A hydrophilic protein-rich part, called the rough zone, starts ~1 cm from the distal leaflet tips and helps to ensure a perfect seal between the leaflets, termed the co-aptation zone. The normal atrial surface of the leaflets is smooth. The normal ratio of mitral annulus to mitral leaflet area is 1.5–2.0, and is vital to prevent significant MR in normal, and even dilated left ventricles ( 12). Redundant leaflet tissue is very important for tight leaflet co-aptation and sealing. Leaflet tissue is attached to the MA, and the normal tissue length is between 0.5 and 1.0 cm ( 12). The mitral valve has anterior and posterior leaflets and variable commissural scallops to occlude medial and lateral gaps ( Figure 2). Despite this high burden, significant mitral valve disease is uncommon in patients younger than 65 years. The mitral valve leaflets fully open and close up to 3,000,000,000 times throughout a lifetime ( 11). Several recent investigations using advanced imaging modalities reported an average mitral annular area of ~10 cm 2 in healthy subjects ( 8– 10), much larger than the widely believed “normal” mitral annular orifice area of 4–6 cm 2.
The MA is innervated and supplies blood vessels to the leaflets ( 6, 7). Some have postulated it is related to tethering of the anterior annulus to the aortic root combined with apical translation of the “loose” posterior annulus resulting in folding across the inter-commissural axis.
The mechanism for this early saddle-shape accentuation is disputed.
#COMPLETE ANATOMY AND PHYSIOLOGY OF THE HEART MOVIE#
This mechanism may be important in preventing early systolic mitral regurgitation ( Supplementary Movie 1). In other words, when early-systolic ventricular pressure is still relatively low, leaflet approximation by annular contraction and saddle shape accentuation results occurs even before LV pressure rises, locking the leaflets together. This contraction leads to very early-systolic annular area contraction, accentuation of saddle shape, and approximation of anterior and posterior leaflets. However, in early-systole, during the iso-volumic contraction period, antero-posterior contraction occurs, resulting in folding across the fixed inter-commissural diameter. They have showed that variation of annular size throughout diastole is minimal. Recent studies, using 3-D echocardiography ( 1, 4, 5) have assessed the normal mitral annulus changes over the cardiac cycle. The angle between the MA to the aortic annulus changes during the cardiac cycle through the mitral aortic fibrous continuity ( 3). In the second part we will focus on the pathologic anatomic and physiologic derangements associated with different types of MR. In this review we will focus first on normal anatomy and physiology of the different parts of the mitral valve (MA, leaflets, chordae tendineae, and PM). Understanding the anatomy and physiology of all the component of the mitral valve is important for the diagnosis, and for optimal planning of repair procedures.
Abnormal function of any one of the components, or their interplay can result in mitral regurgitation (MR). Normal valve function is dependent on the integrity and normal interplay of these components. The main components of the mitral apparatus are the mitral annulus (MA), the mitral leaflets, the chordae tendineae, and the papillary muscles (PM) ( Figure 1). The normal mitral valve is a dynamic structure that permits blood to flow from the left atrial (LA) to left ventricle (LV) during diastole and sealing of the LA from the LV during systole.
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