Mitral regurgitation is the second most common type of heart valve disease in Europe and the most common type of heart valve insufficiency in the United States. Approximately 50,000 of these patients require surgical intervention each year in the United States. The incidence of mitral regurgitation is predicted to increase due to greater longevity with more degenerative and functional valve disease and patients with congestive heart failure.
The quest for a percutaneous approach is continuous despite the established feasibility, safety and results of conventional and minimally invasive surgical procedures. Emerging transcatheter techniques offer an alternative approach f patients considered high risk or contraindicated for conventional surgery. Transcatheter aortic valve implantation has already showed established feasibility in patients with severe symptomatic aortic stenosis.
Transcatheter procedures and conventional surgery alike offer techniques for mitral valve repair and percutaneous mitral valve replacement. Attempts to repair the valve have approached the problem via three distinct routes*:
- Leaflet repair
- Annuloplasty : directly or indirectly via the coronary sinus
- Ventricular modeling
1. Leaflet repair
This approach attempts leaflet repair by a reproduction of the edge to edge repair initially described by Alfieri . The principle is to place a suture between the leaflets to create a double orifice mitral valve by co-apting the central leaflet scallops (figure 1). In the percutaneous procedure, a guide catheter is inserted from the right femoral vein into the left atrium through a trans-septal approach. A delivery system with a clip (MitraClip®, Evalve Inc., Menlo Park, USA) (figure 2) is steered through the mitral valve and positioned under echocardiographic and fluoroscopic control until a successful result as shown by diminished mitral regurgitation is obtained. A second clip can be placed if necessary. The MitraClip® has been evaluated with the Endovascular Valve Edge-to-Edge Repair Study (EVEREST) I which demonstrated safety and feasibility. The ongoing EVEREST II trial compares the MitraClip device with standard surgical repair or replacement. Available results,4,5 report a 85% acute procedural success, defined as a successful clip implantation with core echocardiographic laboratory assessment of MR <2+ at discharge.
Remodeling of the mitral valve by surgical mitral annuloplasty is the current standard repair technique for functional mitral regurgitation. The procedure is based on the principle of correction of leaflet coaptation by decreasing the size of the annulus.
It has been performed with transcatheter techniques with devices introduced into the coronary sinus to reproduce the same effect; this has been termed“indirect annuloplasty”. It has been proposed mainly for patients with functional mitral regurgitation due to left ventricular dilatation or ischaemic papillary muscle and posterior wall dysfunction for whom surgery is not a feasible option.
Several devices are available, as the Viacor percutaneous transvenous mitral annuloplasty (Viacor, Wilmington, Massachusetts, USA), CARILLON mitral contour system (Cardiac Dimensions, Kirkland, Washington, USA) and MONARC percutaneous transvenous mitral annuloplasty system (Edwards Lifesciences). The overall principal of these devices is based on a reshaping of the coronary sinus by shafts of different shapes and curves anchored proximally and distally in the coronary sinus (figure 3). Post deployment tension is applied to cinch the sinus and mitral annulus. Despite encouraging animal and preliminary human studies, there are several queries related to the real anatomical safety and applicability of this approach. Direct annuloplasty has been attempted with transcatheter techniques that emulate suture mitral annuloplasty surgery. The goal is to provide direct geometric reduction of the posterior annulus. Several systems are available such as the Mitralign Percutaneous Annuloplasty System (TM) (Mitralign, Inc. Tewksbury, MA, USA). The QuantumCor radio-frequency ablation system (QuantumCor, Lake Forest, CA, USA) attempts to reduce the annulus size of mitral valve annulus by application of radio-frequency.
3. Ventricular modeling
The principle of these systems is to reduce mitral regurgitation by reducing the antero-posterior mitral annular diameter, re-approximating the anterior and posterior mitral valve leaflets and reducing functional mitral regurgitation. Technically speaking, they are not transcatheter devices but can be employed without the need for extracorporeal circulation. The Myocor iCoapsys (Myocor Inc., Maple Grove, MN) has been discontinued.
Figure 1. The edge-to-edge repair described by Prof. Ottavio Alfieri, transforming the mitral valve into a double orifice mitral valve by co-apting the central leaflet scallops
Figure 2. The MitraClip system, consisting of V-shaped clip which is affixed to the anterior and posterior mitral leaflets
Figure 3. Cross section of the heart at the level of the atrioventricular valves. The blue line shows the site of implantation of coronary sinus devices.
Mitral valve repair with transcatheter techniques on a beating heart is feasible and can be effective. Approaches include direct leaflet modification, annuloplasty directly or indirectly using the coronary sinus, and ventricular geometric modification. Careful patient selection and a multidisciplinary approach are pivotal for its success and imaging techniques play a cornerstone role in the application of these procedures. Many of these devices are still in the investigational stages of development. Advances in the technology will surely improve efficacy and simplify the procedure. Disclosure of interest: The author has no conflict of interests.
* The list of devices cited in this article is not exhaustive and is only intended for illustrative purposes.