Semi-rigid mitral annuloplasty rings improve myocardial stress adaptation compared to rigid rings: insights from in vitro and in vivo experimental evaluation.
OBJECTIVE
Investigate myocardial stress adaptation and remodelling capacity of a rigid and semi-rigid mitral annuloplasty ring.


METHODS
The annuloplasty rings were characterized in vitro in a mechanical setup with tensile and compressive forces from 0 to 3 N. The rings were tested with and without fixation of the ring to imitate the effect of annular implantation. In vivo measurements were performed with 21 porcine animals randomized into: A no ring group, a rigid ring group (Classic Annuloplasty Ring TM , Edwards Lifesciences) and a semi-rigid ring group (Physio I Annuloplasty Ring, Edwards Lifesciences). The rings were implanted together with a force transducer and sonomicrometry was used for geometry measurements.


RESULTS
The flexibility range of the semi-rigid ring was 7.6 and 2.4 mm in the septal-lateral and commissural direction, respectively. With fixation the flexibility was reduced to 1.0 and 0.6 mm, similar to the rigid ring without fixation. In vivo measurements indicated that the rigid and semi-rigid rings equally restrict the annular movement. Septal-lateral flexibility of the semi-rigid ring was not observed. Both rings induced force absorption in the ring and sutures due to the annular fixation. The absorbed forces were significantly lower for the semi-rigid ring in the posterior segment and septal-lateral direction.


CONCLUSIONS
This study demonstrates the importance of correct fixation when characterizing annuloplasty rings. The annular movement of the semi-rigid ring was similar to the rigid ring when implanted at the mitral annulus as confirmed in vitro . Despite this the semi-rigid ring demonstrated a favourable stress adaptation which could potentially decrease the risk of ring dehiscence.
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Søren Nielsen
SN
Skov
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Diana Mathilde
DM
Røpcke
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Marcell Juan
MJ
Tjørnild
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Christine
C
Ilkjær
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Jonas
J
Rasmussen
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Hans
H
Nygaard
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Biomedical Engineering, University of Arkansas, Fayetteville, AR, USA.
Morten Olgaard
MO
Jensen
Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Aarhus, Denmark.|Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
Sten Lyager
SL
Nielsen
D000818:Animals; D001696:Biomechanical Phenomena; D006321:Heart / Q000502:physiology; D006350:Heart Valve Prosthesis; D008943:Mitral Valve / Q000502:physiology* / Q000601:surgery*; D058386:Mitral Valve Annuloplasty / Q000295:instrumentation*; D018583:Pliability; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013552:Swine
Annuloplasty ring dehiscence; Mitral annular stress adaptation ; Mitral valve ; Mitral valve annuloplasty ; Semi-rigid annuloplasty ring 