Transcatheter Mitral Valve Repair

Overview

TEER is a feasible and safe alternative to surgical MV replacement or repair in patients with high operative risk or contraindications for surgery. ^, Multiple TEER technologies have been developed addressing each component of the mitral apparatus thought to be responsible for the MV dysfunction ( Fig. 26.1 ). Each approach is tailored toward treating specific MV pathologies and regurgitation mechanisms. Transcatheter MV replacement has also become a reality. Accurate and detailed evaluation of MV morphology and function is critical for the success of these interventions. Echocardiography plays a pivotal role in patient selection, procedural guidance, and evaluation of immediate and long-term results. ^{, ,}

Historically, reoperation was the only recourse for a failing bioprosthetic valve. Today, percutaneous options exist with the use of transcatheter valve implantation. Determining candidacy for this less invasive valve-in-valve option requires careful evaluation with echocardiography. Transcatheter MV replacement and other novel approaches to TEER are being developed and are likely to expand the options to treat MV diseases percutaneously. ^, This chapter focuses on transcatheter repair using the edge-to-edge MitraClip technology ( Fig. 26.2 ). Much of the knowledge and experience gained in selecting patients, guiding the intervention, and assessing the result of edge-to-edge repair can be applied to newer technologies as they enter clinical practice.

TEER is the general approach, with MitraClip edge-to-edge repair representing the major commercially available technology. MitraClip has achieved approval by the US Food and Drug Administration and the European Union CE Mark. The most recent generation of the MitraClip device, the MitraClip G4, puts new enhancements into the hands of physicians by delivering an expanded range of clip sizes, an alternative leaflet grasping feature, and procedure assessment in real time for treatment of MV disease.

Edge-To-Edge Mitral Valve Repair

Of all available TEER procedures, the edge-to-edge MV repair has been used the most and has by far the largest number of treated patients. As of 2019, more than 80,000 patients had been treated with MitraClip therapy around the world. The first procedure was done in Venezuela in June 2003; this was quickly followed by the first procedure in the United States, which was performed on July 2, 2003, by Dr. Ted Feldman. The first procedure in Europe was performed on September 17, 2008, by Dr. Olaf Franzen. The use of TEER continues to expand, and a recent report highlights its potential application in nonagenarians. In addition, there is growing interest in combining mitral and tricuspid edge-to-edge repairs in patients with severe MR and tricuspid regurgitation and in using the MitraClip in the tricuspid valve for isolated severe tricuspid regurgitation.

Multiple US and international prospective clinical trials and registries ( Table 26.1 ) have demonstrated that in patients who are deemed to be at high risk for MV surgery, the percutaneous edge-to-edge mitral repair is feasible, safe, and effective in reducing mitral insufficiency, with resultant improvement of clinical symptoms, reduced frequency of hospitalizations for heart failure, improved quality of life, and significant left ventricular (LV) reverse remodeling. ^, Although the initial experience with the MitraClip was evaluated in primary MR, this has now been expanded to include patients with secondary mitral regurgitation. Echocardiography has played a central role in these trials. ^{, ,} Three-dimensional (3D) transesophageal echocardiography (TEE) has expanded our understanding of the effects of the MitraClip procedure on the shape and size of the mitral annulus. ^, The applicability and use of 3D TEE among the various imaging modalities for the assessment and guidance of therapy for MV disorders was reviewed in 2018.

Use of Echocardiography In Patient Selection

Patients likely to benefit from TEER have moderate to severe (3+) or severe (4+) primary MR, suitable MV morphology, and high to prohibitive surgical risk. The 2020 AHA/ACC Valve Guidelines continue to recommend mitral valve surgery, with surgical valve repair when possible for primary MR unless surgical risk is prohibitive. Two-dimensional (2D) transthoracic echocardiography (TTE) is recommended as the first-line imaging tool in MR and is often sufficient for diagnosis and characterization of the cause and severity of the MR. 2D TEE is used to better characterize mitral leaflet morphology and for guidance in preprocedural planning. 3D TEE provides realistic and intuitive anatomic images of the mitral leaflets and further aids in patient eligibility for TEER.

In addition to characterizing MV morphology and function, echocardiography is used for the quantitative assessment of LV diameters, volumes, and ejection fraction. The TTE 2D-based biplane method of disks is the recommended approach for the estimation of LV volumes and ejection fraction. The MitraClip is contraindicated in patients with active endocarditis, rheumatic MV disease, small MV annulus, and evidence of intracardiac thrombus; echocardiography aids in excluding all of these problems. MV characteristics that potentially decrease the chance of a successful MitraClip repair include dense calcification of the mitral annulus, MV clefts, excessive leaflet flail gap or width, and inappropriate leaflet coaptation depth and length ( Fig. 26.3 ). Finally, the location of the regurgitant jet or jets is best characterized by TEE and should be noted using the A1–A3/P1–P3 (Carpentier) nomenclature.

Determining the Cause of Mitral Regurgitation

Most of the studies dealing with TEER have adopted the classification of MR as primary (i.e., intrinsic valvular disease, called primary, organic, or structural MR) or secondary (i.e., without evident structural abnormalities of the MV, called secondary or nonstructural MR). Secondary MR develops despite a structurally normal MV in the context of ischemic heart disease or dilated cardiomyopathy.

The distinction between secondary and primary MR has practical implications related to TEER because there are specific echocardiographic exclusion criteria for each of these forms of MR (see Fig. 26.3 ), as well as mild differences in severity grading. An integrative clinical and echocardiographic approach to chronic MR, with a focus on the contrasts between primary and secondary MR, is essential for correct diagnosis, characterization, and management.

Primary Mitral Regurgitation

Primary MV disease is the most common cause of MR being treated with surgery and has been the main MV pathology in many studies of TEER. Several forms of primary MR exist and have been well characterized by echocardiography. ^, These include the spectrum from mild single-scallop MV prolapse (usually fibroelastic deficiency) to multiscallop severe prolapse (Barlow disease) and ruptured chordae with flail leaflet ( Fig. 26.4 ). Whereas the ideal TEER candidate will have central MR originating from prolapse affecting the A2-P2 scallops, the MitraClip can be implanted in patients with prolapse or flail of any of the scallops, with the caveat that potential Clip Delivery System entrapment in the chordae apparatus is increased.

Secondary Mitral Regurgitation

Unlike primary MR, for which repair therapy is clearly preferred, the optimal approach for secondary MR is still being defined. This has created growing interest in the potential application of TEER in patients with heart failure and secondary MR. Patients with both ischemic and non-ischemic secondary MR typically have structurally normal leaflets and mitral insufficiency due to poor leaflet coaptation ( Fig. 26.5 ), leaflet tethering, tenting, and mitral annular dilation. In some patients, the posterior leaflet remains in a semi-open position throughout the cardiac cycle (restricted leaflet motion), and the anterior leaflet appears to be prolapsing during systole. The systolic restriction of posterior leaflet motion seen in secondary MR should not be confused with that seen in carcinoid or lupus valve disease or, more commonly, with rheumatic MR, where, in addition to systolic and diastolic leaflet motion restriction, there usually is leaflet thickening (especially at the tips), chordal thickening, and the key component of rheumatic involvement, commissural fusion. The 2020 AHA/ACC Valve Guidelines for secondary MR indicate that TEER is reasonable in patients with a low LVEF (<50%) with persistent symptoms on optimal guideline-directed medical therapy when mitral valve anatomy is favorable, LVEF is between 20% and 50%, LV end systolic diameter is less than 70 mm, and pulmonary systolic pressure is less than 70 mmHg.

Mixed Mitral Regurgitation

Although the classification of secondary MR versus primary MR is well established and has helped in determining the appropriate therapeutic options, there exists a group of patients that can be better characterized as having mixed MR from a combination of primary and secondary causes. A good example would be a patient with MV prolapse who develops myocardial infarction ( Fig. 26.6 ) or LV dilation and dysfunction, adding a secondary component to the MR. An attempt should be made to characterize the predominant type of MR as primary or secondary.