Comparative Anatomy of Mitral and Tricuspid Valve: What Can the Interventionlist Learn From the Surgeon

Figures

• 

  Figure 1. Comparison of the atrial septal surfaces. (A). The septal surface of the left atrium is characterized by the flap valve of the fossa ovalis (septum primum), in contrast to the limbus of the fossa ovalis (*) present on the right atrioseptal surface (B). The source of light indicates the fossa ovalis, the blue band depicts the position of the aortic non-coronary sinus. LA, left atrium; MV, mitral valve; SP. septum primum; IVC, inferior vena cava; RA, right atrium; RAA, right atrial appendage.

• 

  Figure 2. The annulus fibrosus of the mitral is a discontinuous band of connective tissue that exists only in some parts of the attachment of the posterior leaflet, between the two fibrous trigones (red asterisks). The annulus does not exist at the attachment of the anterior leaflet, because the leaflet tissue is continuous with the aorto-mitral curtain that extends from the aortic valve annulus to the base of the anterior leaflet. During the diastole, the shape is grossy circular; during systole it has a saddle shape, with antero-septal diameter significantly smaller than the intercommissural diameter. The anterior leaflet is primarily related to the left ventricular outflow tract via the aorto-mitral curtain, whereas the posterior one is related to the muscular parietal base of the left ventricle. The systolic reduction of the mitral orifice is around 25%, due to the contraction of the base of the heart and the displacement of the aorto-mitral curtain toward the center of the orifice. P1-P3, posterior scallops of the mitral leaflet; A1-A3, anterior scallops; MV, mitral valve; Courtesy of Dr. M. Reisman, University of Washington.

• 

  Figure 3. The anterior leaflet of the TV is larger than the posterior, which is larger than the septal leaflet. The anterior leaflet is primarily attached to the right ventricular outflow tract, the posterior to the muscular wall of the right ventricle and the septal one to the septum. The anterior has a semicircular shape and likewise the MV, it is divided into an atrial zone, regular, and thin, and into a distal zone, the zone of coaptation, slightly irregular and thicker than the proximal one. In comparison to the MV, few chordae are attached to the ventricular side of the leaflet. The posterior leaflet, slightly smaller than the anterior is divided in the same proximal and coaptation zones. The septal leaflet is the smaller and less mobile, and roughly semicircular and likewise the other two leaflets, it has a proximal and a coapting zone. The commissures of the TV are three and separate the three leaflets (red asterisk). They are small semilunar leaflets, attaching on the annulus and with a free edge attaching characteristics fan-like chordae. There is one variable to take into account: in comparison to the left, the septal attachment of the TV is at a more apical level than the…

• 

  Figure 4. Cross-sectional view of the three heart valves seen from above with atria removed. Advanced editing of a computed tomography image performed with 3mensio (Pie Medical Imaging, Netherlands) software. The proximity of the atrioventricular valves (different area can be appreciated) to the coronary arteries that are located in the atrioventricular groove (the circumflex for the mitral and the right coronary artery for the tricuspid) represents a similar aspect to be taken into account. Cx, circumflex artery; AVN, atrioventricular node; RCA, right coronary artery.

• 

  Figure 5. The leaflets of the MV are clearly divided into two regions, the atrial zone which is at the base of the leaflets (green clear zone), thin and translucent, and the zone of coaptation, which is the distal rough and irregular zone (red rough zone), where numerous thick chordae origin and attach the leaflets to the PMs. Three types of chordae tendineae can be described: tertiary chordae which origin normally directly from the LV and are attached to the base of the posterior leaflets and commissure. The secondary chordae (Strut) extend directly from the PM and are attached to the body of the leaflets, ventricular side. The primary chordae (marginal), the most represented and robust, are attached to the free margin of the leaflets and the space between them is never more than 3 mm. The attachment to the free margin is normally bifurcated or trifurcated. When they are considered upon their position, it is possible to recognize one thick and resistant ≪ main chorda ≫ attached to the ventricular surface of the leaflet which forms with the opposite main chord a kind of arcade, supporting the center part of the leaflet. The commissural chordae, attached to the commissural tissue, are…

• 

  Figure 6. Multimodality imaging of the TV. (A) Deep transgastric 2D TEE view, displaying the TV in short axis from the ventricular side. (B) Same en face view derived from MSCT angiography. (C) Short-axis atrial view of the TV on 3D TEE and during surgery (D). Red asterisks are the commissures. AL, anterior leaflet; LV, left ventricle; PL, posterior leaflet; RV, right ventricle; SL, septal leaflet. This image has been adapted from Taramasso et al. (1).

• 

  Figure 7. Comparison of mitral and tricuspid PMs. (A,B) Each group of papillary muscles comprises either a single bulky papillary with multiple heads or otherwise several thinner papillary muscles from which arise the numerous chordae attaching to the leaflets. They are implanted on the muscular wall of the left ventricle at a junction situated ~1/3 from the apex and 2/3 from the annulus. The position is varying little: the anterolateral PM is implanted at the junction between the septum and the posterior wall of the ventricle. The postero-medial PM is inserted on the lateral wall of the ventricle. The length of the PMs is variable, ranging from 2 to 5 cm. Importantly, no PMs attach to the left side of the ventricular septum.

• 

  Figure 8. The TV has a more complex chordal structure in comparison to MV. The chordae can be attached directly to the RV wall and septum, differently from the LV. On average, a number of 25 chordae inserts into the TV. The chordal system is hierarchical similar to the left one, dividing the types of chordae in basal, intermediary or secondary chordae and the marginal chordae, attaching to the free edges. The attachment of the marginal or primary chordae is usually single on the right, without bifurcating or trifurcating close to the edge and originating from various levels of the papillary muscles. Even if thinner, the chordae of the TV commissures are trifurcated with a characteristic fan-like disposition. CT, Chordae tendineae; PM, papillary muscle; MV, mitral valve; TV, tricuspid valve. LMCA, left main coronary artery (light blue circle). Courtesy of Dr. M. Reisman, University of Washington.

• 

  Figure 9. The septal surface of the LV may be considered to have a sinus portion, most of which is trabeculated, and a smooth outlet (LVOT) portion (A). The part of the sinus portion of the septum immediately beneath the mitral valve may be termed the inlet septum, and the rest of the sinus portion, the trabecular septum. The LVOT lies in front and to the right of the anterior mitral leaflet, corresponding to the inlet portion on the right ventricular side of the septum, and includes the atrioventricular septum. On the right side, the septal leaflet is the only one attached to the septum, but it leaves the RVOT free (B). The lowermost of the small septal muscles attaches posterior to the trabecula septomarginalis and the uppermost, called the medial or conal PM (muscle of Lancisi), to the posterior limb of the septal band. The septal PM is almost not affected by tethering in case of RV dilatation. LVOT, left ventricular outflow tract; AV, aortic valve; AML, anterior mitral leaflet; MPMs, mitral papillary muscles; RVOT, right ventricular outflow tract; TPMs, tricuspid papillary muscles. This image has been adapted from Taramasso et al. (1).

• 

  Figure 10. The right outlet portion of the ventricular septum is smooth and has three components. The largest is the infundibular septum, which separates the pulmonary valve (with arrow) from the aortic and TV. A second part of the outlet portion of the septum is the anterior extension of the trabecular septomarginalis (septal band). A third small, very anterior portion is a narrow extension superior to the trabecular septum. The axes of the right and left ventricular outflow tracts differ significantly. That of the RV is almost vertically oriented, whereas that of the left ventricle angles sharply to the right, a characteristic criss-cross feature (white and black empty arrows), visible under fluoroscopy in the left anterior oblique projection and in the parasternal long axis view by two-dimensional echocardiography. RA, right atrium; Ao, Aorta; RV, right ventricle; PT, pulmonary trunk; LV, left ventricle. Modified from Ho et al. (12).