The Mitral Valve Complex: Divine Perfection

Abstract

T he characteristic term mitral valve for the left atrioventricular valve was first suggested by Andreas Vesalius because of its resemblance to a bishop's miter. The mitral valve has 2 leaflets with different shapes and circumferential lengths, and these leaflets act together to prevent back flow to the left atrium during the ventricular systole. The anterior leaflet, which is in fibrous continuity with the aortic valve, occupies one third of the annular circumference with a rounded free edge. The posterior leaflet is long, narrow, and composed of 3 distinct scallops-medial, middle, and lateral-that line the remainder of the circumference of the annulus.1 The mitral valve coapts effectively when all the related components surrounding the leaflet act properly. The mitral valve complex, which is composed by (1) annulus, (2) leaflets, (3) chordae tendineae, (4) papillary muscles, and (5) left ventricular wall, is miraculously balanced both geometrically and functionally. See Article by Ben Zekry et alThe annular and subvalvular geometry and mechanical relationship among the mitral valve apparatus were originally investigated in animal models with the use of tracking materials, such as crystals or radiopaque markers.2-4 These experimental studies contributed to the pathophysiological assessment of the mitral valve complex under various cardiac conditions, such as ischemic mitral regurgitation (MR) or pre/ postsubvalvular repair surgery. In the 1990s, development of 3-dimensional (3D) echocardiography gave us new insights into the complexities of the mitral valve, including its unique saddle-shaped mitral annulus and elegantly curved leaflet scallops, information which was previously unavailable from 2D echocardiography.5 Although the 3D acquisition was time consuming and the image quality was limited in the first-generation 3D echocardiography, many clinically important analyses were done both in clinical and experimental studies. Extracted 3D images made it possible to evaluate the flexibility of the annuloplasty ring in humans, which had a great effect on surgical practice.6 3D echocardiography also gave new insights into the assessment of secondary (functional/ischemic) MR. 3D measurements of the valve apparatus contributed to proving the leaflet-tethering phenomenon, which is now believed to be a principal mechanism of secondary MR, mainly from experimental animal studies. 7,8 In the beginning of the 21st century, transthoracic real-time 3D echocardiography became commercially available, followed by transesophageal realtime 3D echocardiography. Real-time 3D echocardiography allows one to noninvasively obtain whole-heart images at the bedside, and some dedicated software has made it possible to reconstruct realistic images of the mitral valve apparatus and quantify the degree of geometric changes of the mitral valve complex. Our group has reported the 3D assessment of the mitral valve remodeling in ischemic/functional MR by using transthoracic and transesophageal echocardiography.9-12 The saddle-shaped mitral ann...