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Fig. 3.13 Histology
(Weigert-Van Gieson stain)
(a) and
immunohistochemistry
(smooth muscle actin) (b) of
the wall of the ascending
aorta. Note the lamellar units
in the tunica media with
smooth muscle cells within
Fig. 3.14 The lamellar units
consist of elastic bers
(Elastin), encompassing
smooth muscle cells (VSMC)
and extracellular matrix
(ECM). From El-Hamamsy I,
Yacoub MH, Nature Reviews
Cardiology, 2009
G. Thiene and S. Rizzo
Mitral Valve
A. Anulus
B. Orifice
C. Leaflets
D. Chordae tendineae
E. Papillary muscles
F. Left ventricle
membranulis quatuor orificiorum cordis – The 11
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Mitral Valve
The mitral valve is a complex apparatus consisting of annulus, orice, leaets, chordae tendineae, and papillary muscles (Fig. 3.15). Moreover, the left ventricular free wall,
where the papillary muscles are implanted, should be
regarded as an intrinsic part of the mitral valve apparatus.
The origin of the name “mitral” is attributed to Andreas
Vesalius, who, in De Humani Corporis Fabrica, published in
1543, stated “one could not inappropriately compare to a
Bishop miter” (Fig.3.16).
Figure 9 Book VI
15
...mitrae episcopali non
admodum inepte
contuleris....
One could not
inappropriately compare
[these membranes] to a
Bishop miter
(a) The mitral annulus is an atrioventricular circular brous
structure where both left atrial and left ventricular myocardial free wall are attached (Fig.3.17). It represents a
barrier preventing electrical connection between the
atria and ventricles, aside the specialized atrioventricular conduction system of Tawara.
attachment of the posterior (mural) leaet of the mitral
valve, while the anterior leaet is in brous continuity
with the posterior noncoronary cusp of the aortic valve
and with the right and left brous trigons (Fig. 3.18).
The brous mitral annulus is thicker than that of the tricuspid valve.
the progressive rise of the pulmonary arterial pressure,
this phenomenon does not occur in the left side where
myocardial hypertrophy, secondary to systemic hypertension, reinforces the sphincteric contraction at the
annulus, maintaining mitral valve competence.
(b) The mitral orice is the passage of blood between the
leaets, which opens during ventricular diastole with
atrial systole and closes during ventricular systole and
atrial diastole. The nearing of the leaets during ventricular systole contributes to the closure of the orice,
by 20% of which is ascribable to a sphincteric contraction of the annulus (Fig.3.19). Occlusion of the mitral
Fig. 3.15 The mitral valve apparatus consists of leaets, annulus, orice, chordae tendineae, papillary muscles, and left ventricular wall
(PM posteromedial; AL anterolateral)
An evident brous annulus is present only at the
Whereas tricuspid valve regurgitation increases with
Andreas Vesalius, De Humani corporis fabrica,
1543, Book VI, Chapter XIII (De undecim
membranes of the heart’s four orifices), p. 592.
Fig. 3.16 Picture from the book of Andreas Vesalius: the name
“mitral” derives from the bishop’s miter
orice may occur in peculiar situations as in case of ball
thrombus or a myxoma in the left atrium (see mitral
pathology).
(c) Leaets: Basically there are two leaets, one anterior
and one posterior (Fig.3.20). This is the reason why the
mitral valve is considered “bicuspid” when compared to
the “tricuspid” right atrioventricular valve. However, the
posterior (mural) leaet generally shows three scallops,
so the mitral valve should be considered as a quadricuspid structure. The three scallops are particularly evident
in mitral valve prolapse (see pathology of mitral valve
chapter).
The anterior leaet is deep and narrow, whereas the
posterior one is large and less deep, in so far as the area
of the two is equal, which means that they equally share
the closure of the orice during ventricular systole
(Fig.3.20).
Both anterior and posterior leaets show a rough
zone on their ventricular side where second-order chordae tendineae insert (Figs.3.18 and 3.20).
(d) Chordae tendineae: These are brous tendons that arise
from the top of the papillary muscles, branch twice, and
reach the leaets to ensure the excursion and an adequate approximation during ventricular systole.
The classication of Roberts-Perloff is perhaps the
most useful from the pathophysiological view point; 20
to 25 chordae tendineae (“rst-order” chordae) take origin from the top of the papillary muscles, divide in
“second- order,” and nally attach to the leaets in the
“third order” chordae (Fig.3.21).
Another classication refers to the site where the
chordae tendineae connect to the leaets: “rst-order”
chordae insert into the free margin, “second-order” into
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G. Thiene and S. Rizzo
Fig. 3.17 A ring of the mitral
valve (a) does exist only in
correspondence of the
posterolateral (mural) leaet
(b)
Fig. 3.18 The mitral valve
belongs to the left ventricle,
without any relationship with
the ventricular septum (a).
Schematic representation (b)
b
a
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Fig. 3.19 The sphincteric
contraction of the annulus (a)
contributes by 20% of the
orice closure during
ventricular systole (b)
a
17
b
Fig. 3.20 The shape of the mitral leaets (a) is different; however, the
size is equal (b). A, P=anterior, posterior leaets. AL, PM=anterior
and posterior papillary muscle
Fig. 3.21 Roberts-Perloff classication of the chordae tendineae
according to branching
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G. Thiene and S. Rizzo
the rough zone on the ventricular side of the leaet, 1–2
centimeters from the free margin (Fig.3.22). Among the
“second-order” chordae to the anterior leaet, there are
long thick tendons (“strut chordae”), playing the important role to cope with the systolic strain (Fig. 3.23).
“Third-order” chordae tendineae are present in the posterior leaet, arising from minute papillary muscles or
directly from the endocardium to insert to the basal part
of the leaet, quite close to the annulus (Fig.3.22).
Fig. 3.22 View of the various orders of chordae tendineae according to
the site of insertion: 1=rst order, free margin; 2=second order, rough
zone; 3=third order, base of the mural, posterolateral brous ring
“First-order” chordae inserting at the commissures
exhibit a peculiar shape (“fan-like chordae”) (Fig.3.24).
At histology, the leaets show three layers (Fig.3.25):
(a) A thick brosa, facing the ventricle and made by colla-
gen bundles. The chordae tendineae insert directly to the
cusp brosa and are also made exclusively by collagen
(Fig.3.26).
(b) A thin auricularis consisting of a broelastic
component.
(c) A spongiosa in between, made by extracellular matrix,
mostly ground substance.
(e) Papillary muscles: There are two main papillary muscles
of the mitral valve—the anterolateral and the posteromedial (Fig.3.20). They arise from the free wall of the left
ventricle without any relationship with the ventricular
septum (Fig.3.18).
The anterolateral is a single pillar, giving origin to
chordae tendineae for both the leaets. The posteromedial consists of a group of stems (Fig.3.17), from which
originate several chordae including “fan-like” chordae
inserting into the commissures of the scallops (Fig.3.20).
Blood supply to the anterolateral papillary muscle is
provided by a diagonal branch of the anterior descending coronary artery. The posteroseptal group of papillary
muscles are perfused by the dominant coronary artery,
most frequently by the right coronary or the left
circumex.
Fig. 3.23 (a) View of the
mitral valve and left ventricle.
(b) Note a strut chorda to the
anterior leaet and mitroaortic brous continuity. Ao =
aorta; cf = brous continuity;
A = anterior leaet; P =
posterior leaet; * = strut
chordae
a b
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Fig. 3.24 Fan-like commissural chordae, all attaching to the free margin (“rst order”)
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a
b
Fig. 3.26 The chordae tendineae consists of collagen bers and connect with the brosa. (a) Azan Mallory stain, (b) Weigert-Van Gieson
stain
a
b
Fig. 3.25 The three layers of an av valve leaet: a thick brosa (collagen), facing the ventricle, a thin broelastic fascicular facing the
atrium, and a spongiosa in between (consisting of ground substance).
Note the chordae tendineae attaching to the brosa. (a) Azan Mallory
stain, (b) Weigert-Van Gieson stain
Tricuspid Valve
Moreover, the right atrioventricular valve is a ventricular
structure, consisting of three leaets (“tricuspid”) (septal,
anterior, and posterior), orice, annulus, chordae tendineae,
papillary muscles, and ventricular wall as a platform of papillary muscles attached to the right ventricular free wall and
septum (Figs.3.27 and 3.28).
The brous annulus separates the right atrium from the
right ventricle. The right ventricular free wall is thinner than
that of the left ventricle (Fig.3.28). This explains why tricuspid valve incompetence occurs frequently in pulmonary
hypertension as a consequence of annular dilatation. In addition, the degree of sphincteric contraction of the tricuspid
annulus is much less than that of the mitral valve, being the
atrial and ventricular walls thinner than the left-sided structures (Fig.3.29).
Unlike the mitral valve, the tricuspid valve is attached
with its septal leaet to the ventricular septum (Figs.3.28,
3.30 and 3.31). Moreover, the moderator band joins the sep-
tomarginal trabecula to the anterior papillary muscle
(Fig.3.32).
The septal leaet is attached to the septum by small papillary muscles or directly through chordae tendineae
(Figs.3.28, 3.30 and 3.31) and to the septal annulus of the
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G. Thiene and S. Rizzo
a
b
LPM
APM
IPM
Fig. 3.27 Open tricuspid valve (a). Unlike mitral valve, the septal leaf-
let of tricuspid valve is attached to the ventricular septum by small papillary muscles or directly by chordae tendineae (b). APM anterior
papillary muscle; IPM inferior papillary muscle; LPM Lancisi papillary
muscle
atrioventricular junction, from the anteroseptal to the posteroseptal commissures (Fig.3.27). The former is just close
of the membranous septum (Fig.3.28) and consists of fanlike chordae tendineae originating from the conal (“Lancisi”)
papillary muscle which is implanted on the pulmonary infundibulum (Fig.3.32).
The posteroseptal commissure is marked by chordae tendineae originating from a group of posterior papillary muscles (Figs.3.27 and 3.31).
The anterior tricuspid leaet is a large curtain from the
anteroseptal to the anteroposterior commissures. The anterior papillary muscle is a big pillar from the top of which
chordae tendineae arise connecting by branching both anterior and posterior leaets, the base of which is attached to the
atrioventricular ring of the anterior free wall (Figs.3.32 and
3.33).
Roughly, by external view the acute margin of the heart
corresponds to the commissure in between the anterior and
posterior leaets (anteroposterior commissure of the tricuspid valve) (Fig.3.31).
Moreover, the tricuspid valve commissures are the conuence between the leaets where the distance from the atrioventricular ring is shorter. Usually, the cusps show continuity
with the exception of the anteroseptal commissure where
discontinuity is observed in 10–20% of cases (Fig.3.31). In
Fig. 3.28 Comparison of
right (a) vs left (b)
atrioventricular ring. The right
one is tiny. Note also that the
right ventricular mass
attaching to the av ring is
thinner than the left one
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Fig. 3.29 (a) Right side of
the ventricular septum, to
which the septal leaet of the
tricuspid valve is directly
attached. (b) Drawing of the
trabecula septomarginalis
(TSM) connected to the
anterior papillary muscle by
moderator band
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Fig. 3.30 Open right ventricle and view of the tricuspid valve with
anterior, septal, and posterior leaets. Note fan-like chordae, arising
from the conal (“Lancisi”) muscle and branching to the anteroseptal
commissure. The septal leaet is split in correspondence of the membranous septum
Fig. 3.31 View of the pulmonary infundibulum (right ventricular outow track) with the anterior leaet of the tricuspid valve and marginal
band linking the trabecula septomarginalis to the anterior papillary
muscle
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Fig. 3.32 View of conal (“Lancisi”) muscle, trabecula septomarginalis, anterior papillary muscle, and anterior leaet of the tricuspid valve
G. Thiene and S. Rizzo
At histology, the leaets, like those of the mitral valve,
show three layers: a thick brosa, made by collagen bundles
and facing the right ventricle, to which the chordae tendineae
are connected and made of collagen bundles; a thin auricularis facing the atrium and consisting of bro-elastic bers;
and a spongiosa in between, mostly made by ground substance extracellular matrix.
Pulmonary Valve
Similar to the aortic valve, the pulmonary valve apparatus also
consists of cusps, commissures, interleaet triangles, and pulmonary artery (Fig. 3.34). The pulmonary valve has three
cusps: two posterior, facing the aortic root, and one anterior.
The shape of the cusps is semilunar with a swallow nest
shape.
The pulmonary valve differs from the aortic one for several structural features:
(a) The pulmonary artery is anterior and it takes origin from
the right ventricle.
(b) There are no coronary ostia.
(c) All the cusps lie over the infundibular myocardium. At
variance with the mitral valve, no brous continuity
exists between the anterior tricuspid leaet and the pos-
terior pulmonary right semilunar cusp, since the crista
superventricularis is wedged between the tricuspid and
pulmonary valves (Figs.3.35, 3.36 and 3.37).
Fig. 3.33 The close relationship between the His bundle, membranous
septum, and anteroseptal commissure of the tricuspid valve
the latter condition, the underlying membranous septum
appears bare on the posteroinferior aspect where the His
bundle runs (Fig.3.33).
The chordae tendineae of the tricuspid valve do not differ
from those of the mitral valve, including the presence of fanlike chordae at the commissural level (Fig.3.31).
Fig. 3.34 Normal pulmonary valve with three semilunar, swallow
nest-like cusps. The pulmonary artery arises from the ventricular outow tract (pulmonary infundibulum). Note the crista supraventricularis
separating tricuspid and pulmonary valves. Look at the conal (“Lancisi”)
papillary muscle
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Fig. 3.35 The pulmonary
valve seen from below. (a) It
lies over the ventricular
myocardium, at difference
from the aortic valve (b),
which is in brous continuity
with the anterior leaet of the
mitral valve
Fig. 3.36 Comparison
between right (a) and left (b)
ventricular outows. Unlike
anterior leaet of the mitral
valve, which is in brous
continuity with the aortic
valve (b), the anterior leaet
of the tricuspid valve shows
muscular discontinuity with
the pulmonary valve, because
of crista supraventricularis (a)
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