Thesis (M.D.)--University of Hong Kong, 1983.

Thesis (M.D.)--University of Hong Kong, 1983. / Also available in print.

published_or_final_version / Medicine / Master / Doctor of Medicine

Mitral valve (MV) prolapse (MVP) is the most common cause of surgical mitral regurgitation (MR) in developed countries. The normal mitral annulus is saddle in shape, connecting the left atrium (LA) and left ventricle (LV) into a functional entity, and is susceptible to distortion by LA and LV remodeling. Annular nonplanarity is important for alleviating mechanical stress on mitral leaflets and chordae tendinae. Recently, loss of annular saddle shape has been demonstrated as a novel mechanism in the pathogenesis of degenerative MR. Hitherto, the prevalence and features of annular flattening have not been well assessed in MVP patients, as well as potential factors related to annular flattening. / Current guidelines recommend MV repair as the preferred treatment for clinically significant MR. Annuloplasty are routinely used to restore the annular structure and function. Recent long-term studies showed that anterior leaflet or bileaflet prolpase was associated with suboptimal outcomes. However, the relation between mitral leaflets and annular geometry in MVP is not completely understood. / The application of two-dimensional (2D) echocardiography (ECHO) has been limited since mitral annulus has a nonplanar configuration. Three-dimensional (3D) ECHO was shown to be superior to 2D in defining the anatomy of MVP. In this thesis, MVP was identified as systolic displacement (≥2 mm) of any segment of mitral leaflets into the LA passing the mitral annular plane, as indicated in a long axis view (parasternal or apical three-chamber). Finally, 117 MVP patients consecutively referred to our echo laboratory for transesophageal echocardiography (TEE) were retrospectively studied. Twenty-nine patients referred for TEE for suboptimal transthoracic images, exclusion of endocarditis, or evaluation of cardiac source of embolic event and found to have no underlying structural cardiac disease or arrhythmia were included as the normal reference. Standard 2D transthoracic ECHO and 2D/3D TEE were performed in all the subjects. Custom software was used for quantification of 3D MV morphology and key geometric parameters, including mitral annulus, leaflets and chordae, were automatically measured. / The main findings were as follows: / 1. Annular saddle shape flattening (annular height to commisural width ratio <15%) was a common abnormality in MVP patients. More than 50% MVP patients had annular flattening. / 2. Atrial fibrillation (AF) and mitral annular disjunction (MAD) were found to be independent factors associated with annular flattening. MAD was associated with more severe myxomatous MV changes with excessive traction on papillary muscle. The potential roles of MAD in the development of myxomatous MV disease may be through excessive mobility of the mitral apparatus or disturbing 3D annular configuration with reduced annular height and loss of the saddle shape. / 3. Annular flattening was associated with advanced myxomatous MV changes and a higher prevalence of complex prolapse (anterior leaflet and/or bileaflet prolapse). Complex prolapse was associated with more severe annular flattening and dilation, leaflets elongation, increased billow volume and impaired mitral-aortic coupling. / In summary, this thesis provided new data of the 3D MV geometry in MVP patients with new insights into the mechanisms of disease progression and strategies to improve surgical outcomes. Using new techniques in 3D TEE, the thesis demonstrated that annular flattening is a common abnormality, associated with AF, MAD, and more advanced, complex lesions, with implication in the complexity and timing of MV repair. The results suggested that annuloplasty with saddle-shaped rings may be important to restore the structure and function of MV and to improve the durability of repair, particularly important for complex lesions. These data also implied that maintenance of sinus rhythm may help to prevent annular flattening and progression of MVP-related MR. Finally, MAD may be an echocardiographic marker of annular flattening and may require specific surgical correction. / 在發達國家，需要外科治療二尖瓣反流(MR)最常見的原因是二尖瓣脫垂（MVP）。正常二尖瓣瓣環是一個非平面的馬鞍型結構，連接左心房和左心室使之成為一個功能性整體，其結構和功能易受到心房和心室重構的影響。馬鞍型瓣環有助於降低瓣葉和腱索的機械性壓力。最新研究表明瓣環馬鞍型結構缺失是MVP患者出現退行性MR的發病機制。但沒有研究評估瓣環扁平在MVP患者中的患病率，相關特征性改變及引起瓣環扁平的因素。 / 目前，指南推薦二尖瓣修复術作為伴有嚴重MR的脫垂病人的首選治療方法。二尖瓣修复術中常規使用瓣環成形術有助於恢復瓣環的結構和功能。臨床研究顯示脱垂累及前葉或雙葉的手术预后不理想。目前尚不清楚瓣葉和瓣環幾何結構之間存在的相互關係。 / 由於瓣環的非平面結構，三維超聲評估二尖瓣脫垂的價值優於二維超聲。在本研究中，二尖瓣脫垂被定義為長軸水平（胸骨旁長軸或者心尖三腔切面）二尖瓣瓣葉的任何部分發生收縮期向左房面移位，并超過瓣環水平2毫米以上。最後，我們回顧性地研究了117名被轉診到我們心臟超聲實驗室進行經食道超聲檢查的MVP病人。本研究同時入組了29名无其他潛在結構性心臟病或心律不齊的正常對照。他們由於欠佳的經胸超聲圖質量，或者為了排除心內膜炎，或者為了評價血栓是否來自心臟接受了经食道超聲檢查。所有研究對象均接受了標準的二維經胸超聲及二維/三維經食道超聲檢查。研究採用專業軟件對受試者二尖瓣的三維形態進行定量分析。該軟件可自動測量二尖瓣的重要幾何學參數，包括瓣環，瓣葉和鍵索。 / 研究的主要發現包括： / 1.瓣環扁平（瓣環高度與連合線長度之比不超過15%）是一種常見的解剖學異常，超過50%MVP的患者罹患該種畸形。 / 2. 房顫和二尖瓣瓣環分離是引起瓣環扁平的獨立影響因素。瓣環分離與較嚴重的黏液樣改變以及過多的乳頭肌牽拉相關，其在黏液樣二尖瓣疾病中的作用可能是通過引起二尖瓣裝置的過度移動，或通過降低瓣環的高度導致馬鞍形結構缺失從而破壞二尖瓣裝置正常三維幾何學結構。 / 3. 瓣環扁平與嚴重的黏液樣改變有關，同時合併高比例的複雜脫垂（前葉和/或雙葉脫垂）。複雜脫垂與嚴重瓣環扁平和擴大，瓣葉冗長及隆起容積增加相關，同時破壞了二尖瓣-主動脈瓣耦合。 / 總之，本文對MVP疾病進展的機制提出了新的見解，并為手術治療提供有效的策略。本文採用三維經食道超聲領域中最新的成像和圖像分析技術并發現在MVP患者中瓣環扁平是一種常見解剖學發現，其發病與房顫，瓣環分離及嚴重和複雜病變有明確的相關性。這些發現有助於病變複雜程度分級和確定手術時間。採用馬鞍形瓣環成形術既可以修復二尖瓣的結構和功能又能提高修复的持久性。其重要性在複雜MVP患者中尤為明顯。盡早復律可預防瓣環馬鞍形結構缺失和防止反流的加重。最後瓣環分離可作為检测瓣環扁平的超聲學指標，可能需要特殊的外科矯正。 / Jin, Chunna. / Thesis Ph.D. Chinese University of Hong Kong 2015. / Includes bibliographical references (leaves 152-165). / Abstracts also in Chinese. / Title from PDF title page (viewed on 12, September, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

No description available.

Afhandling--Copenhagen. / Summary also in Danish. Bibliography: p. 253-258.

Afhandling--Copenhagen. / Summary also in Danish. Bibliography: p. 253-258.

No description available.

Thesis (M.S. in Bio. E.)--School of Biomedical Engineering, Georgia Institute of Technology, 2004. Directed by Ajit P. Yoganathan. / Includes bibliographical references (leaves 175-180).

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.