Biomechanics of Annular and Sub-annular Repairs for Functional Mitral Regurgitation
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Xu, Dongyang
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Abstract
Functional mitral regurgitation is commonly diagnosed in heart failure patients. It has been shown to worsen prognosis, double mortality and increase hospitalization. One of the current standards to correct functional mitral regurgitation is known as undersizing mitral annuloplasty ring, in which a metallic ring-like structure is surgically sutured onto the mitral annulus to reduce its size so that the leaflets are brought back into coaptation to enable regurgitation correction. However, numerous studies have pointed out the clinically sub-optimal outcomes of the ring, illustrated by moderate to severe regurgitation reoccurrence and limited left ventricular functional recovery. Therefore, there is a need to understand the mechanistic basis of such unsatisfactory outcomes and to investigate more optimal surgical repairs. Our preliminary work has shown that annuloplasty ring, by drawing the posterior annulus forward, further restricts the motion of the posterior leaflet and makes anterior leaflet hyperextended, creating a “unicuspid” valve. Also, the ring deforms the LV basal myocardium into a curved structure that might impair its normal function. These observations have led me to hypothesize that ring unphysiologically alters the shape and biomechanics of both mitral valve and LV, which can potentially induce regurgitation recurrence and restrict ventricular reverse remodeling. In addition, I believe the optimal repair for functional mitral regurgitation should aim at relieving such unphysiological mechanics, which is expected to improve repair outcomes. In this thesis, I first showed that gradually downsizing the mitral annulus with the ring worsens mitral valve diastolic hemodynamics, fails to relieve valve tethering and mechanics. Second, I modified the traditional annuloplasty ring by performing segmental downsizing, which was shown to improve diastolic hemodynamics and slightly improve valvular tethering. Last, I investigated sub-annular repair in the form of papillary muscle approximation, which was shown to significantly improve mitral valve motion, tension and forces and better preserve ventricular function compared to annuloplasty ring. Together, data from this thesis point out the underlying mechanics for sub-optimal outcomes of traditional annuloplasty rings and suggest the usage of sub-annular technique as a more biomechanically favorable repair for functional mitral regurgitation.
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2022-04-29
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Dissertation