Extensive calcification of the mitral valve annulus is a pathological entity that may or may not be associated with other mitral valve diseases. In its most characteristic configuration, it forms a semilunar deposit of calcium within the posterior annulus with limited extension to the leaflet tissue. This process differs from calcification in rheumatic valve disease, which usually involves the commissures and the leaflet tissue with only late extension to the annulus.
Mitral annular calcification can be observed in two different circumstances depending upon the presence or absence of a preexisting primary valve pathology. Annular calcification without preexisting mitral disease is seen most frequently in the elderly and in patients with systemic hypertension or metabolic disorders (e.g., diabetes, hyperparathyroidism, chronic renal failure). These patients are usually asymptomatic with the exception of rare cases of significant mitral valve stenosis. In most instances the diagnosis is made by x-ray, echocardiography ( Fig. 27-1, a ), or cardiac catheterization ( Fig. 27-1, b ) during a systematic clinical examination.
Annular calcification may also develop in situations of a preexisting mitral valve disease such as fibroelastic deficiency in older patients or Barlow’s, Marfan, or Hurler’s syndrome in younger patients.
PATHOPHYSIOLOGY
The calcification process typically involves the posterior annulus with variable degrees of extension ( Fig. 27-2 ). The calcification process is limited to the annulus in most patients (a) but may extend to the leaflet tissue, the ventricular myocardium, and/or the papillary muscles (b) . Calcium formation is encapsulated into a fibrous sheath distinct from the surrounding tissues except in areas of myocardial infiltration. In most instances the annular calcium formation can be removed en bloc by dissecting the fibrous sheath from the surrounding tissues.
The pathogenesis of mitral annular calcification remains unknown. We believe that mechanical constraints on the atrio-valvular junction play a major role in this process ( Table 27-1 ). In our experience, we have consistently noticed that the calcification correlates with the presence of annular fissures and cracks that are found at the base of leaflets with excess tissue ( Fig. 27-2, a ). These radial fissures or dehiscences likely result from excess tension at the atrio-valvular junction, a consequence of Laplace’s law. These defects are saturated with lipoid substances, protein deposits, and platelet aggregates that initiate the process of calcification as demonstrated by punctuate lesions of early mineralization. Besides mechanical factors, biochemical factors also play a role in the process. Histochemical studies have shown that proteoglycans and collagen are severely altered in degenerative valvular disease. The resulting disorientation of the collagen fibers and the increased tissue weakness initiate a vicious cycle that leads to annular dehiscence and the different stages of calcification.
Mitral annular calcification may contribute to the onset of mitral valve regurgitation as a result of increasing tension on the subvalvular apparatus leading to chordae elongation and/or rupture. Only when the regurgitation becomes severe should surgery be undertaken.
SURGICAL MANAGEMENT
The management of annular calcification is a surgical challenge. Several surgical techniques of valve replacement have been published, with mixed results. Passing sutures through the calcium bar to secure the prosthesis is difficult, and although it is usually possible it carries a risk of calcium fragmentation, annular dehiscence, atrio-ventricular dissociation, or perivalvular leak. The technique of en bloc excision of the calcium bar and subsequent valve reconstruction was developed to minimize these potential complications. The surgical management has been extensively described in Chapter 9 . It is based on the following principles: annular decalcification by en bloc resection rather than calcium fragmentation, and reconstruction of the annulus using living tissue.
Annular Decalcification
In the typical setting of calcification of the posterior annulus, the base of the posterior leaflet is detached from the calcium block and retracted. This provides extensive exposure of the calcified annulus. Decalcification is initiated by incising the endocardium around the atrial and ventricular borders of the calcified bar using sharp dissection. The tip of the blade should be oriented such that the surrounding tissue is separated from the calcium bar. Preserving the fibrous sheath encapsulating the calcium bar allows an en bloc resection without calcium fragmentation ( Fig. 27-3 ). The dissection is performed by developing a circumferential plane from one extremity of the calcium bar towards the other until the entire length of the block is removed. The removal of the bar exposes the atrio-ventricular connective tissue and fat, which contain and protect the circumflex artery and the coronary sinus.
Annular Reconstruction
In most instances, the calcification process is limited to the annulus, and the en bloc decalcification leaves two edges of fibrous sheath delineating the atrium superiorly and the ventricle inferiorly. The atrio-valvular junction is reconstructed by a series of “2/0-figure-of-eight-mattress” braided sutures placed through the atrial and ventricular edges extensively described in Fig. 9-4 . The ventricular bites are oriented along the longitudinal axis of the ventricle to preserve myocardial vascularization. These sutures should involve one third of the thickness of the myocardial wall and be 1 cm wide, taking advantage of any fibrous tissue identified at the surface of the endocardium. To prevent myocardial ischemia caused by possible compression of the myocardium by the pledgets, use of pledgetted mattress sutures should be avoided. Exerting traction on the “figure-of-eight-mattress” sutures, while displacing downward the atrial edge with forceps, reduces the size of the annulus and closes the atrioventricular groove, displacing the connective vessels and surrounding fat away from the reconstructed annulus. The two ends of the “figure-of-eight mattress” sutures are set aside to secure the ring at a later stage. A continuous 4-0 polyester suture is used to further approximate the atrioventricular junction and to prevent its dissection by infiltration of blood. Using this technique, the atrio-valvular junction is restored as a living structure.
Valve Reconstruction
In circumstances where annular calcification is the only lesion, the posterior leaflet can be reattached to the reconstructed annulus following the previously described procedure. When the posterior leaflet is prolapsed, standard techniques are used, including triangular or quadrangular resection. In the case of anterior leaflet and/or commissural prolapse, which requires a technique involving the papillary muscle, the repair should precede posterior leaflet reconstruction. After the leaflet reconstruction is completed, simple horizontal sutures are placed. A properly sized prosthetic ring is then inserted using these sutures and the “figure-of-eight-mattress” sutures. The latter sutures must be tied with gentle traction on both ends to set appropriate tension on the intermediate loops.
The “Sliding Atrium Technique”
Whenever calcium extends to the ventricular myocardium the en bloc removal of the calcium bar leaves a large area of myocardium without fibrous tissue coverage (see Fig. 9-5 ). The atrial edge is dissected to mobilize an atrial flap, which is used to cover the exposed area of myocardium. The fat and connective tissue surrounding the circumflex artery and coronary sinus are left attached to the ventricular side.
“Figure-of-eight-mattress” 2-0 braided sutures are used as described previously, with large vertical ventricular bites that take advantage of any fibrous tissue covering the ventricular endocardium. While gentle traction is applied to these sutures, the atrial flap is displaced downward with forceps to cover the area of exposed myocardium. An additional 4-0 running suture is used to secure the fixation of the atrial flap edge.
Management of Calcified Papillary Muscle
The heads of one or several papillary muscles may be calcified, in addition to the annulus. The calcification may or may not extend to the chordae. Intact chordae can be separated and reattached to an adjacent noncalcified papillary muscle head. Whenever several marginal chordae require resection, chordae transposition or artificial chordae may be used. In cases of extensive calcification of a papillary muscle and adjacent chordae, valve replacement is indicated.
The technique of en bloc decalcification and annular reconstruction can also be used in cases with complex annular calcification that require valve replacement.
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