Editorial Comment: Mitral repair for functional mitral regurgitation in idiopathic dilated cardiomyopathy: a good operation done well may help

Abstract

In this issue, De Bonis et al. [1] described a very interesting retrospective series of 54 patients with idiopathic dilated cardiomyopathy who underwent mitral valve repair for severe functional mitral regurgitation. No patients had coronary artery disease. These patients, very typically, had severe mitral regurgitation, class III–IV New York Heart Association failure with large ventricles, poor ejection fractions, and many had atrial fibrillation and tricuspid regurgitation. In this series, as has been shown by others, the patients underwent correction of their mitral regurgitation with low in-hospital mortality (5%). The actuarial survival at 6.5 years was 70%. The survival was further improved if the patients had either atrial fibrillation ablation or cardiac resynchronization therapy. In follow-up, patients showed improvement in their left ventricular geometry, ejection fraction and in NYHA class. Most importantly, in this series, the freedom from recurrence of significant mitral regurgitation was 90% at 6.5 years. Functional mitral regurgitation is a complication of idiopathic dilated cardiomyopathy, occurring secondary to left ventricle geometrical distortion from stenting, inferobasilar migration, apical displacement, annular dilation and posterior leaflet restriction, with altered ventricular shape and/or regional LV wall dysfunction. Mitral regurgitation (MR) leads to a vicious cycle of LV volume overload, geometric distortion and progressive MR. MR complicating congestive heart failure (CHF) predicts poor survival [2]. Mitral reconstruction surgery to treat MR in dilated cardiomyopathy has been undertaken with an acceptably low operative mortality [3, 4]. However, MR surgery for these patients remains controversial, as substantial residual or recurrent MR has been noted, and may mitigate any benefits. In fact, some series show an early (6 months) recurrence rate of significant MR of up to 50%, which certainly negatively influences or obscures potential survival advantage [5, 6]. When reviewing literature series of both surgical and percutaneous outcome studies on patients with MR in dilated idiopathic cardiomyopathy, one should be critically aware of the negative impact, mechanism and rates of recurrent MR. At present, many of the mechanisms of recurrent functional MR have been elucidated and include annular level and subvalvular components. Predictors of recurrent MR have included LV size >65 mm, a coaptation depth of >1 cm below the annular plane and angulation of the mitral valve apparatus, all of which indicate a degree of LV distortion [6]. We have also learned that the intertrigonal distance is not stable, with dilatation occurring along both the insertion of the posterior leaflet, but also in the anterior portion. This intertrigonal portion dilates and, although at one time, was considered to be a stable ‘measurable’ standard by which to size annuloplasty rings, we now know from a landmark paper of Hueb et al. [7] that this is not the case. Therefore, our previous method of sizing was incorrect and ‘undersizing’ rings has become the standard for these functional MR patients. This may partly explain the operation ‘failing’ and recurrence of mitral regurgitation in functional MR patients when using too large ‘standard-sized’ rings or when using a partial or flexible rings. Perhaps, the most important mechanistic predictor of recurrent mitral regurgitation is an increased anterior–posterior or septal– lateral mitral annular diameter. This CHF-related change has been shown not only in animal models, but also in humans. Three-dimensional magnetic resonance imaging and echo studies showed that the mitral annulus flattens and significantly increases its anterior-posterior (AP) diameter. Kongsaerepong et al. [8] found that the strongest predictor of a recurrent MR, following mitral repair, was a residual large AP diameter, i.e. a ‘too large’ ring size. Finally, Spoor et al. [9] demonstrated that the use of flexible rings (which flex and allow the largest AP diameter) as opposed to a rigid complete ring was associated with a five times higher recurrent mitral regurgitation rate. At present, numerous rigid, complete rings with stable AP dimension reduction are available [10]. In this present series, all patients were uniformly treated with an undersized rigid complete ring. The authors noted an extremely low long-term rate of recurrent MR, with excellent LV remodelling and survival. The use of a rigid complete ring has been adopted for these functional MR patients by a majority of surgeons and is becoming our best practice standard. Of course, many factors in these difficult patients determine the long-term outcome including patient comorbidities, some of which (atrial fibrillation, tricuspid regurgitation, cardiac resynchronization therapy) have been shown by these authors to be beneficial when corrected. In dealing with functional MR in idiopathic cardiomyopathy, it has been noted that a good operation when done poorly will not help; however, the manuscript by De Bonis et al. reveals that a good operation done well will help these functional MR patients.