© Springer-Verlag London 2015
Khalil Fattouch, Patrizio Lancellotti and Gianni D. Angelini (eds.)Secondary Mitral Valve Regurgitation10.1007/978-1-4471-6488-3_1111. Papillary Muscle Relocation
(1)
Department of Surgery, University of Virginia School of Medicine, Charlottesville, VA, USA
Abstract
Ischemic mitral regurgitation results from the progressive interactions of left ventricular remodeling and dilatation following transmural infarction and mitral annular dilatation, primarily along the posterior annulus. As the left ventricle dilates and the sphericity index increases, the papillary muscles are displaced laterally toward the apex and the interpapillary distance increases, resulting in distortion of the subvalvular apparatus and leaflet tethering (Carpentier type IIIb mitral regurgitation). As this occurs, the mitral annulus becomes dilated (Carpentier type I mitral regurgitation).
Repair of ischemic mitral regurgitation with reduction annuloplasty has become the standard approach to restoring the normal anteroposterior dimension of the dilated mitral annulus, yet recurrence of mitral regurgitation following this procedure occurs in a significant number of patients. In one study comparing preoperative and postoperative echocardiograms of 585 patients undergoing isolated annuloplasty for ischemic mitral regurgitation, moderate to severe mitral regurgitation was present in 85 % of patients preoperatively. This was reduced to <10 % of patients in the immediate postoperative period but increased to affect 28 % of patients within 6 months of repair, after which time rates of recurrence stabilized. Use of an undersized ring did not correlate with postoperative regurgitation grade, suggesting other mechanisms of disease for surgical intervention (McGee et al., J Thorac Cardiovasc Surg 128:916–924, 2004). To further characterize these observations, a recent series compared mitral leaflet configurations before and after annuloplasty for ischemic mitral regurgitation. While tethering of both anterior and posterior leaflets contributes to preoperative disease, it is progressive tethering of the posterior leaflet following annuloplasty that results in early and late persistent/recurrent mitral regurgitation (Zhu et al., Circulation 112:I396–I401, 2005; Kuwahara et al., Circulation 114:I529–I534, 2006). This augmented tethering is likely due to an imbalance between a mobile posterior annulus, shifted anteriorly during repair, and a relatively fixed papillary muscle. Therefore, the emphasis has shifted to incorporating the subvalvular apparatus into the repair of ischemic mitral regurgitation.
Animal Studies
Many animal studies have offered insight into the mechanism of ischemic mitral regurgitation by focusing on treatment strategies aimed at papillary muscle relocation to alleviate leaflet tethering. Hung et al. examined an external device to realign the papillary muscles under the mitral annulus in an ovine model. A Dacron patch containing an inflatable balloon was secured over the region of an inferior infarct and the balloon was expanded under echocardiographic guidance to reposition the papillary muscles in a beating heart. Tethering distance was significantly decreased and moderate mitral regurgitation was immediately eliminated with either patch application alone or balloon inflation in all animals. There were no adverse effects on left ventricular contractility or coronary flow to viable myocardium [4]. Results were stable at 8 weeks despite increased left ventricular dilatation in a subset of animals, suggesting that the device supports the subvalvular apparatus and prevents further distortion [5].
In a related series of experiments, a polyvinyl-alcohol polymer was injected into the infarcted myocardium underlying the papillary muscles in an attempt to shift the subvalvular apparatus toward the mitral annulus and relieve leaflet restriction. Tethering distance and moderate mitral regurgitation was reduced without compromise in left ventricular systolic or diastolic function [6]. Similar results were seen in a chronic model of advanced ventricular remodeling [7].
The effects of isolated papillary muscle relocation on ischemic mitral regurgitation have been reported in an ovine model. Following induction of acute ischemic mitral regurgitation, repositioning the posterior papillary muscle toward the right fibrous trigone resulted in a decrease in mitral regurgitation, whereas repositioning toward the anterobasal left ventricular surface did not produce this effect. These results support the concept of restoring the posterolaterally displaced posterior papillary muscle to the normal subvalvular position in the treatment of ischemic mitral regurgitation [8].
Papillary muscle relocation as an adjunctive procedure to reduction annuloplasty was compared to reduction annuloplasty alone in a porcine model. In this experiment, two separate 2-0 Gore-Tex sutures were passed through each trigone, through each respective papillary muscle, and externalized at the base of each papillary muscle. These sutures were tightened on the epicardial surface and mitral leaflet configurations were assessed by 3-D MRI. The posterior papillary muscle was brought closer to the mitral annulus and lateral tethering was reduced in the group of animals undergoing adjunctive papillary muscle relocation [9].
In an in vitro model of ischemic mitral regurgitation, the mitral valve apparatus from ovine hearts was studied in a left heart simulator to determine the benefits of papillary muscle relocation as an adjunctive procedure to mitral annuloplasty. As the posteromedial or both papillary muscles were relocated toward the commissures or trigones, the tenting area and coaptation length were evaluated as markers of valve function on 3-D echocardiography. These variables were plotted against the distance of papillary muscle relocation in an effort to predict surgical outcomes. Overall, papillary muscle relocation improved leaflet tethering compared to mitral annuloplasty alone [10].
Clinical Results
Over the past decade, direct surgical intervention on the papillary muscles to restore normal annulopapillary geometry and alleviate leaflet restriction has been reported as an adjunct procedure to ring annuloplasty. In an initial study in this field, one group reported successful results in 18 patients who had sustained an inferior infarction and presented with moderate to moderately severe type IIIb mitral regurgitation. The technique consisted of placing a double-armed 3-0 prolene suture through the fibrous tip of the posterior papillary muscle and passing both needles through the mitral annulus just posterior to the right fibrous trigone. Mitral annuloplasty was then performed in all patients with 26–28 mm semi rigid rings. Follow-up transthoracic echocardiography at 2 months revealed mild mitral regurgitation in three patients and the remainder had none. The subvalvular apparatus was restored to a more physiologic configuration in these patients. Of note, this repair was recognized to be a quick additional procedure to ring annuloplasty, and could easily be performed with adequate visualization through the left atriotomy [11].
Many variations of papillary muscle relocation have since been reported. Menicanti et al. developed an intraventricular approach to alleviate ischemic mitral regurgitation after transmural anterior infarction. In this technique, a 2-0 prolene pursestring suture was sewn along the border of viable myocardium and around the base of the papillary muscles in order to restore left ventricular shape and volume, thereby resulting in papillary muscle imbrication and reduction of leaflet tethering. A concomitant reduction posterior suture annuloplasty was performed from the ventricular surface to alleviate annular dilatation. All 46 patients who underwent this procedure presented preoperatively with moderate to severe mitral regurgitation. The majority of patients (84 %) had no or mild mitral regurgitation on postoperative echocardiography. Late follow-up at 1 year on a subset of patients showed stable reapproximation of the papillary muscles together, reduction of the mitral annulus, and reduction of mitral regurgitation in the majority of these patients. NYHA functional class improved significantly, with the majority in class IV preoperatively and the majority in class I or II postoperatively [12].
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