Calcified Annular Disease

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.

TABLE 27-1

Proposed Mechanism of Mitral Valve Annular 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.