Correspondence Address:
A Kalangos
Head of the Clinic for Cardiovascular Surgery, University Hospital of Geneva, Geneva
Switzerland

Full Text

Thanks to Carpentier's efforts since 1970, mitral valve repair has become a well- established procedure with obvious advantages over valve replacement. A variety of reparative techniques were first described and applied by Carpentier who carefully analyzed the different physiopathological causes of mitral valve dysfunction in various spectrum of lesions. His pathophysiological classification of valvular dysfunction as type I (normal leaflet motion), type II (prolapsed leaflet), and type III (restricted leaflet motion), as well as his per-operative assessment of these lesions prior to valve repair allowed him to develop specific reparative techniques for each of these three types of mitral valve dysfunction. After 30 years of experience, these techniques have become reproducible and reliable. Long term results are stable in many cardiac surgery centers in the world, with feasibilty rates varying between 90 to 97% for degenerative mitral valve disease, 50 to 60% for rheumatic involvement, and 50 to 55% for ischemic disease.

However, the predictability of successful mitral valve repair, demonstrated by the incidence of early reoperation related to technical error or intraoperative misjudgment, varies from one surgeon to another, according to the degree of surgical experience in mitral valve repair. The most common cause for reoperation is residual prolapse, particularly that of the anterior leaflet, which is either not recognized or underestimated during surgery. About 70% of type II lesions are located on the posterior leaflet, and more specifically, on its median segment. Surgical correction of this type of prolapse - classical quadrangular resection and plication of the annulus - constitutes the most widespread mitral valve repair technique for which surgeons are easily trained to perform. On the other hand, correction of the anterior leaflet prolapse is undoubtedly technically demanding and complex, because the learning curve for the techniques performed at the level of the subvalvular apparatus, such as chordal shortening , sliding plasty of the papillary muscle, or shortening of papillary muscle is much longer and hence surgeon-dependent.

This is the main reason that some surgeons exerted their ingenuity and creativity to simplify the surgical correction of anterior leaflet prolapse by introducing the use of PTFE suture material to substitute chordae and the edge-to-edge technique described by Alfieri in this issue of the Journal.

The latter technique consists simply of anchoring the free edge of the prolapsing portion of the anterior leaflet to the facing edge of the non-prolapsing posterior leaflet. This correction results in a double mitral valve orifice when the prolapse is in the middle of the leaflet and in a smaller valve orifice when it is close to a commissure. The satisfactory preliminary results in the first series using the edge-to-edge technique, permitted its extensive use in unfavorable lesions - which constitute less than one-third of the global population of patients with severe isolated mitral regurgitation - such as prolapse of the anterior leaflet, prolapse of the posterior leaflet with a calcified posterior annulus, prolapse of both leaflets, prolapse in the commissural area, and regurgitation secondary to restricted leaflet motion or to endocarditic lesions.

The technique proved to be extremely reproducible as demonstrated by short cross-clamp times and by its efficacy even in cases of suboptimal peri-operative exposure and in cases of poorly understood mechanisms of mitral regurgitation as well as by the low incidence of reoperation directly related to this technique. Although the edge-to-edge technique appears to be a simple and effective solution for all the above-mentioned unfavorable conditions, some concerns remain regarding the reduction of the effective mitral orifice area resulting from the creation of a double orifice. The greatest reduction is observed when the stitch is placed exactly in the middle of the valve, the expected reduction being more than 60% of the total area. The first question to be answered is whether or not the hemodynamic performance of the mitral valve is affected by the configuration of the orifice (single versus double orifice). In the series published by Maisano et al, mean postoperative mitral valve area calculated by planimetric evaluation as well as by the modified Bernoulli method, showed a valve area of less than 2.5 cm2 in only 10% of the cases repaired using the edge-to-edge technique. This condition produced a minimal pressure gradient less than 4 mmHg across the valve and did not influence the postoperative course.

The second question is whether or not the design of the double orifice influences the hemodynamics (orifices of equal versus unequal areas). In a 3D computational model aimed at evaluating the hemodynamics of the double orifice repair, Maisano et al showed that for any given total orifice area, the velocities through the valve do not depend on the number of orifices and do not depend on the area ratio between the orifices ; accordingly, the pressure drops are not affected by the number of orifices or by the area ratio between the orifices. In the simulation of two orifices with different diameters, the symmetry of flow is lost even if the velocities are not appreciably different through the two orifices, regardless of the ratio between the areas of the two orifices. In the performed simulations, the lengths of the velocity jets decrease by increasing the total cross-area. The third question pertains to how Doppler-derived flow velocity analysis should be used to determine pressure gradients through the valve under the conditions of a double orifice flow pattern. Again, in the same experimental trial, Maisano et al showed that the maximum velocity was recorded laterally with respect to the center of the orifice. Simulations showed that the lateral flow can be considerably higher than the central one. When the maximum velocity at the center of the jets was considered for the pressure drop calculations, pressure gradients could be underestimated by up to 35%.

In conclusion, the edge-to-edge technique is reliable and simple. Effective orifice reduction does not seem to be a significant problem in patients with chronic mitral valve regurgitation with redundant preoperative mitral valve orifice areas. Relatively smaller orifices, such as in rheumatic valve disease, should be considered as a relative contraindication for this technique. Another matter of concern is that the remodeling of the subvalvular apparatus after the edge-to-edge technique could create a more turbulent flow, thereby decreasing the intraventricular pressure recovery and promoting the development of fibrosis in the area of leaflet approximation. These aspects provide for an intriguing field of investigation on the long-term impact of the Alfieri technique.® [7]

References