The most important functional characteristic of type IIIb dysfunction, compared to type IIIa, is a pure systolic restricted leaflet motion with preserved leaflet pliability. The most common causes of this dysfunction are ischemic myocardial disease, idiopathic dilated cardiomyopathy, and end-stage heart disease from other causes. The functional “trait commun” *
* See Glossary .
of these different etiologies is the tethering of the mitral valve leaflets during systole ( Fig. 14-1 ) caused either by segmental ventricular dilatation with asymmetrical valve tethering (a) or by global ventricular dilatation with symmetrical valve tethering (b) .
SEGMENTAL VENTRICULAR DILATATION
In the past, the fundamental mechanism of type IIIb dysfunction seen in ischemic valve disease was thought to be a papillary muscle dysfunction. Experimental studies in our laboratory in the 1980s showed that papillary muscle dysfunction produced by injecting formaldehyde in the posterior papillary muscle alone did not cause significant mitral valve regurgitation. To obtain regurgitation, it was necessary to inject formaldehyde also in the myocardial wall supporting this papillary muscle. Segmental ventricular dilatation is commonly seen in ischemic heart disease, resulting in asymmetrical apical and lateral displacement of one papillary muscle and tethering of the corresponding leaflet segments. The posteromedial papillary muscle is most frequently involved in ischemic mitral valve regurgitation. It produces a systolic restricted leaflet motion of the corresponding P2, P3, and PC segments and to some extent the A3 segment. In addition to asymmetrical leaflet tethering, the annulus fibrosus is asymmetrically dilated, involving predominantly the P2, P3, and PC regions ( Fig. 14-2, a ) . Leaflet tethering may also create a differential tension on the secondary chordae of the anterior leaflet that may distort the belly of this leaflet, producing what we described as an “effet de mouette” * deformity often seen on echocardiography ( b ).
The leaflet tissue usually has a normal appearance in type IIIb mitral regurgitation. However, it may present secondary lesions as a result of long-lasting valve dysfunction.
Several techniques have been developed to correct type IIIb regurgitation in ischemic mitral valve disease, the most important being annular remodeling using ring annuloplasty.
Annular Remodeling
Although the left atrium may be small in type IIIb mitral regurgitation, adequate exposure of the mitral valve can be obtained as described in Chapter 7 .
The most practical “angle d’attaque” * to treat type IIIb dysfunction is at the valvular level where the main anomalies are annular dilatation and valve tethering. An undersized remodeling ring annuloplasty can restore leaflet coaptation without the risk of stenosis because the leaflet tissue is pliable. Since leaflet tethering limits functional valvular tissue, an overcorrection of the annulus dimensions is necessary to ensure an adequate surface of coaptation.
The selection of the ring depends upon whether the annular dilatation is symmetrical or asymmetrical. In all circumstances, however, the method of sizing is identical and based on the measurement of the surface area of the anterior leaflet ( Fig. 14-3 ).
Since the annular deformation is usually asymmetrical, the use of an IMR ring, specially designed for this condition ( Chapter 8 ), is preferable. This ring has an asymmetrical design (a < b) to compensate for the leaflet tethering commonly seen in the P3 segment and the adjacent P2 and PC segments. The IMR ring does not need to be downsized because its dimensions have been altered to ensure an optimal surface of coaptation on the basis of the measurement of the anterior leaflet. The size of the selected ring is therefore the size indicated by the sizer covering the surface area of the anterior leaflet. As an alternative, a Classic ring or a Physio ring can be used, undersizing one or two sizes depending upon the degree of leaflet tethering. For example, if a 28-mm sizer fits the anterior leaflet, a 28-mm IMR ring size is implanted. Alternatively, a size 24-mm Physio or Classic ring could be used.
Ring Implantation
The technique of ring implantation ( Fig. 14-4 ) is described in Chapter 8 . However, important recommendations should be made because an aggressive downsizing may increase the risk of ring dehiscence resulting from the excess tension applied on the annular sutures. Care should be taken to ensure that the sutures are passed large and deep enough within the annulus (a) . Also advisable is the use of overlapping sutures or a double row of mattress sutures in the most dilated areas (b) . Finally, in the setting of asymmetrical dilatation, for proper positioning of the ring, particular attention should be paid to ensure that the middle of the posterior segment of the ring corresponds to the middle of the P2 segment (c, d) .
GLOBAL VENTRICULAR DILATATION
Global ventricular dilatation , seen in dilated cardiomyopathy, produces symmetrical displacement of the papillary muscles, tethering of all leaflet segments, and symmetrical dilatation of the annulus. The dilatation involves predominantly the posterior annulus but intercommissural distension also occurs in patients with type IIIb dysfunction.
Global annular dilatation can be treated at the annular level by a complete remodeling of the annulus ( Fig. 14-5 ). Since the annular dilatation is usually symmetrical, a Classic ring or a Physio ring should be used. Depending upon the degree of valve tethering, the size of the selected ring is downsized one or two sizes. The aggressive downsizing that is required to restore leaflet apposition increases the risk of ring dehiscence, caused by excess tension on the sutures. The special precautions previously described for asymmetrical dilatation should also be respected in the setting of global dilatation with the difference that overlapping sutures, or a double row fixation, should involve the whole circumference of the annulus.
