Mitral Valve Repair

In order to describe the historical evolution of mitral valve repair, we must recognize that, in parallel with the development of new techniques, there has been a profound change in the cause of valvular heart disease in the Western world. In contrast with the almost universal prevalence of rheumatic lesions observed in the past (when “closed” mitral commissurotomy for rheumatic mitral stenosis was the mainstay of surgical treatment of acquired heart disease), now the great majority of surgery on the mitral valve is performed for insufficiency secondary to degenerative disease or, less often, secondary to ischemic disease.

The Past

Although the proposal that a surgical procedure could relieve the narrowing of the diseased rheumatic mitral valve had been put forward at the beginning of the 20th century¹ and then applied sporadically with success in the 1920s,^2,3 it was not until 1948 that surgical relief of mitral stenosis was definitively introduced in clinical practice, independently and simultaneously by Charles Bailey⁴ and Dwight Harken.⁵

Why it took 50 years for the surgical treatment of mitral stenosis to be accepted and established as a routine procedure has been a matter of speculation.⁶ The most probable explanation is that, until the second half of the 20th century, the attribution of the symptoms, signs, clinical picture, and natural history of mitral stenosis to the deformity of the valve⁷ was believed to be an erroneous idea. Consequently, surgical relief of the narrowing was widely held to be useless, and an unjustifiable operation.

Various new techniques were introduced at the advent of open-heart surgery. At first, these were aimed at the correction of mitral stenosis and, immediately thereafter, at the repair of mitral insufficiency. The procedures aimed at correcting insufficiency were initially designed to restrict the mitral annulus by means of sutures^8,9; subsequently, these were replaced by more advanced techniques, including the implantation of various types of annuloplasty rings,¹⁰ extensive leaflet resection, chordal shortening, and chordal transposition.¹¹ These techniques provided excellent long-term results when the disease was limited to the mural leaflet of the mitral valve, but they proved less satisfactory when the anterior leaflet was involved.

The Present

Two technical advances, one in cardiology and the other in surgery, have provided marked improvement in the conservative treatment of complex degenerative lesions of the mitral valve.

On the cardiologic side, advances in echocardiographic techniques have provided a better understanding of the geometric and functional characteristics of the mitral valve complex, including the identification of characteristic landmarks such as the triangle of coaptation, the length and depth of coaptation, and the coaptation point. Identification of these landmarks enables a detailed evaluation of normal and abnormal valve function and the definition of the mechanism of mitral regurgitation, thereby permitting competent and durable valve restoration by means of appropriate surgical intervention.

Furthermore, the introduction of transesophageal echocardiography has enabled detailed intraoperative evaluation of valvular dysfunction, including the immediate evaluation of repair results, so that corrections can be made if necessary.

The most important surgical innovation has been the introduction of expanded polytetrafluoroethylene sutures (ePTFE; GORE-TEX®; W.L. Gore & Associates, Inc.; Flagstaff, Ariz) as a replacement for elongated or ruptured native chordae tendineae.^12,13

The aim of the repair with artificial chordae is to restore the geometric and functional characteristics of the mitral valve complex by reconstructing the triangle of coaptation; this requires appropriate coaptation length and depth and positioning of the coaptation point well within the left ventricle (LV). Further, a competent and durable repair requires the preservation of leaflet mobility, permanent stabilization of the mitral annulus, and completeness of repair.

The crucial issue for the implementation of chordae replacement is accurate determination of the length of the artificial chordae, especially when both leaflets are prolapsing, because in such cases native chordal length lacks a fixed anatomic reference point. To overcome these difficulties, surgeons have used empirical or objective criteria to determine the appropriate length of the artificial chordae.

The empirical method is to adjust the length of the chordae under direct vision while continuously testing the coaptation of the leaflet by filling the ventricle with saline before definitively tying the knot.^13–15 The objective technique consists, in general, of predetermining the length of the artificial chordae by means of preoperative echocardiographic evaluation^16,17 of the beating heart; direct observation of leaflet coaptation is limited to filling the LV with saline solution only when performing final intraoperative evaluation of the correction.¹⁸

Our Experience. On the basis of our 10-year experience with 549 patients with bileaflet prolapse, we have developed the following technique. First, we determine neochordal length by accurate echocardiographic measurement of the prolapse of each scallop, taking as a reference point the theoretical point of coaptation that, again on the basis of our extensive observation, we recognize to be approximately 4 mm below the mitral annular plane.¹⁹

The length of the individual artificial chordae is measured against the length of the elongated native chordae. The artificial chordae have to be shorter than the native chordae as measured from the edge of the prolapsing scallop to the theoretical point of coaptation measured echocardiographically. Using this technique, we have attained favorable long-term results in over 95% of our cases.²⁰

Current surgical repair of mitral valve degenerative disease offers a wide armamentarium of approaches. The successful surgical repair rate exceeds 90%, even in complex cases of anterior or bileaflet mitral prolapse, with long-term survival and freedom from reoperation rates that are comparable to those associated with the correction of isolated posterior leaflet prolapse.

In the continuing quest for reduced surgical trauma—with decreased occurrence of respiratory failure, decreased postoperative pain, shorter intensive-care-unit stay, faster recovery, and better cosmetic results—repair of the mitral valve is more often being performed through minimally invasive techniques that range from minithoracotomies to totally robot-assisted procedures.

In our own experience, a growing percentage of patients with mitral insufficiency undergo valve repair through a right minithoracotomy which, in our series, represents 14% of the total number of procedures.²⁰

What Lies Ahead

Various methods that use transcatheter approaches to mitral valve repair—without cardiopulmonary bypass —are currently in various stages of clinical application, while others are still in an experimental stage.

Some of these innovative procedures act directly on the valve leaflets, others attempt to restrict the mitral annulus, and still others attempt to modify LV shape; recently, clinical implantation of mitral valve prostheses has been performed per catheter in a very few selected cases.

Among the procedures that act directly on the valve leaflets, the one with the largest number of clinical implantations is the percutaneous mitral leaflet repair with the MitraClip Mitral Valve Repair System (Abbott Vascular, part of Abbott Laboratories; Santa Clara, Calif), which is introduced transseptally via peripheral vein access. The MitraClip enables grasping and approximating the anterior and posterior mitral leaflets, thus creating a double mitral valve orifice that replicates the edge-to-edge technique for the repair of mitral valve insufficiency.

Another approach that aims to act directly on the valve leaflets is the off-pump, echo-guided transapical implantation of artificial chordae that are secured outside the LV and fastened to the prolapsing mitral leaflet (Mobius II, Edwards Lifesciences LLC; Irvine, Calif). However, this device has been abandoned after having been applied unsuccessfully in a few cases. There is also the investigational NeoChord DS1000 (NeoChord, Inc.; Eden Prairie, Minn), a device that has proved effective in reducing mitral regurgitation in the experimental setting^21,22 but so far has shown very limited clinical applications.

When mitral leaflets that display normal leaflet motion fail to coapt (secondary to ventricular dilation or ischemic posterior papillary muscle and posterior-wall dysfunction), one can attempt to treat this dysfunction percutaneously by restricting the mitral annulus. Techniques that use this principle have attained clinical application by introducing a constraining device in the coronary sinus to partially encircle the mitral valve annulus in order to restore mitral geometry.²³ The most successful device using this approach is the Carillon® Mitral Contour System™ (Cardiac Dimensions, Inc.; Kirkland, Wash).

Other transcatheter devices under development in order to achieve mitral annuloplasty have already been applied clinically, in selected cases. Among these are the QuantumCor (QuantumCor Inc.; Bothell, Wash), which involves radiofrequency-based thermal remodeling of mitral annular collagen, and the investigational GDS Accucinch® System (Guided Delivery Systems Inc.; Santa Clara, Calif), in which several anchoring devices are placed in the ventricular aspect below the posterior mitral leaflet, via a retrograde femoral approach under fluoroscopic and echocardiographic guidance.

Research aimed at applying percutaneous techniques to the improvement of leaflet coaptation by decreasing mitral annular diameter through a modification of the geometry of the LV has been attempted without success and has been largely abandoned. For example, the iCoapsys System (Edwards Lifesciences LLC; Irvine, Calif) attempted to modify LV shape by applying tension to a device tethered to the ventricular wall; and the Septal Shortening System (PS3 System) (Ample Medical, Inc.; Foster City, Calif) applied tension to a bridge that connected the interatrial septum with the coronary sinus.²⁴

Mention must be made of the most radical innovative transcatheter procedure, still in the experimental stage, in which a stented prosthetic mitral valve is implanted in its anatomic position. Transcatheter mitral valve implantation has been described in experimental animal models. Two delivery systems have been developed: the retrograde transapical approach²⁵ and the transvenous, transseptal antegrade approach.²⁶ In this decade, these techniques have been successfully adopted in a small number of patients in order to treat degenerated tissue prostheses^27,28 or failed mitral repairs in which annuloplasty rings had been implanted.²⁹

Initial experiences of transcatheter valved stent implantation directly in the native mitral annulus have also been recently reported. In one case, the intervention was partially aided by a traditional surgical approach.³⁰ Furthermore, a bioprosthetic valve (CardiAQ Valve Technologies, Inc.; Winchester, Mass) was implanted in the native mitral annulus by means of a transcatheter approach.³¹

The positive results obtained with transcatheter aortic valve implantation procedures have stimulated the perception that transcatheter mitral valve repair can be achieved with relative ease. It must be underscored, however, that the mitral valve is a highly complex structure whose function is dependent upon the harmonious interaction of 5 different components: the annulus, the leaflets, the chordae tendinae, the papillary muscles, and the LV. Because degenerative mitral valve disease often implicates all these components to various degrees, surgical experience has repeatedly shown that successful and durable mitral valve repair must be grounded both in accurate and complete anatomic correction and in the re-establishment of physiologically normal valvular function. Therefore, effective repair must encompass all the components of the mitral valve complex involved by the disease.

At the present time, the main limitation of a transcatheter approach to correct mitral insufficiency is the fact that even the most advanced devices are capable of correcting only a single defective component of valve disease: the leaflets, the annulus, or the ventricular shape.

Unless future technological development produces devices capable of acting simultaneously on several diseased components of the mitral valve, uncertainty exists in contemplating if, how, and when transcatheter mitral valve repair will become a routine clinical procedure. Conversely, because of their minimal invasiveness, transcatheter device procedures might find an elective application as a palliative treatment limited to a selected population of patients with multiple comorbidities.

A more promising outlook is offered by the transcatheter valve-in-valve and valve-in-annuloplasty ring implants for the treatment of degenerated tissue prostheses and failed annuloplasty, respectively, because these devices present the distinct advantage of enabling prosthetic valve replacement while avoiding standard mitral valve reoperation with its attendant risk of death and morbidity.