Remodelling Forces of a Rigid Mitral Annuloplasty Ring - A Potential Risk Factor for Ring Dehiscence in Mitral Valve Repair?
Søren Nielsen Skov1,2,3, Diana Mathilde Røpcke1,2, Christine Ilkjær1,2, Jonas Rasmussen1,2, Marcell Juan Tjørnild1,2, Hans Nygaard1,2, Morten Olgaard Jensen1,4 and Sten Lyager Nielsen1,2
1 Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark
2 Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark
3 Department of Engineering, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark 4 Department of Biomedical Engineering, University of Arkansas, Fayetteville, AR, USA
Mitral annulus reconstruction with a remodelling annuloplasty ring is an essential part of the surgical treatment for mitral regurgitation. Force accumulation at the attachment of the annuloplasty rings may be a potential risk factor for ring dehiscence and repair failure.
The aim of this study was to conduct an in-vivo assessment of the remodelling forces of a rigid mitral annuloplasty ring compared to the native mitral valve.
Materials and Methods
Measurements were performed in-vivo in an 80 kg porcine model. Seven animals received a rigid normal-sized annuloplasty ring (CE Classic Ring, size 32) and 7 animals were used as controls in a no ring group. Mitral annular forces were obtained with a novel annular force transducer (Figure 1) and geometry was measured with a sonomicrometry technique based on 8 implanted crystals dividing the annulus circumference into four segments (Figure 2).
Force measurements were performed with the transducer attached to the annuloplasty ring (Figure 3) or directly onto the mitral annulus for the no ring group. For geometry measurements the transducer was removed on a beating heart to avoid restriction of the mitral annulus.
The difference in force measurements between the two groups reflects the forces that are accumulated within the annuloplasty ring and the sutures attaching the ring to the mitral annulus.
Figure 1: X-shaped mitral annular force transducer illustrated with force directions and strain gauge locations. ANT, Anterior; POST, Posterior; ACOM, Anterior commissure; PCOM, Posterior commissure; SL, Septal-lateral; CC, Commissure-commissure; SG, Strain gauge.
Figure 2: The mitral annulus was divided into four segments based on the 8 sonomicrometry crystals, indicated with red dots.
Figure 3: Transducer a>ached to annuloplasty ring prior to insertion.
Results and Discussion
Rigid ring implantation significantly reduced mitral annular motion in the posterior segment, both commissural segments and the septal-lateral direction compared to the no ring group (Figure 4, upper left). This resulted in a significant reduction of deformational forces (>50%) in the mitral annulus anterior commissural segment and the commissure-commissure direction, which reflected the remodelling forces accumulated in the rigid ring (Figure 4, upper right). The accumulated forces in the rigid ring (difference between groups) indicated significant forces especially in the septal-lateral and commissure-commissure direction (Figure 4, below).
Figure 4: Cyclic differences in both geometry and forces (above). The accumulated forces in the rigid ring are shown below for each strain gauge position. ANT, Anterior; POST, Posterior; ACOM, Anterior commissure; PCOM, Posterior commissure; SL, Septal-lateral; CC, Commissure-commissure.
The rigid annuloplasty ring significantly restricted cyclic annular dynamics and reduced force transmission from the mitral annulus compared to the native mitral valve. We anticipate that this difference in force transmission corresponded to the remodelling forces accumulated in each annular segment. A significant force accumulation in the ring itself and suture attachment might potentially lead to ring dehiscence and repair failure.
This project was funded by the Danish Heart Foundation Grant #14-R97-A5166-22830, Karen Elise Jensens Fond, Arvid Nilssons Fond, Aase og Ejnar Danielsens Fond, Knud og Edith Eriksens Mindefond, Raimond og Dagmar Ringgård-Bohns Fond, Snedkermester Sophus Jacobsen & Hustru Astrid Jacobsens Fond, Helga og Peter Kornings Fond and Oticon Fonden.