The following are key points to remember from this review article on transseptal transcatheter mitral valve replacement (TMVR) using balloon-expandable transcatheter heart valves:

1. At present, candidates for TMVR are patients with severe symptomatic mitral valve disease and a failing bioprosthesis or ring annuloplasty or mitral annular calcification for whom the risk-benefit ratio favors intervention over medical treatment and the heart team favors a nonsurgical approach. The objectives of the screening process for TMVR are to identify the severity and mechanisms of mitral valve disease and bioprosthesis or ring failure; determine the morphology of the mitral valve and specific characteristics of surgical bioprostheses or rings; determine the risk of complications such as left ventricular outflow tract (LVOT) obstruction, paravalvular leaks, or embolization; and help in the planning of the procedure.
2. In general, patient preparation and room setting (catheterization laboratory or hybrid room) do not differ from those of transcatheter aortic valve replacement (TAVR) with general anesthesia. The permanent presence of a skilled interventional echocardiographer is mandatory throughout the procedure for continuous transesophageal echocardiography (TEE) guidance.
3. Once the catheter has been correctly placed in front of the mitral orifice, an antegrade crossing is obtained using a 5F diagnostic catheter, mainly multipurpose, pigtail, or amplatz catheters mounted on a standard 0.0035-inch J wire.
4. The transcatheter heart valve (THV) preparation follows the general principles of Edwards valve preparation, with two specificities: an overfilling of an additional 2-3 cm³ in the inflation syringe is recommended in valve-in-valve and valve-in-ring cases, to secure anchoring and avoid secondary atrial migration by achieving a flared appearance of the prosthesis in its ventricular part and the orientation of the THV on the balloon catheter is critically important with the SAPIEN XT/3 THV mounted for antegrade implantation (similar to the position in transapical aortic valve procedures) on the catheter.
5. The atrial septum is dilated using 12- to 16-mm peripheral balloons such as the ATLAS catheter balloon, the IMPACT catheter balloon, the Mustang balloon, or similar balloons tracked on the stiff wire.
6. After careful checking of its orientation, the prosthesis is advanced through the sheath, aligned, and adjusted in the inferior vena cava, exactly as is done in the descending aorta during TAVR.
7. The remainder of the procedure is performed in the projection perpendicular to the plane of the mitral bioprosthesis, ring, or annulus. Once the position of the THV is deemed adequate, it can be deployed under rapid ventricular pacing. The first operator holds the catheter in the left hand and the wire in the right, to be able to finely adjust the position of the THV during its deployment, while the balloon is inflated by the second operator.
8. After deployment, a complete evaluation by TEE is mandatory to confirm the optimal function of the THV (final position, presence, severity, and mechanisms of central or paravalvular leaks, transmitral gradients, and motion of leaflets) and to detect potential complications (acute migration, right-to-left interatrial shunt, LVOT obstruction, and tamponade).
9. A careful follow-up is required to detect delayed complications such as late valve displacement or migration, thrombosis, and dysfunction or structural deterioration. In the absence of any in-hospital adverse event, a predischarge evaluation with transthoracic echocardiography or TEE or multidetector computed tomography may be recommended to rule out early subclinical complications and serve as a reference for all subsequent evaluations.
10. Although transseptal TMVR is technically demanding, a comprehensive multidisciplinary screening process, optimal procedural planning, a strict step-by-step procedural approach, and a close follow-up of the patients will result in a high success rate and a reduced risk of complications.

Keywords: Anesthesia, General, Bioprosthesis, Cardiac Imaging Techniques, Cardiac Tamponade, Catheterization, Echocardiography, Echocardiography, Transesophageal, Heart Valve Diseases, Mitral Valve, Mitral Valve Annuloplasty, Multidetector Computed Tomography, Thrombosis, Transcatheter Aortic Valve Replacement, Vena Cava Filters

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