Page 65 - Read Online

Page 2 of 12 Cepas-Guillen et al. Vessel Plus 2021;5:26 https://dx.doi.org/10.20517/2574-1209.2020.79

[4]
the aortic valve . Nonetheless, over the last years, development of new techniques and devices, improved
patient selection, and dedicated imaging assessment and guidance tools seem to offer novel alternative for
percutaneous MV treatment. The present review aims to provide an update of the available percutaneous
techniques for patients with severe MR.

MITRAL VALVE ANATOMY
The MV is a complex and dynamic three-dimensional structure that allows blood inflow into the left
ventricle (LV) during diastole and seals the left atrium (LA) from the LV during systole. The MV is
composed by several elements: mitral annulus, mitral leaflets, and subvalvular apparatus with tendinous
chords and papillary muscles [Figure 1]. For correct valve function, the integrity of these components
[5]
along with LV and LA is essential: an imbalance in any of these components might lead to an incompetent,
stenotic, or both valve dysfunctions . A detailed understanding of the MV is important for appropriate
[6]
patient selection and percutaneous correction technique.

Mitral valve annulus
The MV annulus is a dynamic, D-shaped orifice that connects the LA, LV, and mitral leaflets. The angle
between the MV annulus and aortic annulus is dynamically modified over the cardiac cycle due to the
displacement of the aortic-mitral curtain. In addition, a fibrous continuity attaches the anterior leaflet of the
MV with the aortic valve . Whereas the anterior mitral annulus is tightly attached to the surrounding
[8]
structures, the posterior mitral annulus is not as anchored. This is why annular dilatation and calcification
[9]
appear more commonly in the posterior mitral annulus, leading to inadequate leaflet coaptation and MR .
Mitral valve leaflets
The MV has anterior (aortic) and posterior (mural) leaflets which are contiguous through the medial and
lateral commissures. In general, the anterior leaflet is larger, longer, and thicker than the posterior leaflet,
occupying one third of the annulus circumference. It is arbitrarily divided into three scallops: lateral (A1),
central (A2), and medial (A3). As opposed to the anterior leaflet, the posterior leaflet is crescentic with a
long circumferential base and relatively short radial length, occupying two third of the annulus
circumference. The posterior leaflet is divided into lateral (P1), central (P2), and medial scallops (P3) by the
[9]
presence of two indentations in its free border . The leaflets coapt over a height of 8 mm on average in
systole. This “coaptation reserve” prevents the development of MR in cases of annular dilatation.

Tendinous chords
The tendinous chords originate from the papillary muscle tips and are implanted into the leaflets. Although
highly variable, there are two main types of tendinous chords: primary (marginal) and secondary (basal)
chords. Some differences are observed among them : primary chords are thinner than basal chords, and
[5]
they are inserted into the leaflet tips, limiting extensibility to prevent leaflet prolapse, while basal chords
[10]
have more extensibility and are only attached in the ventricle surface of the posterior leaflet .

Papillary muscles
The anterolateral and posteromedial papillary muscles originate from LV and connect through tendinous
chords to the corresponding anterior, posterior, and commissural leaflet portions. The anterolateral
papillary muscles have a single head and dual blood supply from the left circumflex and left anterior
descending artery. The posteromedial papillary muscles have two heads and are supplied by either the right
or circumflex coronary artery based on coronary dominance. The papillary muscles, among the tendinous
chords, prevent leaflets prolapse and maintain the leaflets coaptation during systole. Any alterations in
ventricle geometry involve MV coaptation due to papillary muscles displacement. This might occur in cases
of LV remodeling due to myocardial ischemia, translating into MV tethering and MR appearance .
[11]