In North America, approximately 10,000 isolated primary mitral valve (MV) operations are performed annually, with increasing rates of MV repair. There are substantial advantages of MV repair compared with MV replacement in patients with degenerative MV disease, including lower operative mortality, improved left ventricular (LV) function, lower risk for stroke and infection, fewer complications related to anticoagulation therapy, and superior long-term survival. During the past few decades, repair techniques have evolved and improved, with different centers reporting excellent long-term results for degenerative MV disease. Current American College of Cardiology and American Heart Association guidelines for the management of patients with valvular heart disease recommend surgery for asymptomatic patients with chronic severe mitral regurgitation as long as there is high probability of MV repair with low operative mortality. The goal of achieving high rates of MV repair with good outcomes is dependent on surgical skills and techniques, linked to an understanding of the complexity of disease. The routine use of real-time three-dimensional (3D) transesophageal echocardiography has allowed highly detailed evaluation of the key anatomic information required for successful repair of degenerative MV disease, namely, the status of MV leaflets, chordae tendineae, and the MV annulus. There is a broad spectrum of degenerative disease causing MV prolapse, ranging from fibroelastic deficiency to advanced Barlow’s disease with marked leaflet thickening, hooding, elongated chordae, and marked annular dilation.
Although MV repair has been performed since the early days of cardiac surgery, Carpentier and colleagues are credited for having developed a rational functional classification of MV lesions and techniques of repair, such as anterior and posterior leaflet resection, chordal shortening and chordal transfer, and placement of a rigid annuloplasty ring. Important advances included the introduction of artificial polytetrafluoroethylene chordae in the mid-1980s that allowed replacement instead of shortening or transfer of diseased chordae and the development of the sliding annuloplasty technique when reduction of posterior leaflet height is required to avoid postoperative dynamic LV outflow tract obstruction due to systolic anterior motion of the MV leaflets. More recently, the introduction of minimally invasive and robotic repair techniques has shown promising short-term results.
It is well recognized that the MV annulus is not a fixed structure but changes its shape from a more circular and less steeply saddle-shaped configuration in diastole to a more elliptical and more steeply saddle-shaped configuration in systole, which results in a significant change of the MV annular area. Of course, these dynamics are affected in diseased MVs. MV annuloplasty becomes necessary whenever the MV annulus is dilated and the normal ratio of the anterior-posterior (AP) diameter to the anterolateral-posteromedial diameter is lost. In addition, more extensive MV prolapse may be associated with MV annular dysjunction. Annuloplasty rings have evolved over time as well: the surgeon can choose between rigid versus flexible, complete versus incomplete, and flat versus saddle-shaped rings. Rigid rings have an early negative influence on the LV systolic function, whereas a saddle-shaped annuloplasty ring improves leaflet coaptation geometry and reduces shear forces on the leaflets and subvalvular apparatus.
From an imaging perspective, the introduction of real-time 3D echocardiography and newly developed software that allows tracking of 3D structures over time has significantly improved assessment and pathophysiologic understanding of the MV annulus. This is an exciting advance, which will allow us to better assess the role of the MV annulus in the preservation of LV function and long-term outcomes.
In this issue of JASE , Ben Zekry et al. describe the effects of two different MV repair techniques on the dynamics of the MV annulus immediately after coming off cardiopulmonary bypass. Assessment was performed using real-time 3D transesophageal echocardiography in patients with degenerative MV disease and severe mitral regurgitation. Two surgical techniques were used: either (1) a more recently developed nonresectional dynamic MV repair (NVR) or (2) the more classic resectional MV repair (RVR). With the NVR approach, both MV leaflets and the MV annulus were left intact, polytetrafluoroethylene chordae were used for subvalvular support, and the MV annulus was reduced by the implantation of a complete flexible ring using a continuous suture technique. The RVR approach consisted of leaflet resection, the insertion of polytetrafluoroethylene chordae, and the implantation of a partial flexible ring or band attached with single stitches, when necessary. Each of these 2 surgical MV repair methods was performed at two different cardiovascular centers, with 15 patients included in the NVR group and 13 patients in the RVR group. Three-dimensional transesophageal echocardiographic images were acquired in the operating room, both before surgery and after coming off cardiopulmonary bypass, once the chest was closed. Analysis was performed offline, including the assessment of dynamic change in MV annular area in two and three dimensions, MV annular height and circumference, AP diameter, and anterolateral-posteromedial diameter as well as the mobility of the anterior and posterior leaflet. The patient populations were similar regarding their age and gender distribution, but not truly matched. Echocardiographic measurements showed that in the NVR group, dynamic changes of MV annular area, AP diameter, and posterior leaflet mobility were better preserved than in the RVR group. These results led the investigators to conclude that the NVR technique appears to be superior to RVR in the preservation of dynamic motion of the MV annulus and leaflet mobility. However, there are several concerns regarding the interpretation and significance of these results.
From a methodologic standpoint, it is a concern that the two different surgical techniques were performed at two different centers. The patient numbers were small, and the patients were not truly matched, which raises concerns regarding the accuracy of comparison. The degree of myxomatous degeneration, the number of segments of leaflet prolapse, the different types of rings and bands used and the techniques to secure them in the MV annulus, and the duration of CPB and aortic clamping varied widely. Aortic cross-clamp time was 137 min in the RVR group, which was more than double that in the NVR group. Other patient series providing results for MV repair after a resectional approach have reported substantially lower aortic cross-clamp times, with an average of 70 min, even for repair of bileaflet prolapse. It is not clear if these differences are meaningful to outcomes.
Understanding the dynamic behavior of the MV annulus may be important in degenerative MV disease and in other conditions as well. The use of real-time 3D echocardiography provides the ability to evaluate dynamic changes in MV annular motion and potentially to relate these changes to outcomes such as the preservation of LV function and survival. Ben Zekry et al. used this technique to show better preserved MV annular motion in the NVR group compared with the RVR group, specifically a greater change in the MV annular area and the AP diameter throughout the cardiac cycle along with better mobility of the posterior MV leaflet. The role of preserving MV annular motion after MV repair may be important but is not fully understood. It is possible that annular motion may play a role in patients with LV dysfunction, but it is unlikely that this would be the case when LV function is preserved, as it is in most patients undergoing MV repair. Another important consideration is the timing of assessment of MV annular motion. Ben Zekry et al. documented their findings in the immediate postoperative period and did not provide any data as to whether MV annular motion was better preserved in the intermediate and long-term period with the NVR versus the RVR approach. In our experience, fibrosis and pannus formation related to the annuloplasty material is not infrequent, and it usually takes up to 1 year for the MV annulus to be covered by scar tissue, which naturally would be expected to decrease MV annular motion. Therefore, reassessment of the MV annular motion 12 months after surgery would increase the validity of these very short-term findings.
Finally, the surgical techniques themselves require some consideration. The goal of traditional MV repair is to correct the anatomic abnormalities as completely as possible and limit the need for reoperation. Most experienced MV surgery centers choose an RVR approach on the basis of Carpentier’s principles, with a number of series reporting low reoperation rates during long-term follow-up. Lawrie et al. developed the interesting and novel nonresectional technique, which has some theoretical advantages, particularly the reduction of MV leaflet stress and improved MV annular motion. Recently, they reported their intermediate-term results in a patient cohort that underwent MV repair for MV prolapse from 1983 until 2008; after 1998, only the NVR technique was used, and this resulted in a 100% rate of reparability. Their overall perioperative mortality rate was 2.6%, which is higher than in other series in similar patient cohorts, who report an overall perioperative mortality of <1%. In addition, the reported predischarge echocardiographic data did not provide details regarding the presence of systolic anterior motion of the MV leaflets in the NVR group, which would be important to assess the success of the NVR technique in more complex patient groups. As well, long-term follow-up echocardiographic data were incomplete. In our experience, there is concern regarding the suitability of the NVR approach in patients with extensive myxomatous disease with Barlow-type MVs. In this complex patient cohort, correction of posterior MV annular displacement and a sliding annuloplasty is required to avoid dynamic LV outflow tract obstruction.
The study by Ben Zekry et al. will stimulate interest in the relative benefit of different surgical techniques available and whether improvement of MV annular motion is both sustained and clinically important. The concept of “less is more” applies to many things in everyday life and may ultimately be true for MV repair. Whether the NVR surgical technique and the choice of annuloplasty ring leads to long-term, meaningful improvement of MV annular motion and better long-term clinical outcomes needs to be proven. Considering the excellent long-term results reported for the RVR approach, it is important to prove that less is not simply less.