Thorax

1. HEART
CHAMBERS
Dr M Idris Siddiqui

2. The heart
• The Heart is a hollow muscular organ situated in
the mediastinum of the thoracic cavity, enclosed in
the pericardium.
• It is somewhat pyramidal in shape and placed
obliquely behind the sternum and adjoining parts
of costal cartilages so that 1/3rd of the heart is to
the right of median plane and 2/3rd of the heart is
to the left of the median plane.

4. The heart
• The heart is composed of 4 chambers :–
– Right atrium,
– Right ventricle,
– Left atrium,
– Left ventricle.
• Blood returning to the heart enters the atria, and is
then pumped into the ventricles.
• From the left ventricle, blood passes into the aorta
and enters the systemic circulation.
• From the right, it enters the pulmonary
circulation via the pulmonary arteries.

5. Cardiac chambers
• The 2 atrial chambers are divided from every other by a
vertical septum the interatrial septum and the 2 ventricular
chambers are divided from every other by a vertical septum
the interventricular septum.
• Interatrial septum is set obliquely from front to back & to the
right so that
– A. Right atrium lies in front & to the right.
– B. Left atrium lies behind & to the left.
• The right atrium interacts with the right ventricle via right
atrioventricular orifice, that is guarded by 3 cusps.
• The left atrium interacts with all the left ventricle via the left
atrioventricular orifice, that is guarded by 2 cusps.
• The atria are thin walled as compared to the ventricles and
have little contractile power.

6. DEMARCATION OF CHAMBERS OF THE
HEART ON THE SURFACE
• On the surface the chambers of the heart
are demarcated or delineated by the
following 3 grooves:
• A. Coronary sulcus (atrioventricular
groove).
• B. Anterior interventricular sulcus.
• C. Posterior interventricular sulcus.

7. CORONARY SULCUS (ATRIOVENTRICULAR GROOVE)
• It encircles the heart and separates
the atria from the ventricles.
• It is deficient anteriorly because of
the root of pulmonary trunk.
• The atrioventricular groove is split
into anterior and posterior parts.

8. CORONARY SULCUS
• THE ANTERIOR PART IS COMPOSED OF LEFT AND
RIGHT HALVES
• The right half of the anterior part runs downwards
and to the right between the right atrium and right
ventricle and lodges right coronary artery.
• The left anterior part of AV groove intervenes
between the left auricle and left ventricle. It lodges
circumflex branch of left coronary artery.
• The posterior part of AV groove intervenes
between the base and the diaphragmatic surface
of the heart. It lodges coronary sinus.

9. ANTERIOR AND POSTERIOR INTERVENTRICULAR SULCI
• They separate the left and right ventricles.
• The anterior interventricular sulcus is on the
sternocostal surface of the heart and lodges anterior
interventricular artery and great cardiac vein.
• The posterior interventricular groove is on the
diaphragmatic surface and lodges posterior
interventricular artery and middle cardiac vein.
• The meeting point of interatrial groove, posterior
interventricular groove, and posterior part of
atrioventricular groove is referred to as crux of the
heart.

11. Right Atrium
• The right atrium receives deoxygenated blood from the
superior and inferior vena cavae, from the coronary veins &
from the vene cordae minimae.
• It pumps this blood through the right atrioventricular
orifice(guarded by the tricuspid valve) into the right ventricle.
• The right atrium is somewhat quadrilateral chamber situated
behind and to the right side of the right ventricle. It is
composed of a main cavity and a small outpouching named
auricle.
• In the anatomical position, the right atrium forms the right
border of the heart.
• Extending from the antero-medial portion of the chamber is
the right auricle (right atrial appendage).
– A muscular pouch that acts to increase the capacity of the atrium.

12. The right atrium
• EXTERNAL FEATURES
• A. The right atrium is elongated vertically and gets superior vena
cava (SVC) at its upper end and the inferior vena cava(IVC) at its lower
end.
• B. The upper anterior part is prolonged to the left to create the right
auricular appendage, the right auricle. The margins of the auricle are
notched. The right auricle overlaps the roots of the
ascending aorta completely and infundibulum of the right ventricle
partly.
• C. A shallow vertical groove referred to as sulcus terminalis extends
along the right border between the superior and inferior vena cavae.
The upper part of the sulcus includes the sinuatrial (SA) node. Internally
it corresponds to crista terminalis.
• D. The vertical right atrioventricular groove lodges the right coronary
artery and the small cardiac vein.

14. INTERNAL FEATURES
right atrium
• The interior of the right atrium is split into 2 parts:
• A. Main smooth posterior part – the sinus
venarum, and.
• B. Rough anterior part – the atrium proper. The two
parts are separated from every other by crista
terminalis.
• The coronary sinus receives blood from the
coronary veins. It opens into the right atrium
between the inferior vena cava orifice and the right
atrioventricular orifice.
• Septal wall of the right atrium

15. Septal wall of the right atrium
• Developmentally it is originated from septum primum and septum
secundum. The septal wall inside presents the following features:
• A. Fossa ovalis, a shallow oval/saucer-shaped depression in the lower
part, created by septum primum.
– It represents the site of foramen ovale in the foetus.
• B. Annulus ovalis/limbus fossa ovalis, creates the distinct upper and
lateral margin of the fossa ovalis.
– It represents the free edge of the septum secundum. Inferiorly the annulus ovalis is
continuous with the left end of the valve of IVC.
• C. Triangle of Koch, a triangular area bounded in front by the base of
septal leaflet of tricuspid valve, behind by anterior margin of the
opening of coronary sinus and above by the tendon of Todaro- a
subendocardial ridge.
– The atrioventricular node is located in this triangle.
• D. Torus aorticus, an elevation in the anterosuperior part of the septum
produced due to bulging of the non-coronary sinus of ascending aorta.

17. DIFFERENCES BETWEEN THE SMOOTH AND
ROUGH PARTS OF THE RIGHT ATRIUM
Smooth part (sinus venarum) Rough part (atrium proper)
Developmentally it is derived from
right horn of the sinus venosus
Developmentally it is derived from
primitive atrium
All the venous channels except
anterior cardiac veins open into
this part (e.g., SVC, IVC, coronary
sinus, and venae cordae minimi)
Presents series of transverse
ridges, the musculipectinati, which
arise from the crista terminalis and
run forwards towards the auricle.
The interior of auricle presents
reticular sponge-like network of
the muscular ridges

21. CLINICAL SIGNIFICANCE
• The sponge-like interior of right auricle
prevents the free blood flow and thus favors
the formation of thrombus. The thrombi may
dislodge during auricular fibrillation and can
cause pulmonary embolism.

22. OPENING INTO THE RIGHT ATRIUM
• A. Opening of SVC: The SVC opens at the upper end of the right atrium
and has no valve. It returns the blood to the heart from the upper half
of the body.
• B. Opening of IVC: The IVC opens at the lower end of the right atrium
near the interatrial septum. It is guarded by a rudimentary non-
functioning semilunar valve referred to as valve of the inferior vena
cava/Eustachian valve.
• C. Opening of coronary sinus: The coronary sinus, which drains the
majority of the blood from the heart, opens into the right atrium
between the openings of IVC and right atrioventricular orifice. It is also
guarded by a rudimentary non-functioning valve, Thebesian valve.
• D. Right atrioventricular(tricuspid)orifice (largest opening): It interacts
the right atrial chamber with all the right ventricular chamber. It is
located anterior to the opening of IVC and is guarded by the tricuspid
valve.
• E. Many small orifices of small veins: These are the opening of venae
cordisminimae (Thebesian veins) and anterior cardiac veins.
– During embryonic life, the Eustachian valve guides the blood of IVC to the left atrium via foramen ovale. A very small projection
termed intervenous tubercle (of Lower) is scarcely visible on the posterior wall of the right atrium just below the opening of SVC.
During embryonic life it directs the blood of SVC to the right ventricle

23. Interatrial Septum
• The interatrial septum is a solid muscular wall that
separates the right and left atria.
• The septal wall in the right atrium is marked by a
small oval-shaped depression called
the fossa ovalis.
• This is the remnant of the foramen ovale in the
foetal heart, which allows right to left shunting of
blood to bypass the lungs.
• It closes once the newborn takes its first breath.

24. Atrial Septal Defect
• An atrial septal defect is an abnormal opening in the
interatrial septum, persistent after birth. The most
common site is the foramen ovale, and this is known as
a patent foramen ovale.
• In the adult, left atrial pressure is usually greater than
that of the right atrium, so blood is shunted through
the opening from left to right. In large septal defects,
this can cause right ventricular overload, leading to
pulmonary hypertension, right ventricular hypertrophy
and ultimately right heart failure.
• Definitive treatment is closure of the defect by surgical
or transcatheter closure.

25. Left Atrium
• The left atrium receives oxygenated blood from the
four pulmonary veins, and pumps it through the left
atrioventricular orifice (guarded by the mitral valve) into the
left ventricle.
• In the anatomical position, the left atrium forms
the posterior border (base) of the heart.
• The left auricle extends from the superior aspect of the
chamber, overlapping the root of the pulmonary trunk.
• The interior surface of the left atrium can be divided into two
parts, each with a distinct embryological origin:
• Inflow portion – receives blood from the pulmonary veins. Its
internal surface is smooth and it is derived from the
pulmonary veins themselves.
• Outflow portion – located anteriorly, and includes the left
auricle. It is lined by pectinate muscles, and is derived from
the embryonic atrium.

28. EXTERNAL FEATURES
left atrium
• A. It is a thin-walled quadrangular chamber situated
posteriorly behind and to the left side of right
atrium. It creates greater part (left 2/3rd) of the
base of the heart.
• B. Its upper end is prolonged anteriorly to create
the left auricle, which overlaps the infundibulum of
right ventricle.
• C. Behind the left atrium is located:
– (a) Oblique sinus of serous pericardium
– (b) Fibrous pericardium, which separates it from
the esophagus.

29. Relations of the left atrium
to
transverse & oblique sinuses
• The left atrium lies behind:
– The ascending aorta & the pulmonary trunk
• (the anterior wall is separated from these two structures by
the transverse sinus of the pericardium)
• The left atrium lies in front of :
– The descending aorta and the esophagus.
• ( the posterior wall is separated from these two structures by
the oblique sinus of the pericardium)

30. INTERNAL FEATURES
of left atrium
• A. The interior of left atrium is smooth,
but the left auricle possesses muscular
ridges in the form of reticulum.
• B. The anterior wall of left atrial cavity
presents fossa lunata, which
corresponds to the fossa ovalis of the
right atrium.

31. OPENINGS IN THE LEFT ATRIUM
• Openings in the left atrium are as follows:
• A. Openings of 4 pulmonary veins in its
posterior wall, 2 on every side. They have
no valves.
• B. Number of small openings of venae
cordis minimae.
• C. Left atrioventricular orifice. It is guarded by
the mitral valve

32. Right Ventricle
• The right ventricle receives deoxygenated blood
from the right atrium, and pumps it through the
pulmonary orifice (guarded by the pulmonary
valve), into the pulmonary artery.
• It is triangular in shape, and forms the majority of
the anterior border of the heart.
• The right ventricle can be divided into an inflow and
outflow portion, which are separated by a muscular
ridge known as the supraventricular crest.

33. Inflow Portion of Right Ventricle
• The interior of the inflow part of the right ventricle is covered
by a series of irregular muscular elevations, called trabeculae
carnae. They give the ventricle a ‘sponge-like’ and is of three
main types:
• Ridges – attached along their entire length on one side to
form ridges along the interior surface of the ventricle.
• Bridges – attached to the ventricle at both ends, but free in
the middle. The most important example of this type is the
moderator band, which spans between the interventricular
septum and the anterior wall of the right ventricle.
• Pillars (papillary muscles) – anchored by their base to the
ventricles. Their apices are attached to fibrous cords (chordae
tendineae), which are in turn attached to the three tricuspid
valve cusps.

34. PAPILLARY MUSCLES of RIGHT VENTRICULAR CHAMBER
These represent the pillars of trabeculae carneae.
The papillary muscles project inwards. Their bases
Are connected to the ventricular wall and their apices
Are connected by thread-like fibrous cords (the
Chordae tendinae) to the cusps of the tricuspid valve.
There are 3 papillary muscles in the right ventricle:
– (a) Anterior , it is the largest
– (b) Posterior (inferior),it is small
– (c) Septal , it is generally split into 2 or 3 nipples. The
papillary muscles of right ventricle are connected to the
cusps of the tricuspid valve

35. Outflow Portion of right ventricle
(Conus arteriosus or infundibulum)
• It is derived from the embryonic bulbus cordis.
• The outflow portion (leading to the
pulmonary artery) is located in the superior
aspect of the ventricle.
• It is visibly different from the rest of the right
ventricle, with smooth walls and no
trabeculae carneae.

39. Right ventricle
• The right ventricle is the thick-walled triangular
chamber of the heart which interacts with the right
atrium via right atrioventricular orifice and with the
pulmonary trunk via pulmonary orifice.
• EXTERNAL FEATURES
• A. It creates the majority of sternocostal surface
and small part of the diaphragmatic surface of the
heart. It also creates the inferior border.
• B. It is divided from the right atrium by a more or
less vertical anterior part of the coronary sulcus/
atrioventricular groove

44. DIFFERENCES OF INFLOWING AND
OUTFLOWING PARTS OF THE RIGHT VENTRICLE
Inflowing lower part Outflowing upper part
It develops from primitive ventricle It develops from bulbus cordis
It is large in size and lies below the
supraventricular crest
It is small in size and lies above the
supraventricular crest
It is rough due to presence of It is
smooth and forms upper 1 the
muscular ridges—the inch conical
part of the right trabeculae
carneae.
It forms ventricular chamber—the
most of the right ventricular
infundibulum, which gives rise
chamber to pulmonary trunk

45. INTERNAL FEATURES
of right ventricle
• A. The interior of right ventricle is composed of 2 parts:
– (a) A large, lower rough inflowing part, and
– (b) A small upper outflowing part, the infundibulum.
• The 2 parts are divided from every other by a muscular
ridge, the supraventricular crest (infundibuloventricular
crest).
• B. The cavity of right ventricle is flattened by the
forward bulge of the interventricular septum. In
transverse section it is crescent shaped.
• C. The wall of the right ventricle is thinner than that of
the left ventricle (ratio 1:3).

48. Moderator Band (Septomarginal trabeculum)
• It is thick muscular ridge extending from
ventricular septum to the base of the
anterior papillary muscle, across the
ventricular cavity.
• It conveys the right branch of the
atrioventricular bundle (bundle of His), a part
of conducting system of the heart.
• It prevents the over distension of right
ventricle.

51. Interventricular septum
• Membranomuscular partition between the two
ventricles, obliquely placed, and is composed of:
– The inferior muscular part forms the majority of the
septum and is the same thickness as the left ventricular
wall.
– Upper part of the septum is membranous, thinner, and
connects to the fibrous skeleton of the heart. Oval in
shape, of thumbnail size, it is of two types:
• Atrioventricular
• Interventricular

55. FEATURES OF
INTERVENTRICULAR SEPTUM
• Because obliquely placed to the left and slightly inferiorly
from posterior to anterior, the right ventricle tends to be
located anteriorly and the left ventricle posteriorly .
• It tends to bulge into the chamber of the right ventricle and
creates an indentation on the left ventricular side.
• The septum becomes thinner as well as more fibrous near
the aortic valve orifice under the margins of the right and
posterior leaflets.
– This region is termed the membranous part of the interventricular
septum. It is oval in shape.
• The muscular and membranous portions of the
interventricular septum have different developmental origins.
The membranous part of the septum is the most frequent
location for congenital ventricular septal defects.

56. Blood supply
of
INTERVENTRICULAR SEPTUM
• Posterior 2/3rd :
–Septal branches of posterior/inferior branch
of right coronary artery
• Anterior 1/3rd :
–Septal branch of anterior interventricular
branch of left coronary artery

57. Left Ventricle
• The left ventricle receives oxygenated blood from the left
atrium, and pumps it through the aortic orifice (guarded by
the aortic valve) into the aorta.
• In the anatomical position, the left ventricle forms the apex of
the heart, as well as the left and diaphragmatic borders.
Much like the right ventricle, it can be divided into an inflow
portion and an outflow portion.
• Inflow Portion
• The walls of the inflow portion of the left ventricle are lined
by trabeculae carneae, as described with the right ventricle.
There are two papillary muscles present which attach to the
cusps of the mitral valve.
• Outflow Portion
• The outflow part of the left ventricle is known as the aortic
vestibule. It is smooth-walled with no trabeculae carneae,
and is a derivative of the embryonic bulbus cordis.

59. The left ventricle
• The left ventricle is thick-walled
triangular chamber of the heart which
interacts with all the left atrium via left
atrioventricular orifice and with the
ascending aorta via aortic orifice.
• The walls of left ventricle are 3 times
thicker than that of the right ventricle.

60. The left ventricle
EXTERNAL FEATURES
The left ventricle creates the
(a) Apex of the heart,
(b) Small part of the sternocostal surface,
(c) Majority of the (left 2/3rd) diaphragmatic surface,
(d) The majority of the left border of the heart.
INTERNAL FEATURES
The interior of the left ventricle is split into 2 parts:
(a) A large lower rough inflowing part, and
(b) A small upper smooth outflowing part the aortic vestibule.
The cavity of the left ventricle is circular in cross section
since the interventricular septum bulges into the right
ventricle.

61. DIFFERENCES BETWEEN THE INFLOWING AND
OUTFLOWING PARTS OF THE LEFT VENTRICLE
Inflowing part Outflowing part
It develops from primitive ventricle It develops from bulbus cordis
It lies below the aortic vestibule It lies between the membranous
part of the interventricular septum
and anterior cusp of the mitral
valve
It is rough due to presence It is
smooth and forms smooth of
trabeculae carneae and small
upper part
The aortic forms most of the left
vestibule, which gives rise to the
ventricular chamber ascending
aorta
—

62. TRABECULAE CARNEAE OF LEFT VENTRICLE
• The trabeculae carneae of the left ventricle
are quite similar to those of the right
ventricle but are well developed and present
2 large papillary muscles (anterior and
posterior) and no moderator band.
• The papillary muscles of the left ventricle are
connected to the cusps of the mitral valve by
chordae tendinae.

63. OPENINGS IN THE LEFT VENTRICLE
• The openings in the left ventricle
are as follows:
• A. Left atrioventricular orifice.
• B. Aortic orifice.

64. Right ventricle Left ventricle
Receives deoxygenated blood from right
atrium and pumps it to the lungs through
pulmonary trunk
Receives oxygenated blood from left atrium
and pumps it to the whole body through aorta
Upper & anterior part is called infundibulum or
conus arteriosus
Upper & anterior part is called aortic vestibule
Wall of right ventricle is thinner than that of
left ventricle (ratio 1:3) 9mm
Wall of left ventricle is thicker than that of
right ventricle (ratio 3:1) 27mm
Possesses three papillary muscles (anterior,
posterior, and septal)
Possesses two papillary muscles (anterior and
posterior)
Moderator band present Moderator band absent
Cavity of right ventricle is crescentic in shape
in cross section
Cavity of left ventricle is circular in shape in
cross section
Outflow part is infundibulum Outflow part is aortic vestibule
Supraventricular crest separates inflow part
from outflow part
No such crest
Exit is pulmonary trunk Exit is aorta
Forms nearly whole of the lower border of
heart
Forms nearly whole left border of heart also
forms apex of heart

65. INTERVENTRICULAR SEPTAL DEFECT
• The most common congenital cardiac defect in infants,
but close before 10 years of age naturally.
• Almost 70% of ventricular septal deformities develop in
the membranous part of the septum, where a number
of embryonic tissues merge. Because the pressure of
the blood in the left ventricle is greater than that in the
right, this abrasion is initially related to left-to-right
acyanotic shunting of blood flow.
• The increased blood flow into the right ventricle
produces right ventricular hypertrophy, however, and
can lead to pulmonary hypertension, eventually
creating reversal of the shunt.
• Many of the mutations that cause atrial septal defects
can also result in ventricular septal defects.

67. Tetralogy of Fallot
• It is a cyanotic congenital heart disease, comprising four abnormalities as a
result of a single development defect.
• The four abnormalities are:
1. Ventricular septal defect
2. Overriding aorta (where the aorta is positioned directly over the VSD)
3. Pulmonary valve stenosis
4. Right ventricular hypertrophy
• Stenosis of the pulmonary valve increase the force needed to pump blood
through it, resulting in right ventricular hypertrophy. Eventually, the
pressure in the right ventricle becomes higher than that of the left – and
blood then shunts from right to left through the ventricular septal defect.
• The overriding aorta lies over the ventricular septal defect, resulting in
deoxygenated blood passing into the aorta.
– It is usually treated surgically in the first few months of life or in severe
cases, soon after birth.

72. Dextrocardia
• Sometimes the heart is malpositioned
with apex on the right side.
• This condition is named dextrocardia.
• It might be related to complete reversal
of thoracic and abdominal viscera, a
condition named situs inversus