Introduction
Related and previous work
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Anatomy The MV apparatus, potentially patient-specific, should be integrated, including the annulus, leaflets, chordae tendineae, and papillary muscles.
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Hemodynamic environment The simulator should generate a hemodynamic environment for realistic behaviors in physiological, pathological, and repaired conditions for prosthetic, porcine, and patient-specific MVs.
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Therapy Physicians should be able to perform MIMVS in the rested simulator and TEER in the beating simulator. Therefore, the simulator should provide access to the MVs, and allow for observations and manipulations similar to those during the intervention.
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Observations and measurements It should be possible to perform detailed quantitative and qualitative evaluation of the hemodynamic situation via flow-, and pressure measurement, visual observation, and transesophageal echocardiography (TEE) to assess the MV and the success of repair.
Simulator design
Simulator validation
Experiments
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The Biological valve was a 31 mm MV prosthesis (T510C31, Medtronic plc, Dublin, Ireland).
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The Mechanical valve was a 21 mm MV prosthesis (21 MHPJ-505, Abbott Laboratories, Illinois, USA).
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The ex-vivo valve A (for MIMVS) was sewn into a well-sized elliptical (40 mm long and 30 mm wide) frame respecting the physiological proportions of the mitral fibrous annulus.
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The ex-vivo valve B (for TEER) was sewn into an oversized circular frame to mimic annulus dilatation. (50 mm diameter).
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The in-vitro valve was generated according to Engelhardt et al. [9] from the TEE of a patient with bi-leaflet prolapse. First, the MV was segmented and a surface mesh created. After inverting the mesh, it was combined with virtual geometries to create a negative casting mold, which was subsequently 3D-printed. Additionally to the method introduced by Engelhardt et al., a gauze mesh for the leaflets and threads for the chordae tendineae were inserted before casting to reinforce the silicone. The reinforcement with fabric, which was first introduced by Ginty et al. [12], was necessary due to a small Young’s modulus (~ 0.5 MPa) and high extensibility (~ 900%) of the silicone alone. MV structures such as primary chordae tendineae have a higher Young’s modulus (~ 85 MPa) and a lower extensibility (4.3%), so an MV solely out of silicone would lead to an excessive strain during systole [15].
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At first, the biological and mechanical valves were installed in the simulator to validate the simulator’s baseline at the physiological range.
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Ex-vivo valve A was then installed in a physiological state, and measurements were acquired. Primary chordae tendineae were cut at the posterior leaflet (P2–P3-segment) to induce a pathological condition. Finally, an MIMVS, consisting of two neo-chordae implantations, was performed to restore physiological MV function. During MIMVS, the LA (Fig. 1b) was replaced by the MIMVS-head (Fig. 1c).
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In the subsequent experiment, TEER was performed on the dilated MV (ex-vivo valve B) under TEE and video vision. Livestream via an action camera replaced fluoroscopy to avoid radiation. One Pascal Clip was placed between the segments A2–P2.
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Finally, the silicone patient-specific valve replica (in-vitro valve) with a bi-leaflet prolapse was tested in a pathological state and again after performing MIMVS. Specifically, a Chordae-Loop 20 mm (CV-4 needle) was implanted at the anterolateral papillary muscle, and all four loops were fixed at segments A1, A2, A3, and P1 with Cardionyl® 4/0 (Peters Surgical, Boulogne-Billancourt, France). Then, after sizing, annuloplasty was performed using a 36 mm Mitral Annuloplasty Memo 4D Ring (LivaNova PLC, London, UK).
Data acquisition and processing
Evaluation
Results
Prosthetic valves | Ex-vivo valve A | Ex-vivo valve B | In-vitro valve | ||||||
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Biological | Mechanical | Physio | Patho | Repaired | Patho | Repaired | Patho | Repaired | |
Compliance volume (ml) | 130 | 130 | 100 | 100 | 100 | 40 | 40 | 0 | 0 |
Systolic blood pressure (mmHG) | 118 | 119 | 120 | 85 | 117 | 99 | 106 | 79 | 115 |
Trans mitral gradient (mmHg) | 3.21 | 6.69 | 0.72 | 0.72 | 1.49 | 2.32 | 2.51 | 6.86 | 13.5 |
Stroke volume (ml) | 61 | 61 | 57 | 44 | 58 | 45 | 54 | 37 | 48 |
Cardiac output (l min−1) | 4.88 | 4.90 | 4.55 | 3.49 | 4.67 | 3.56 | 4.3 | 2.98 | 3.83 |
Regurgitation volume (ml) | 3 | 4 | 9 | 24 | 8 | 24 | 15 | 32 | 22 |
Regurgitation fraction (%) | 5 | 6 | 14 | 35 | 12 | 35 | 22 | 47 | 32 |
Mitral regurgitation grade | 0 | 0 | 0 | 2 | 0 | 2 | 1 | 2.3 | 1 |
PLVMS (mmHg) | 819 | 814 | 821 | 809 | 824 | 813 | 812 | 803 | 814 |
PLVED (mmHG) | 782 | 783 | 788 | 789 | 795 | 788 | 789 | 781 | 782 |
Mitral Valves | |||
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Physiological | Pathological | Repaired | |
Systolic blood pressure (mmHg) | 119 ± 1 | 88 ± 8 | 113 ± 5 |
Cardiac output (l min−1) | 4.78 ± 0.16 | 3.34 ± 0.26 | 4.27 ± 0.34 |
Stroke volume (ml) | 60 ± 2 | 42 ± 3 | 53 ± 4 |
Regurgitation volume (ml) | 5 ± 3 | 27 ± 4 | 15 ± 5 |
Regurgitation fraction (%) | 8 ± 4 | 39 ± 5 | 21 ± 7 |