Aortic annuloplasty ring: coronet or flat or not or what?

Abstract

The anatomy and physiology of the aortic valve is ingenious, complex and greatly unknown, particularly its relationship to the left ventricular outflow tract and the ascending aorta. Sophisticated studies have shown that all parts of the aortic valve and the adjacent anatomic structures play together in a finely tuned concert during the cardiac cycle [1], allowing for optimal performance in every aspect, e.g. stress reduction of cusps, adaptation to varying flow conditions, optimizing function of the circulation and also the left ventricle. Theoretically, repair of the regurgitant aortic valve offers the advantage of preserving autologous, orthotopic living tissue, ideal for long-term function, especially when the pathological process is functional in origin and less tissue-related. However, a repaired valve remains a repaired valve. We cannot yet achieve the conditions of a normal valve concerning the function and durability that must be known by the surgeon and the patients. Nevertheless, results in specialized centres are promising for the first postoperative decade [2], but widespread acceptance of aortic valve repair is reserved. One of the reasons is the low level of standardization of repair procedures, particularly when an enlarged annulus is involved in the disease. This again starts with the problem of the terminology of the annulus [3] and the question ‘when is an annulus enlarged in relation to the geometry of the cusps?’, a relationship that is seldom normal and quite different in the different aortic valve pathologies. Rankin et al .[ 4] present, in this issue, a possible solution to this problem, namely the implantation of an aortic annuloplasty ring showing excellent results in animals with normal cusp geometry. This annuloplasty ring has an elliptical base geometry and subcommissural posts, giving a crown-shaped appearance. The design is based on the normal human aortic valve and intends to reconstruct the whole aortic valve functional unit [5] from base to commissures. The similarity of the shape of this aortic annuloplasty ring to the normal valve implies that ideally the cusps of the valve to be repaired should also have normal geometry, which is not always the case. In bicuspid aortic valves, commissures are either absent or underdeveloped [6], and the annulus is often asymmetrically dilated and deeper at the aorto-mitral junction, rendering the adaptation of this annuloplasty ring to the bicuspid valve configuration not ideal. Also, the often significantly elongated commissure between the right and non-coronary sinus in Marfan patients may present a difficult anatomic situation for this type of ring. Functional aortic valve insufficiency due to root dilatation, which is one possible indication for that ring, is nowadays repaired by valve-sparing procedures with excellent results, including the advantage of resecting the aneurysmal sinus tissue and allowing for adaptation to valve asymmetry [7]. Of concern is the fact that the coronet-shaped annuloplasty ring may come into cyclic contact with the cusps potentially causing abrasion of cusp tissue especially at the commissures with a long-term risk of cusp deterioration. This problem seems to be avoided by a special implantation technique, as studied in very short-term, 2-month animal trials [4]. Applied to the mitral situation a flat annuloplasty ring remodelling the annulus at the base only may be an alternative to bring together the three sinuses and the corresponding