Details of anatomical and physiological changes in secondary mitral valve regurgitation are extensively addressed in Chaps.​ 2 and 3. An understanding of these fundamental changes can help tailor the appropriate mitral valve repair techniques and ideal prosthetic device selection.

Left ventricular remodeling, chamber dilatation, impaired contractility, and mitral annular enlargement with normal leaflet structure cause secondary mitral valve regurgitation. Treatment of this disease process with annuloplasty is based on overcoming leaflet tethering by correcting annular dilatation and deformation. Leaflet tethering is largely caused by a lateral displacement of both papillary muscles due to left ventricular dilatation. Annuloplasty deals with the circumferential (both anterior and posterior) annular dilatation seen in functional mitral regurgitation [5]. However, it has been noted that the annular dilatation is often not severe in secondary mitral regurgitation, especially where ischemic etiology is the cause [6]. The success of annuloplasty therefore rests primarily on the degree to which it can reduce the restrictive leaflet tethering and allow better leaflet coaptation. Correction of annular dilatation alone may not eliminate mitral regurgitation as the tethered leaflets can still mal-coapt below the annular plane. To specifically address the leaflet tethering, annuloplasty should also ‘over-correct’ the septolateral displacement thereby reducing the tethering distance [5]. This forces the tethered leaflet(s) to coapt better in systole by displacing the anterior leaflet towards the severely restricted posterior leaflet in a valve orifice that is relatively small compared to the length of the anterior leaflet. Downsized rings and specially shaped rings work to achieve a more ideal depth of coaptation. A similar effect can be achieved by leaflet patch augmentation with a normal sized annuloplasty ring. In leaflet augmentation there is a larger coaptation surface relative to the size of the ring orifice [7].

Asymmetric dilatation of the mitral annulus can also cause dysfunction in leaflet coaptation. The anterior annulus is formed by the fibrous skeleton of the heart and is found to be less distensible compared to the posterior annulus. Alterations in ventricular dimensions can account for the asymmetric annular dilatation affecting the posterior annulus. These annular changes alter the normal annular shape, which is roughly round during diastole and kidney shape during systole. In functional regurgitation the annulus becomes circular and also loses its saddle in systole [5]. It was once believed that the intertrigonal distance was not affected by the changes in cardiac chamber dimensions due to the fibrous skeleton. Heub and colleagues examined pathologic specimens to disprove this belief by showing the anterior annulus can dilate substantially in functional MR [8, 9]. This becomes a very important concept in sizing of annuloplasty rings. The majority of ring annuloplasty systems attempt to restore the normal annular shape in systole along with maintaining the saddle-shape in which the highest points lie anteriorly and posteriorly. These systems stabilize the dilatation in the typical systolic kidney shape which helps avoid further dilatation [10, 11]. Some annuloplasty systems have more complex or asymmetrical shaping to accommodate regional tethering or to further over-correct the septolateral dimension.

With the introduction of the bubble oxygenator in the 1950s, the field of open mitral valve repair was born. Many groups devised different techniques to restore the dilated annulus to improve leaflet coaptation and reduced mitral insufficiency. Davila and colleagues introduced a method of a circumferential suture to reduce the annulus, while others such as Scott, Lellehei, and Nichols used varying techniques to reduce the orifice to allow a reduction of regurgitation [12, 13]. In 1960, Kay and colleagues introduced the use of Teflon or Ivalon to bolster the running or interrupted suture annuloplasty to prevent pulling through of sutures when under tension [14, 15].

The concept of mitral annuloplasty was first introduced in the literature by Lillehei and associates in 1957. Subsequently, in 1968 Carpentier implanted the first prosthetic ring, the Carpentier Classic ring, as a rigid structure that was size matched to the anterior leaflet to stabilize the dilated annulus. It was primarily designed for rheumatic valvular disease, as this was the predominant cause of mitral regurgitation at that time [10, 16, 17]. It allowed the appropriate rigidity for the fibrotic annuli seen in rheumatic valves. Duran and colleagues noted changes in shape of the mitral annulus during the cardiac cycle, which lead them to implant a flexible ring to prevent ventricular dysfunction hypothesized by rigid rings [10]. Since that time, a multitude of prosthetic ring annuloplasty systems have been introduced. These include complete rings as well as band devices, which are traditionally sewn to the posterior annulus to address annular dilatation in this location. There are rigid, semi rigid and flexible devices some of which are disease specific due to anterior-posterior shape as well as planar geometry.

An abundance of prosthetic materials and techniques have been used to reduce the septolateral diameter in functional mitral regurgitation. Regardless of the type of annuloplasty, or the cause of regurgitation, it remains integral to address annular pathology when repairing the regurgitant mitral valve [18]. Of the common techniques, most groups have abandoned suture annuloplasty in favor of the ring annuloplasty because of inferior results and more difficult reproducibility with the former [19]. Few surgeons have, however, persisted with the suture technique, but mostly for primary rather than secondary regurgitation [20]. Most surgeons rely on prosthetic bands or rings for annular support. These annuloplasty devices can be rigid or flexible, complete or incomplete, and made by multiple different materials.

As with most aspects of mitral valve repair, the optimal prosthesis has not been identified. As described earlier, many different materials have been used to achieve an adequate annular plication including suture, pericardium, Dacron or vascular grafts along with a multitude of manufactured prosthetic rings and bands [21]. The ideal prosthetic device would allow the optimal hemodynamics in terms of left ventricular function and dimension, along with minimal risk of causing mitral stenosis or systolic anterior motion. Ease of implantation and cost are also relevant factors to consider. Despite at least three randomized trials attempting to compare different devices and many different variations in devices, there has been no consensus as to the best device to restore mitral annular dimensions for most pathology [22–24].

Annuloplasty for secondary mitral regurgitation differs notably from that for primary mitral regurgitation. As described previously, in most cases of secondary mitral regurgitation, the annuloplasty is the only technique employed to achieve adequate leaflet coaptation. The most difficult and often less predictable aspect of the annuloplasty is maintaining long-term leaflet coaptation, and, therefore, freedom from regurgitation. Recurrent mitral regurgitation is often due to persistence or progression of LV remodeling. The ability to maintain permanent reduction of the septolateral dimension is imperative to annuloplasty in functional regurgitation as this will protect to some degree from continued tethering if the ventricle remodels further. Though appropriate patient selection and addressing ventricular remodeling when necessary are key factors for a successful repair, the annuloplasty remains paramount in achieving ideal long-term results [25].