Ann Thorac Surg 2005;80:197
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Tomasz A. Timek, MD
Department of Cardiothoracic Surgery, Stanford University, CVRB Building 2nd Floor, 300 Pasteur Dr Stanford, CA 94305
(Email: kotek1{at}stanford.edu).
The mitral valve is a finely orchestrated complex structure working in synchronicity to achieve timely and efficient valve function. Although most clinical attention has been focused on anatomy and dynamic physiology of the mitral annulus, scientists and surgeons alike have considered mitral leaflets and chordae to be essentially inert and passive structures at the mercy of the hemodynamic ebb and flow of myocardial contraction. However, recent human and animal studies are steadily eroding the dogma. Valvular tissue has been shown to have rich afferent and efferent innervation and intrinsic contractile properties. The leaflets have a gradient of collagen fiber orientation for optimal stress distribution, and differential load bearing is reflected in the size and ultrastructural properties of the chordae tendinea. Thus, the valvular apparatus appears neither homogenous nor passive.
The current experimental study presented by Ritchie and colleagues provides valuable insight into porcine mitral valve chordal microstructure and leaflet blood supply. The investigators demonstrate differential ultrastructure, collagen content, and collagen turnover based on chordal type, and they provide evidence for a novel pathway of blood and nutrient delivery to leaflet tissue through the ascending chordal vessels. The current findings corroborate the mounting evidence supporting active involvement of leaflets and chordae in maintaining and regulating normal valve function. Similar work of other investigators has already led to the recognition that normal appearing leaflets and chordae, as those found in functional mitral regurgitation, have significant ultrastructural abnormalities. Although the present analysis does not permit direct functional correlation of these findings, one is moved to ponder the clinical implications of the data. As mitral valve repair is becoming the gold standard for correcting many valvular lesions, procedures such as chordal replacement, transposition, and even severance have been incorporated into the modern surgical armamentarium, but such interventions may be deleterious if chordal form is dissociated from native function or if nutrient supply to valvular tissue is compromised. Leaflet altering procedures may be equally unpredictable if variations in ultrastructure and histology are ignored. Surgeons are rarely challenged to focus on such microscopic circuitry; yet understanding these innate intricacies of valvular tissue will yield more rational approaches to local mitral valve repair and potentially improve clinical outcomes. It is time to zoom in on the valve.
Related Article
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Structural Characterization of the Chordae Tendineae in Native Porcine Mitral Valves
- Jennifer Ritchie, James N. Warnock, and Ajit P. Yoganathan
Ann. Thorac. Surg. 2005 80: 189-197.
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