐specific three‐dimensional printed model derived by preprocedural computed tomography angiography data to assess the feasibility of the novel device and to guide the operation, mitigating potential challenges. The successful outcome of the guided procedure led to symptomatic improvement in the patient. This case represents the first experience with the novel Mi‐thos system for TMVR in a patient with severe MAC. Guided by a patient‐specific three‐dimensional printed model, the dedicated transcatheter heart valve may be a feasible and safe option for high‐risk patients with severe MAC.

1. Introduction

Mitral annular calcification (MAC) is a degenerative process affecting the mitral annulus, with prevalence rates between 4.3% and 15%, increasing with age and other risk factors [1, 2]. Greater anatomical severity of MAC may indicate advanced disease progression. Over half of patients with mitral stenosis (MS) and MAC are estimated to forgo surgery, even when indicated [3, 4, 5]. Addressing this challenge requires achieving durable quality without compromising annular and ventricular function [3, 4, 5, 6, 7, 8].

The growing use of transcatheter techniques in structural heart disease may expand treatment options for high‐risk surgery patients [9, 10, 11, 12]. However, in severe MAC cases, the efficacy of these techniques may be influenced by the complex MV anatomy and challenging LV geometry [9, 10]. Additionally, commercially available THVs are often used “off‐label” for the valve‐in‐MAC (ViMAC) concept, and their clinical efficacy in this context remains controversial [8].

In recent years, cardiovascular 3D printing technology has proven valuable for preprocedural assessment in guiding transcatheter interventions for structural heart disease and evaluating novel devices [11, 12, 13]. We present our first experience with the Mi‐thos transcatheter mitral valve replacement (TMVR) system (New Medicine Medical Co. Ltd., Shanghai, China) for a patient with severe MAC via the transapical approach. To optimize planning and assess potential risks, we created a patient‐specific 3D‐printed model to simulate essential procedural steps.

2. Case Presentation

A 67‐year‐old female patient was admitted to a local hospital 1 month previously due to chest tightness, shortness of breath, pulmonary edema, and peripheral edema. Despite receiving optimal medication including metoprolol (1*200 mg), furosemide (2*100 mg), dagliazine (1*10 mg), and spironolactone (1*30 mg), the patient continued to exhibit limited motor capacity (New York Heart Association functional class IV).

Following referral to our center, transesophageal echocardiography (TEE) images and computed tomography angiography (CTA) scans revealed a severe MAC (MAC score 8) [13] and MS (effective orifice area = 121.3 mm²; PG_mean = 15 mmHg, V_max = 191 cm/s) (Figure 1) combined with LV ejection fraction of 45%. The patient had a history of stroke.

Figure 1.

Preoperative imaging assessments. (A and B) Preoperative echocardiography revealed mitral stenosis (PG_mean= 15 mmHg, V_max = 191 cm/s) and mitral annular calcification area. (C–I) Preoperative computed tomography angiography was used to access the mitral valve anatomy and the left ventricular outflow tract. (C) The area of the mitral effective orifice area = 121.3 mm². (E and F) The area of the neo‐left ventricular outflow tract after implanting the 29‐mm balloon‐expandable bioprosthesis was 179.5 mm², and no obstruction occurred. (G–I) The area of the neo‐left ventricular outflow tract after implanting the 29‐mm Mi‐thos system was 176.2 mm², and no obstruction occurred. The projection angle of the released implanted valve was RAO26, CAU35. [Color figure can be viewed at wileyonlinelibrary.com]

After discussing all available treatment options and considering the patient's prohibit surgical risk (Society of Thoracic Surgery risk score 11.192%; European System for Cardiac Operative Risk Evaluation Score II 8.3%), the cardiac team decided to perform TMVR.

3. Patient‐Specific Three‐Dimensional Printed Model and Bench‐Test Simulation

We utilized the patient's CTA data to thoroughly evaluate the circumferential extent, distribution, and severity of the MAC. This analysis allowed us to calculate the area of the mitral valve pore and to determine the degree of match between the intended digital implant device and the MAC. We used software to segment the images and export them in Standard Tessellation Language (STL) format. Subsequently, postprocessing of the STL format files was carried out using Materialize 3‐Matic software (Leuven, Belgium). The final STL file was then imported into the Polyjet 850 multimaterial full‐color 3D printer (Stratasys Inc., Eden Prairie, MN, USA).

During the bench‐test simulation, we explored the possibility of implanting balloon‐expandable THV of various sizes and revealed the occurrence of paravalvular leakage (PVL), device displacement, and stent compression. Hence, we assessed the feasibility of implanting the novel self‐expandable THV, the 29‐mm Mi‐thos system, and simulated its implantation in the bench‐test simulation. After deployment, the fully unfolded bioprosthetic valve could be clearly visualized in its intended position (Figure 2).

Figure 2.

Preoperative three‐dimensional printed model reconstructions and bench‐test simulation were used to formulate the procedural plan. (A–C) Three‐dimensional reconstruction and calculation of landing zone structures were based on computed tomography angiography data. (D and E) The views after implanting the bioprosthesis of the 29‐mm balloon‐expandable valve. (F and G) The simulation process of implanting the 29‐mm Mi‐thos system. (H and I) The stent was fully released and observed in the left atrial and the ventricular views. PVL, paravalvular leakage. [Color figure can be viewed at wileyonlinelibrary.com]

4. Investigative Device

The Mi‐thos system is a novel self‐expandable THV device [11, 14]. Its prosthesis is made of cross‐linked bovine pericardial tissue lobules encased in a nickel‐titanium frame. The stent features a double‐layer design, combining a d‐shaped external scaffold with a circular internal scaffold, specifically engineered to conform to saddle‐shaped MV anatomy and prevent compression of the pericardial tissue. The bioprosthesis includes a d‐shaped atrial disc that fits the mitral annulus, promoting proper valve positioning and reducing PVL risk, particularly in cases of irregularly calcified MAC. The ventricular portion has an anchoring mechanism with evenly distributed barbs to capture leaflets and calcified tissue, enhancing stability without relying solely on radial force from oversizing. The construction and dimensions chart are shown in Supporting Information S2: Supplement Materials.

5. TMVR Procedure

The TMVR procedure is performed under general anesthesia, guided by fluoroscopy and TEE. A 4‐cm incision is made on the left thoracic wall to access the LV apex. Sheaths are inserted into the right femoral artery and vein, with a temporary pacemaker electrode placed through the venous sheath into the right ventricle, and a pigtail catheter advanced from the femoral artery to the LV. The standard apical channel is secured with sutures, followed by puncture and insertion of a 6 Fr sheath. The procedure then involves exchanging the sheath for a 260‐cm Lunderquist super‐stiff steel wire (Cook Medical Inc., Bloomington, IN, USA). The delivery system is then inserted via the guidewire and advanced in a retrograde manner through the MV via the transapical approach, ultimately reaching the left atrium. The MV complex is then pre‐expanded using a 23‐mm balloon.

The 29‐mm Mi‐thos bioprosthesis was assembled onto a delivery system. The d‐shaped atrial disc was released in the left atrium and gradually withdrawn to the ventricle, ensuring it was fully seated against the mitral annulus and covered the MAC region. Under TEE and fluoroscopy guidance, the stent orientation was adjusted to eliminate PVL. The ventricular portion was then released and secured using the safety barb force, capturing the MAC and valve leaflets while maintaining rapid pacing at 140 bpm. Immediate ventricular angiography was performed to confirm the optimal position and shape of the device. The TEE images confirmed the absence of PVL or left ventricular outflow tract obstruction (PG_mean = 2 mmHg, V_max = 86 cm/s) (Figure 3). Following this step, the delivery system was withdrawn, the apical puncture site was sutured, the incision was closed, and the mechanical ventilation was replaced.

Figure 3.

The main steps of the procedure. (A) Fluoroscopy showed mitral annular calcification. (B) Balloon mitral valvuloplasty performed via the transapical approach. (C and D) The delivery system was advanced, and the atrial disc covered the mitral annular. (E–H) The stent was fully released, and fluoroscopy and transesophageal echocardiography revealed that the bioprosthesis was in a stable position and functioning well with no paravalvular leak. [Color figure can be viewed at wileyonlinelibrary.com]

6. Follow‐Up

The patient was discharged 5 days postoperatively, and the outpatient follow‐up 1 month after discharge indicated an improvement in the patient's condition (New York Heart Association functional class II). The outpatient echocardiographic scans showed a left ventricular ejection fraction of 58%, PG_mean = 2 mmHg, no PVL, and good valve leaflet activity. Based on the 3D digital model generated from postoperative 6‐months CTA data, the device was found to be in a favorable position and shape, without annular rupture or decalcification (Figure 4).

Figure 4.

Postprocedural digital three‐dimensional printed model verified the stable position of the stent without decalcification and paravalvular leakage. [Color figure can be viewed at wileyonlinelibrary.com]

7. Discussion

MAC is a challenging clinical disease [1, 2, 3, 4, 5]. It is often advanced, with myocardial invasion, posing difficulties for open surgical correction [3, 4, 5]. Challenges include potential for residual PVL and risk of atrioventricular sulcus rupture [3, 4]. While several surgical options are available to treat MV disease and reduce complications, Loulmet et al. [8] demonstrated that robotic MV resection and repair based on Carpentier principles had positive perioperative outcomes and decreasing long‐term mortality with increased technical expertise. However, this procedure is only available to surgeons with specialized MV surgery expertise.

In recent years, clinical application of various THVs has yielded remarkable results [10, 11, 12, 13, 14]. However, there is limited practical experience demonstrating the applicability of dedicated THVs to a wide range of MV diseases [9, 12]. This challenge arises from the unique characteristics of the structurally altered MV complex, which complicates assessing feasibility of transcatheter intervention and selecting suitable TMVR devices [11, 13, 15]. The benefits of 3D printing in transcatheter structural heart interventions are well‐documented [11, 12]. Preoperative assessment and in vitro simulation guided by 3D printing may offer an effective solution [11, 12]. Wang et al. [11] used a dedicated TMVR device to apply the valve‐in‐ring concept for patients with recurrent mitral regurgitation, demonstrating the feasibility of the preoperatively simulated procedure with no postoperative complications like valve embolism or PVL.

In this case report, we present a patient undergoing TMVR for severe MAC. A patient‐specific 3D‐printed model based on cardiac CTA was created to understand the MAC region and potential THV landing zones. This model facilitated discussions on THV type and size and allowed simulation of procedural steps and complications. 3D printing helped us investigate the device's characteristics and its compatibility with the patient. Simulations indicated that implanting a cylindrical THV into noncircular, caseous calcified areas resulted in significant PVL, even with the largest size, and posed risks of valve compression, displacement, and embolism in hard landing zones.

We simulated the preoperative application of the Mi‐thos system to the ViMAC concept using a patient‐specific 3D‐printed model. The results showed that the novel device with a large d‐type atrial disc effectively conforms to the native mitral annulus, ensuring the successful elimination of potential PVL [11, 14]. The stent's barbs enhance contact with the MAC area, facilitating THV anchoring and preventing embolism or displacement. Additionally, shorter stents reduce the risk of left ventricular outflow tract obstruction. Based on bench‐test simulations, we selected the 29‐mm Mi‐thos system for transapical implantation into the MAC area. No postoperative complications occurred, and the patient was in good condition. However, it is important to acknowledge that current cardiac 3D printing technology has significant limitations in utilizing tissue‐specific features to predict device‐host interactions. More advanced digital techniques and innovative methodological approaches may be necessary to enhance the accuracy and comprehensiveness of assessment outcomes.

8. Conclusions

This case report highlights the first experience with the Mi‐thos system using the ViMAC concept. The development of procedural plans under the guidance of 3D printing enhances the feasibility and safety of TMVR for special cases, which may provide valuable experience for the effective procedural strategies later.

Ethics Statement

The studies involving human participants were reviewed and approved by Clinicaltrials Organization: Xijing Hospital, Air Force Medical University. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting information.

Supporting information.

Data Availability Statement

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