Surgical management of ischemic mitral regurgitation: an in-vitro investigation

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Rabbah, Jean Pierre
Yoganathan, Ajit P.
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Owing to its complex structure and dynamic loading, surgical repair of the heart’s mitral valve poses a significant clinical burden. Specifically, repair of ischemic mitral regurgitation, which is caused by the geometric disruption of the mitral apparatus in the setting of ventricular dysfunction, results in poor long-term patient survival. Clinical data have shown that the preferred surgical treatment, restrictive mitral annuloplasty, may result in 15-30% early (< 6 months) recurrence of mitral regurgitation; this may exceed 70% after five years. Studies have suggested that isolated annuloplasty may not be a comprehensive repair suitable for all patients because ischemic pathology is multi-factorial and results in variable ventricular and valvular geometric distortions. Therefore, in this thesis, a new surgical planning paradigm was developed through three specific aims. In specific aim 1, in collaboration with Philips Healthcare, a novel tool to more accurately and quantitatively assess mitral valve insufficiency was developed and rigorously validated using the Georgia Tech Left Heart Simulator. This tool was found to be more efficacious and robust than the current clinical standard. Ultimately, this improved diagnostics may better inform surgical indication, specifically, to identify patients that may not benefit from simple ring annuloplasty. In specific aim 2, targeted adjunctive surgical repair for such patients were investigated. Anterior leaflet augmentation and basal papillary muscle relocation were observed to restore mitral valve function while reducing the leaflet-subvalvular tethering associated with ischemic left ventricular remodeling. These efficacious repairs were found to be robust to variability in surgical implementation, which may encourage more widespread clinical adaptation. Finally, in specific aim 3, an integrative experimental framework was developed to promote pre-operative patient specific evaluation of mitral valve surgical repair using novel computational methods. The experimental framework combined high-resolution state of the art imaging with clinical imaging to provide the most realistic anatomical reconstructions possible. For the first time, ventricular flow fields through and proximal to a native mitral valve were acquired using stereoscopic particle image velocimetry. These data were combined with measurements of leaflet dynamics and subvalvular forces to create a comprehensive database for the rigorous validation of mitral valve finite element and fluid-structure interaction models. Collectively, these studies comprise a surgical planning paradigm that may better inform repair of mitral valve insufficiency.
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