Pericardium and Heart pdf - Thorax

CHAPTER 3

The Thorax: Part II—The Thoracic Cavity

Pericarditis

Pericardial fluid can be aspirated from the pericardial cavity

etrated. The blood escapes into the pericardial cavity and can

shot wounds when the chambers of the heart have been pen

heart during diastole. This compression of the heart is called

In inflammation of the serous pericardium, called pericarditis,

pericardial fluid may accumulate excessively, which can com-

press the thin-walled atria and interfere with the filling of the

cardiac tamponade.

Cardiac tamponade can also occur secondary to stab or gun-

restrict the filling of the heart.

Roughening of the visceral and parietal layers of serous peri-

cardium by inflammatory exudate in acute pericarditis produces
pericardial friction rub, which can be felt on palpation and heard

through a stethoscope.

should excessive amounts accumulate in pericarditis. This pro-

cess is called paracentesis. The needle can be introduced to the

left of the xiphoid process in an upward and backward direction

at an angle of 45° to the skin. When paracentesis is performed

at this site, the pleura and lung are not damaged because of the

presence of the cardiac notch in this area.

C L I N I C A L N O T E S

right common carotid artery

brachiocephalic artery

right subclavian artery

right

brachiocephalic vein

superior vena cava

transverse sinus

right pulmonary veins

reflection to left

atrium

inferior vena cava

fibrous pericardium

parietal layer of serous

pericardium

reflection of serous pericardium

left pulmonary vein

bronchus

left pulmonary artery

ligamentum arteriosum

left recurrent laryngeal nerve

left vagus nerve

left phrenic nerve

arch of aorta

left subclavian artery

left common carotid artery

left brachiocephalic vein

oblique sinus

FIGURE 3.32

The great blood vessels and the interior of the pericardium.

from each other by the vertical atrioventricular groove

right atrium and the right ventricle, which are separated

is formed mainly by the

sternocostal surface

The

(Fig. 3.34). The right border is formed by the right atrium;

It lies at the level of the fifth left intercostal space, 3.5 in.

directed downward, forward, and to the left (Fig. 3.34).

formed by the left ventricle, is

apex of the heart,

The

veins (Fig. 3.35). The base of the heart lies opposite the apex.

mainly by the left atrium, into which open the four pulmonary

or the posterior surface, is formed

base of the heart,

The

forms part of this surface.

right atrium, into which the inferior vena cava opens, also

terior interventricular groove. The inferior surface of the

mainly by the right and left ventricles separated by the pos

of the heart is formed

diaphragmatic surface

The

by the anterior interventricular groove.

cle. The right ventricle is separated from the left ventricle

the left border, by the left ventricle and part of the left auri-

(9 cm) from the midline. In the region of the apex, the apex
beat can usually be seen and palpated in the living patient.

Basic Anatomy

arch of aorta left common carotid artery

pulmonary trunk

left auricle

left coronary artery

circumflex branch

great cardiac vein

left ventricle

anterior
interventricular
artery

apex

interventricular groove

right ventricle

marginal
artery

atrioventricular
groove

anterior cardiac
vein

right
atrium

right coronary
artery

right auricle

ascending
aorta

right pulmonary
artery

superior vena cava

brachiocephalic
artery

left subclavian artery

ascending aorta

pulmonary trunk

(cut)

left auricle

right auricle

left

ventricle

right

ventricle

right

atrium

apex

superior vena cava

arch of aorta

(cut)

atrioventricular

groove

interventricular

groove

filled

with

fat

FIGURE 3.33

The anterior surface of the heart; the fibrous pericardium and the parietal serous pericardium have been

grooves. The coronary arteries are embedded in this fat.

removed. Note the presence of fat beneath the visceral serous pericardium in the atrioventricular and interventricular

FIGURE 3.34

The anterior surface of the heart and the great

the cardiac veins.

blood vessels. Note the course of the coronary arteries and

left common
carotid artery

left subclavian
artery

pulmonary
veins

left atrium

left ventricle

coronary sinus

inferior vena cava

right atrium

superior vena cava

bifurcation of pulmonary
trunk

ligamentum arteriosum

left recurrent laryngeal nerve

arch of
aorta

FIGURE 3.35

The posterior surface, or the base, of the heart.

CHAPTER 3

secundum (Fig. 3.37).

and the anulus is formed from the lower edge of the septum

the persistent septum primum of the heart of the embryo,

upper margin of the fossa. The floor of the fossa represents

in the fetus (Fig. 3.37). The anulus ovalis forms the

ovale

foramen

lis is a shallow depression, which is the site of the

right atrium from the left atrium (Fig. 3.36). The fossa ova

which separates the

atrial septum,

structures lie on the

These latter

anulus ovalis.

fossa ovalis

cava are the

In addition to the rudimentary valve of the inferior vena

Fetal Remnants

the heart and open directly into the right atrium.

Many small orifices of small veins also drain the wall of

valve (Fig. 3.36).

inferior vena caval opening and is guarded by the tricuspid

lies anterior to the

right atrioventricular orifice

The

fice. It is guarded by a rudimentary, nonfunctioning valve.

between the inferior vena cava and the atrioventricular ori

from the heart wall (Fig. 3.36), opens into the right atrium

which drains most of the blood

coronary sinus,

The

heart from the lower half of the body.

mentary, nonfunctioning valve. It returns the blood to the

the lower part of the right atrium; it is guarded by a rudi

(larger than the superior vena cava) opens into

vena cava

inferior

to the heart from the upper half of the body. The

part of the right atrium; it has no valve. It returns the blood

(Fig. 3.36) opens into the upper

superior vena cava

The

Openings into the Right Atrium

from the primitive atrium.

to the auricle. This anterior part is derived embryologically

which run from the crista terminalis

musculi pectinati,

is roughened or trabeculated by bundles of muscle fibers,

sinus venosus. The part of the atrium in front of the ridge

is smooth walled and is derived embryologically from the

The main part of the atrium that lies posterior to the ridge

crista terminalis.

which on the inside forms a ridge, the

sulcus terminalis,

the right auricle is a vertical groove, the

of the heart at the junction between the right atrium and

pouching, the auricle (Figs. 3.34 and 3.36). On the outside

The right atrium consists of a main cavity and a small out

Right Atrium

endocardium.

endothelium, the

and lined internally with a layer of

epicardium;

dium, the

covered externally with serous pericar

myocardium;

The walls of the heart are composed of cardiac muscle,

ventricle lies anterior to the left ventricle.

right atrium lies anterior to the left atrium, and the right

the right and left atria and the right and left ventricles. The

The heart is divided by vertical septa into four chambers:

when examining a radiograph of the heart.

the left ventricle. These borders are important to recognize

ventricle but also by the right atrium; the apex is formed by

(Fig. 3.34). The lower border is formed mainly by the right

border, by the left auricle; and below, by the left ventricle

The right border is formed by the right atrium; the left

matic (inferior) surface.

The heart does not rest on its base; it rests on its diaphrag

the heart is pyramid shaped; the base lies opposite the apex.

because

Note that the base of the heart is called the

The Thorax: Part II—The Thoracic Cavity

base

Borders of the Heart

Chambers of the Heart

the

and

superior vena cava

right auricle

sinuatrial node

crista terminalis

anulus ovalis

fossa ovalis

anterior wall of

right atrium

(reflected)

musculi pectinati

inferior vena cava

valve of inferior vena cava

valve of coronary sinus

chordae tendineae

septal cusp of

tricuspid valve

moderator band

right ventricle

interventricular

groove

left ventricle

right

branch of bundle

left

branch of bundle

atrioventricular bundle

infundibulum

left auricle

pulmonary trunk

ascending aorta

right coronary artery

atrioventricular node

FIGURE 3.36

Interior of the right atrium and the right ventricle. Note the positions of the sinuatrial node and the atrioventricu-

lar node and bundle.

Basic Anatomy

septum secundum

septum primum

foramen ovale

pulmonary stenosis

hypertrophy of
right ventricle

septal defect

displaced aortic
opening

left recurrent laryngeal
nerve

FIGURE 3.37

gus (Figs. 3.32 and 3.39).

and the fibrous pericardium separates it from the esopha

Behind it lies the oblique sinus of the serous pericardium,

base or the posterior surface of the heart (see Fig. 3.35).

behind the right atrium and forms the greater part of the

main cavity and a left auricle. The left atrium is situated

Similar to the right atrium, the left atrium consists of a

Left Atrium

and close the pulmonary orifice.

cusps fill, come into apposition in the center of the lumen,

flows back toward the heart and enters the sinuses; the valve

nary trunk by the outrushing blood. During diastole, blood

cusps of the valve are pressed against the wall of the pulmo

of unnecessary confusion.) During ventricular systole, the

rotated to the left. This, unfortunately, causes a great deal

according to their position in the fetus before the heart has

(The cusps of the pulmonary and aortic valves are named

rior (left cusp) and two anterior (anterior and right cusps).

The three semilunar cusps are arranged with one poste

aortic valve

(see

and one is situated external to each cusp

sinuses,

called the

cle. At the root of the pulmonary trunk are three dilatations

rial wall prevent the cusps from prolapsing into the ventri

cusps; the attachments of the sides of the cusps to the arte

chordae or papillary muscles are associated with these valve

cusps are directed upward into the pulmonary trunk. No

are attached to the arterial wall. The open mouths of the

enclosed. The curved lower margins and sides of each cusp

by folds of endocardium with some connective tissue

(Fig. 3.38A) and consists of three semilunar cusps formed

guards the pulmonary orifice

pulmonary valve

The

the adjacent parts of two cusps.

chordae tendineae of one papillary muscle are connected to

intraventricular pressure rises. To assist in this process, the

being forced into the atrium and turning inside out as the

the papillary muscles contract and prevent the cusps from

When the ventricle contracts,

papillary muscles.

to the

The chordae tendineae connect the cusps

dae tendineae.

chor

free edges and ventricular surfaces are attached to the

ring of the skeleton of the heart (see below), whereas their

inferiorly. The bases of the cusps are attached to the fibrous

ventricular septum, and the inferior or posterior cusp lies

rior cusp lies anteriorly, the septal cusp lies against the

(posterior) cusps. The ante

inferior

anterior, septal,

fold of endocardium with some connective tissue enclosed:

(Figs. 3.36 and 3.38) and consists of three cusps formed by a

guards the atrioventricular orifice

tricuspid valve

The

heart. The third type is simply composed of prominent ridges.

tricular bundle, which is part of the conducting system of the

the anterior wall. It conveys the right branch of the atrioven

crosses the ventricular cavity from the septal to

erator band,

mod

tricular wall, being free in the middle. One of these, the

(Fig. 3.36). The second type is attached at the ends to the ven

) to the cusps of the tricuspid valve

chordae tendineae

ventricular wall; their apices are connected by fibrous chords

which project inward, being attached by their bases to the

cles,

papillary mus

of three types. The first type comprises the

The trabeculae carneae are composed

trabeculae carneae.

the ventricular wall a spongelike appearance and are known

ridges formed of muscle bundles. The projecting ridges give

those of the right atrium and show several internal projecting

The walls of the right ventricle are much thicker than

dibulum.

funnel shaped, at which point it is referred to as the

As the cavity approaches the pulmonary orifice, it becomes

nary trunk through the pulmonary orifice (see Fig. 3.36).

through the atrioventricular orifice and with the pulmo

The right ventricle communicates with the right atrium

Right Ventricle

Coarctation of the aorta.

relationship to the left recurrent laryngeal nerve).

Patent ductus arteriosus (note the close

Tetralogy of Fallot.

Atrial septal defect.

Normal fetal heart.

infun-

(the

and

-
-

CHAPTER 3

The Thorax: Part II—The Thoracic Cavity

pulmonary
valve

tricuspid valve

aortic sinus

FIGURE 3.38

Fibrous skeleton

Path taken by the cardiac impulse from the sinuatrial node to the Purkinje network.

Path taken by the blood

Cross section of the ventricles of the heart.

Semilunar cusps of the aortic valve.

Mitral cusps with valve

Mitral cusps with valve open.

Position of the tricuspid and pulmonary valves.

closed. D.

through the heart. G.

of the heart.

right atrium

left atrium

middle lobe of
right lung

right oblique
fissure

lower lobe
of right lung

esophagus

azygos vein

thoracic
duct

sympathetic trunk

splanchnic nerves

hemiazygos vein

descending aorta

oblique sinus

pulmonary vein

lower lobe of
left lung

left oblique fissure

upper lobe of left lung

pericardium

pericardial cavity

left ventricle

right ventricle

sternum

FIGURE 3.39

Cross section of the thorax at the eighth thoracic vertebra, as seen from below. (Note that all computed tomog

raphy scans and magnetic resonance imaging studies are viewed from below.)

Basic Anatomy

The atrioventricular bundle (bundle of His) is the only

Atrioventricular Bundle

tricles before the ventricles start to contract.

ficient time for the atria to empty their blood into the ven

the atrioventricular node (about 0.11 seconds) allows suf

The speed of conduction of the cardiac impulse through

atrial myocardium.

stimulated by the excitation wave as it passes through the

by the atrioventricular bundle. The atrioventricular node is

From it, the cardiac impulse is conducted to the ventricles

the septal cusp of the tricuspid valve (Figs. 3.37 and 3.38).

lower part of the atrial septum just above the attachment of

The atrioventricular node is strategically placed on the

Atrioventricular Node

muscle of the atria and cause the muscle to contract.

impulses that spread in all directions through the cardiac

The node spontaneously gives origin to rhythmic electrical

the opening of the superior vena cava (Figs. 3.36 and 3.40).

in the upper part of the sulcus terminalis just to the right of

The sinuatrial node is located in the wall of the right atrium

Sinuatrial Node

that form the conducting system of the heart).

(specialized cardiac muscle fibers

Purkinje fibers

plexus of

its right and left terminal branches, and the subendocardial

atrioventricular bundle

atrioventricular node,

sinuatrial node,

ized cardiac muscle present in the

The conducting system of the heart consists of special

into the ventricles before the ventricles contract.

the ventricles allows time for the atria to empty their blood

slight delay in the passage of the impulse from the atria to

later by the contractions of both ventricles together. The

heart, so the atria contract first and together, to be followed

system and the impulse travels to different regions of the

tractile process originates spontaneously in the conducting

beats per minute in the resting adult. The rhythmic con

The normal heart contracts rhythmically at about 70 to 90

nuity between the atria and the ventricles.

skeleton of the heart forms the basis of electrical disconti

valves from stretching and becoming incompetent. The

rings support the bases of the valve cusps and prevent the

but provide attachment for the muscle fibers. The fibrous

the muscular walls of the atria from those of the ventricles

fibrous rings around the atrioventricular orifices separate

the membranous upper part of the ventricular septum. The

pulmonary, and aortic orifices and are continuous with

sists of fibrous rings that surround the atrioventricular,

(Fig. 3.38) con

skeleton of the heart

The so-called

nous and attached to the fibrous skeleton.

The smaller upper part of the septum is thin and membra

lower part of the septum is thick and formed of muscle.

by the anterior and posterior interventricular grooves. The

the left. Its position is indicated on the surface of the heart

ward and to the right and the other facing backward and to

The septum is placed obliquely, with one surface facing for

into the right and left ventricles.

(interventricular) septum

ventricular

the heart has thick walls and is divided by the

heart backward and to the right. The ventricular portion of

and left atria. The septum runs from the anterior wall of the

into the right

atrial (interatrial) septum

divided by the

atrial portion of the heart has relatively thin walls and is

epicardium and lined internally by the endocardium. The

diac muscle, the myocardium, covered externally by the

The walls of the heart are composed of a thick layer of car

the left coronary artery.

coronary artery, and the left posterior sinus gives origin to

The anterior aortic sinus gives origin to the right

tic sinus.

aor

Behind each cusp, the aortic wall bulges to form an

are located on the posterior wall (left and posterior cusps).

cusp is situated on the anterior wall (right cusp) and two

similar in structure to the pulmonary valve (Fig. 3.38). One

guards the aortic orifice and is precisely

aortic valve

The

the papillary muscles is similar to that of the tricuspid valve.

The attachment of the chordae tendineae to the cusps and

intervenes between the atrioventricular and aortic orifices.

of the tricuspid valve. The anterior cusp is the larger and

posterior, which have a structure similar to that of the cusps

(Fig. 3.38). It consists of two cusps, one anterior and one

guards the atrioventricular orifice

mitral valve

The

aortic vestibule.

aortic orifice is called the

but no moderator band. The part of the ventricle below the

developed trabeculae carneae, two large papillary muscles,

the cavity of the right ventricle (Fig. 3.38). There are well-

tic because of the bulging of the ventricular septum into

section, the left ventricle is circular; the right is crescen

times higher than that inside the right ventricle.) In cross

ventricle. (The left intraventricular blood pressure is six

(Fig. 3.38) are three times thicker than those of the right

through the aortic orifice. The walls of the left ventricle

through the atrioventricular orifice and with the aorta

The left ventricle communicates with the left atrium

Left Ventricle

valve.

The left atrioventricular orifice is guarded by the mitral

through the posterior wall (Fig. 3.35) and have no valves.

The four pulmonary veins, two from each lung, open

Openings into the Left Atrium

auricle possesses muscular ridges as in the right auricle.

The interior of the left atrium is smooth, but the left

Structure of the Heart

Conducting System of the Heart

the

and

-
-

band, where it crosses to the anterior wall of the right

side of the ventricular septum to reach the moderator

The right bundle branch (RBB) passes down on the right

tum, it divides into two branches, one for each ventricle.

tum. At the upper border of the muscular part of the sep

border of the membranous part of the ventricular sep

septal cusp of the tricuspid valve to reach the inferior

The atrioventricular bundle then descends behind the

dle descends through the fibrous skeleton of the heart.

travel from the atria to the ventricles (Fig. 3.40). The bun

thus the only route along which the cardiac impulse can

of the atria and the myocardium of the ventricles and is

pathway of cardiac muscle that connects the myocardium

-
-

CHAPTER 3

The Thorax: Part II—The Thoracic Cavity

sinuatrial
node

right atrium

internodal
pathways

right branch
of atrioventricular
bundle

Purkinje
plexus

left branch of
atrioventricular
bundle

atrioventricular
bundle

atrioventricular
node

FIGURE 3.40

The conducting system of the heart. Note the

the superior vena caval opening. It descends on the atrial

posterior end of the sinuatrial node and passes posterior to

leaves the

middle internodal pathway

tricular node. The

descends on the atrial septum and ends in the atrioven

and passes anterior to the superior vena caval opening. It

leaves the anterior end of the sinuatrial node

pathway

anterior internodal

ordinary cardiac muscle cells. The

a structure consisting of a mixture of Purkinje fibers and

special pathways in the atrial wall (Fig. 3.40), which have

phenomenon has been explained by the description of

can travel by passing along the ordinary myocardium. This

travel to the atrioventricular node more rapidly than they

Impulses from the sinuatrial node have been shown to

Internodal Conduction Paths

have the opposite effect.

rate of conduction of the impulse; the sympathetic nerves

parasympathetic nerves slow the rhythm and diminish the

enced by the autonomic nerve supply to the heart. The

The activities of the conducting system can be influ

chambers contract in a coordinated and efficient manner.

throughout the myocardium of the heart so that the different

impulses, but also for conducting these impulses rapidly

is responsible not only for generating rhythmic cardiac

It is thus seen that the conducting system of the heart

Purkinje plexus of the left ventricle.

which eventually become continuous with the fibers of the

usually divides into two branches (anterior and posterior),

passes down on its left side beneath the endocardium. It

The left bundle branch (LBB) pierces the septum and

the Purkinje plexus (Fig. 3.40).

ventricle. Here, it becomes continuous with the fibers of

internodal pathways.

Failure of the Conduction System of the Heart

likely to occur if the blow occurs during the upstroke of the T

the young is most likely due to the compliant chest wall due

mic contraction of the ventricles (arrhythmias) or, if complete

spread from the atria to the ventricles. Failure of the bundle to

The sinuatrial node is the spontaneous source of the cardiac

impulse. The atrioventricular node is responsible for picking

up the cardiac impulse from the atria. The atrioventricular

bundle is the only route by which the cardiac impulse can

conduct the normal impulses results in alteration in the rhyth-

bundle block occurs, complete dissociation between the atria

and ventricular rates of contraction. The common cause of

defective conduction through the bundle or its branches is

atherosclerosis of the coronary arteries, which results in a

diminished blood supply to the conducting system.

Commotio Cordis

This condition results in ventricular fibrillation and sudden

death and is caused by a blunt nonpenetrating blow to the

anterior chest wall over the heart. It occurs most commonly

in the young and adolescents and is often sports-related. The

sudden blow is frequently produced by a baseball, baseball

bat, lacrosse ball, or fist or elbow. The common incidence in

to the flexible ribs and costal cartilages and the thin undevel-

oped chest muscles. Apparently, timing of the blow relative

to the cardiac cycle is critical; ventricular fibrillation is most

wave of the electrical activity of the cardiac muscle.

C L I N I C A L N O T E S

septum to the atrioventricular node. The

Branches

and left ventricle and the atrioventricular septum.

right atrium and right ventricle and parts of the left atrium

lowing branches from the right coronary artery supply the

nary artery in the posterior interventricular groove. The fol

the atrioventricular groove to anastomose with the left coro

the inferior border of the heart it continues posteriorly along

almost vertically in the right atrioventricular groove, and at

pulmonary trunk and the right auricle (Fig. 3.34). It descends

sinus of the ascending aorta and runs forward between the

arises from the anterior aortic

right coronary artery

The

face of the heart, lying within subepicardial connective tissue.

arteries and their major branches are distributed over the sur

immediately above the aortic valve (Fig. 3.41). The coronary

left coronary arteries, which arise from the ascending aorta

The arterial supply of the heart is provided by the right and

valve of the inferior vena cava to the atrioventricular node.

node and descends through the crista terminalis and the

leaves the posterior part of the sinuatrial

nodal pathway

posterior inter-

The Arterial Supply of the Heart

-
-

The

ventricle.

and the upper part of the anterior wall of the right

pulmonary conus (infundibulum of the right ventricle)

supplies the anterior surface of the

right conus artery

conduction.

ordinary atrial myocardial fibers that are responsible for the more rapid

some researchers, who claim that it is the packaging and arrangement of

*The occurrence of specialized internodal pathways has been dismissed by

Basic Anatomy

right

coronary

artery

left coronary artery

circumflex branch

anterior
interventricular
branch

posterior interventricular branch

marginal branch

great cardiac
vein

middle
cardiac
vein

coronary sinus

small cardiac vein

cardiac

vein

FIGURE 3.41

Coronary arteries and veins.

The

the lower margin of the costal surface to reach the apex.

is the largest and runs along

marginal branch

tricle. The

number and supply the anterior surface of the right ven

are two or three in

anterior ventricular branches

The

right ventricle.

number and supply the diaphragmatic surface of the

are usually two in

posterior ventricular branches

The

is replaced by a branch from the left coronary artery.

In 10% of individuals, the posterior interventricular artery

atrioventricular node.

A large septal branch supplies the

rior interventricular branch of the left coronary artery.

the apical part, which receives its supply from the ante

the posterior part of the ventricular septum but not to

cles, including its inferior wall. It supplies branches to

groove. It gives off branches to the right and left ventri

runs toward the apex in the posterior interventricular

posterior interventricular (descending) artery

The

Branches

rior interventricular branch and a circumflex branch.

enters the atrioventricular groove and divides into an ante

the pulmonary trunk and the left auricle (Fig. 3.34). It then

tic sinus of the ascending aorta and passes forward between

and ventricular septum. It arises from the left posterior aor

including the greater part of the left atrium, left ventricle,

right coronary artery, supplies the major part of the heart,

which is usually larger than the

left coronary artery,

The

coronary artery.

and left atria; in 35% of individuals it arises from the left

supplies the node and the right

of the sinuatrial node

artery

terior surface of both the right and left atria. The

faces of the right atrium. One branch supplies the pos

supply the anterior and lateral sur

atrial branches

-
-

The

supplies the pulmonary conus.

left conus artery

A small

arise directly from the trunk of the left coronary artery.

may

(left diagonal artery)

of these ventricular branches

supply the anterior part of the ventricular septum. One

and left ventricles with numerous branches that also

The anterior interventricular branch supplies the right

one third of individuals, it ends at the apex of the heart.

the terminal branches of the right coronary artery. In

posterior interventricular groove and anastomoses with

it then passes around the apex of the heart to enter the

to the apex of the heart (Fig. 3.41). In most individuals,

runs downward in the anterior interventricular groove

anterior interventricular (descending) branch

The

(except for the small area to the right of the anterior inter

supplies all of the right ventricle

right coronary artery

The

Heart in Most Individuals

Summary of the Overall Arterial Supply to the

sustain the muscle.

although sometimes the collateral circulation is enough to

ally leads to myocardial death (myocardial infarction),

one of the larger branches of either coronary artery usu

branches become blocked by disease. A sudden block of

blood supply to the cardiac muscle should one of the large

to provide an adequate

not large enough

they are usually

and left coronary arteries (collateral circulation) exist, but

Anastomoses between the terminal branches of the right

Coronary Artery Anastomoses

left coronary artery (10%).

tricular artery is a branch of the circumflex branch of the

the posterior interven

left dominance,

viduals (90%). In

coronary artery. Right dominance is present in most indi

terior interventricular artery is a large branch of the right

the pos

right dominance,

artery are variable (Fig. 3.42). In

gin, size, and distribution of the posterior interventricular

the diaphragmatic surface of both ventricles. Here the ori

the most common variations affect the blood supply to

Variations in the blood supply to the heart do occur, and

Variations in the Coronary Arteries

supply the left atrium.

Atrial branches

the left ventricle.

supply

posterior ventricular branches

and

ventricular

Anterior

margin of the left ventricle down to the apex.

is a large branch that supplies the left

marginal artery

left

margin of the heart in the atrioventricular groove. A

terventricular artery (Fig. 3.41). It winds around the left

is the same size as the anteriorin

circumflex artery

-
-

ventricular groove), the variable part of the diaphragmatic

CHAPTER 3

The Thorax: Part II—The Thoracic Cavity

circumflex

branch of

left coronary

artery

branches of posterior

interventricular artery

sinuatrial

node

right coronary artery

interventricular

artery

atrioventricular bundle

atrioventricular node

left coronary artery

branches of posterior

interventricular artery

right

coronary

artery

circumflex branch

of left coronary

artery

right

coronary

artery

FIGURE 3.42

(Fig. 3.42).

LBB is supplied by the right and left coronary arteries

ular bundle is supplied by the left coronary artery; the

the right coronary artery. The RBB of the atrioventric

lar node and the atrioventricular bundle are supplied by

sometimes by the left coronary artery. The atrioventricu

The sinuatrial node is usually supplied by the right but

Arterial Supply to the Conducting System

LBB.

tricular septum, most of the left atrium, the RBB, and the

interventricular groove, the anterior two thirds of the ven

tricle, a small area of the right ventricle to the right of the

supplies most of the left ven

left coronary artery

The

node and bundle. The LBB also receives small branches.

atrium, and the sinuatrial node and the atrioventricular

ventricular septum, the right atrium and part of the left

surface of the left ventricle, the posteroinferior third of the

Anterior view of the heart showing the relationship of the blood supply to the conducting system.

the left dominance.

Posterior view of the heart showing the origin and distribution of the posterior interventricular artery in

Posterior view of the heart showing the origin and distribution of the posterior interventricular artery in the

right dominance. B.

Coronary Artery Disease

blockage are caused by an acute thrombosis on top of a chronic

The myocardium receives its blood supply through the right

and left coronary arteries. Although the coronary arteries have

numerous anastomoses at the arteriolar level, they are essen-

tially functional end arteries. A sudden block of one of the large

branches of either coronary artery will usually lead to necrosis

of the cardiac muscle (myocardial infarction) in that vascular

area, and often the patient dies. Most cases of coronary artery

atherosclerotic narrowing of the lumen.

C L I N I C A L N O T E S

(continued)

Basic Anatomy

Arteriosclerotic disease of the coronary arteries may pres

that have been carried out before treatment. For this reason, a

coronary artery stenting are now commonly accepted methods

Because coronary bypass surgery, coronary angioplasty, and

infarction, the artery involved, and the electrocardiographic

be helpful when attempting to correlate the site of myocardial

the different areas of the myocardium. This information can

Table 3.1 shows the different coronary arteries that supply

occurs when coronary flow is suddenly

Myocardial infarction

that myocardial ischemia occurs on exertion but not at rest. (3)

rest. In this condition, the coronary arteries are so narrowed

is cardiac pain that occurs on exertion and is relieved by

the myocardium occur over many years and are caused by a

lumina of the arteries: (1) General degeneration and fibrosis of

ent in three ways, depending on the rate of narrowing of the

gradual narrowing of the coronary arteries. (2) Angina pecto-
ris

reduced or stopped and the cardiac muscle undergoes necro-

sis. Myocardial infarction is the major cause of death in indus-

trialized nations.

signature.

of treating coronary artery disease, it is incumbent on the student

to be prepared to interpret still- and motion-picture angiograms

working knowledge of the origin, course, and distribution of the

coronary arteries should be memorized.

Coronary Artery

Infarct Location

ECG Signature

Proximal LAD

Large anterior wall

ST elevation: I, L, V1–V6

More distal LAD

Anteroapical

Inferior wall if wraparound LAD

ST elevation: V2–V4

ST elevation: II, III, F

Distal LAD

Anteroseptal

ST elevation: V1–V3

Early obtuse, marginal

High lateral wall

ST elevation: I, L, V4–V6

More distal marginal branch, circumflex

Small lateral wall

ST elevation: I, L, or V4–V6, or no abnormality

ECG, electrocardiographic; LAD, left anterior descending (interventricular); RCA, right coronary artery.

Circumflex

Posterolateral

ST elevation: V4–V6; ST depression: V1–V2

Distal RCA

Small inferior wall

ST elevation: II, III, F; ST depression: I, L

Proximal RCA

Large inferior wall and posterior wall

Some lateral wall

ST elevation: II, III, F; ST depression: I, L, V1–V3

ST elevation: V5–V6

RCA

Right ventricular

Usually inferior

ST elevation: V2R–V4R; some ST elevation: V1;

or ST depression V2, V3

ST elevation: II, III, F

Coronary Artery Lesions, Infarct Location, and ECG Signature

T A B L E 3 . 1

reflexes.

ning with the vagus nerves take part in cardiovascular

consciousness via this pathway. Afferent fibers run

myocardium become impaired, pain impulses reach

sciousness. However, should the blood supply to the

carry nervous impulses that normally do not reach con

Afferent fibers running with the sympathetic nerves

arteries.

traction of the heart and a constriction of the coronary

nerves results in a reduction in the rate and force of con

coronary arteries. Activation of the parasympathetic

on the sinuatrial and atrioventricular nodes and on the

The postganglionic parasympathetic fibers terminate

coronary arteries.

contraction of the cardiac muscle, and dilatation of the

nerves results in cardiac acceleration, increased force of

fibers, and on the coronary arteries. Activation of these

sinuatrial and atrioventricular nodes, on cardiac muscle

The postganglionic sympathetic fibers terminate on the

pathetic supply comes from the vagus nerves.

racic portions of the sympathetic trunks, and the parasym

sympathetic supply arises from the cervical and upper tho

situated below the arch of the aorta. The

thetic fibers of the autonomic nervous system via the

The heart is innervated by sympathetic and parasympa

that open directly into the heart chambers.

(Fig. 3.41) and by small veins

anterior cardiac vein

by the

The remainder of the blood is returned to the right atrium

are tributaries of the coronary sinus.

middle cardiac veins

small

atrium to the left of the inferior vena cava. The

It opens into the right

great cardiac vein.

tinuation of the

posterior part of the atrioventricular groove and is a con

through the coronary sinus (Fig. 3.41), which lies in the

Most blood from the heart wall drains into the right atrium

Venous Drainage of the Heart

and

Nerve Supply of the Heart

car-

diac plexuses

-
-

CHAPTER 3

The Thorax: Part II—The Thoracic Cavity

Cardiac Pain

matic surface of the heart often gives rise to discomfort in the

costobrachial nerve communicates with the medial cutaneous

areas supplied by the upper four intercostal nerves and by the

Pain originating in the heart as the result of acute myocardial

ischemia is assumed to be caused by oxygen deficiency and the

accumulation of metabolites, which stimulate the sensory nerve

endings in the myocardium. The afferent nerve fibers ascend to

the central nervous system through the cardiac branches of the

sympathetic trunk and enter the spinal cord through the poste-

rior roots of the upper four thoracic nerves. The nature of the

pain varies considerably, from a severe crushing pain to nothing

more than a mild discomfort.

The pain is not felt in the heart, but is referred to the skin

areas supplied by the corresponding spinal nerves. The skin

intercostobrachial nerve (T2) are therefore affected. The inter-

nerve of the arm and is distributed to skin on the medial side of

the upper part of the arm. A certain amount of spread of nervous

information must occur within the central nervous system, for

the pain is sometimes felt in the neck and the jaw.

Myocardial infarction involving the inferior wall or diaphrag-

epigastrium. One must assume that the afferent pain fibers from

the heart ascend in the sympathetic nerves and enter the spinal

cord in the posterior roots of the seventh, eighth, and ninth tho-

racic spinal nerves and give rise to referred pain in the T7, T8,

and T9 thoracic dermatomes in the epigastrium.

Because the heart and the thoracic part of the esophagus

probably have similar afferent pain pathways, it is not surprising

that painful acute esophagitis can mimic the pain of myocardial

infarction.

C L I N I C A L N O T E S

Action of the Heart

opposite the 3rd intercostal space.

lies behind the left half of the sternum

aortic valve

The

sternum.

third left costal cartilage and the adjoining part of the

lies behind the medial end of the

pulmonary valve

The

opposite the 4th costal cartilage.

lies behind the left half of the sternum

mitral valve

The

num opposite the 4th intercostal space.

lies behind the right half of the ster

tricuspid valve

The

(Fig. 3.14):

56. The surface markings of the heart valves are as follows

The surface projection of the heart was described on page

Surface Anatomy of the Heart Valves

aortic and pulmonary orifices.

The cusps float into apposition and completely close the

and immediately fills the pockets of the semilunar valves.

systole, blood begins to move back toward the ventricles

is ejected from the heart. At the conclusion of ventricular

the semilunar valve cusps are pushed aside, and the blood

present in the large arteries (aorta and pulmonary trunk),

Once the intraventricular blood pressure exceeds that

the same time throughout the ventricles.

fibers, ensures that myocardial contraction occurs at almost

(Fig. 3.38) and its terminal branches, including the Purkinje

of the cardiac impulse along the atrioventricular bundle

tracting and the atrioventricular valves close. The spread

chordae tendineae. Meanwhile, the ventricles start con

muscles then begin to contract and take up the slack of the

tricular bundle and its branches (Fig. 3.38). The papillary

node, is conducted to the papillary muscles by the atrioven

The cardiac impulse, having reached the atrioventricular

this means, blood does not reflux into the veins.

large veins and milks the blood toward the ventricles. By

in the atria, which commences around the openings of the

tricles. The sinuatrial node initiates the wave of contraction

forces the remainder of the blood in the atria into the ven

When the ventricles are nearly full, atrial systole occurs and

passively flows from the atria to the ventricles (Fig. 3.38).

ation) occurs, the atrioventricular valves open, and blood

in the large veins and atria. Once ventricular diastole (relax

valves are closed, the blood is temporarily accommodated

ventricular systole (contraction), when the atrioventricular

Blood is continuously returning to the heart; during

150 times per minute in the newborn child.

70 to 90 times per minute in the resting adult and 130 to

The normal heart beats

cardiac cycle.

referred to as the

take place within it as it fills with blood and empties is

The heart is a muscular pump. The series of changes that

■

Auscultation of the Heart Valves

produced at each valve with the minimum of distraction or

the chest wall so that he or she will be able to hear sounds

for a physician to know where to place the stethoscope on

closure of the aortic and pulmonary valves. It is important

and mitral valves. The second sound is produced by the sharp

contraction of the ventricles and the closure of the tricuspid

The first sound is produced by the

lu¯b-du˘p.

two sounds:

On listening to the heart with a stethoscope, one can hear

interference.

C L I N I C A L N O T E S

(continued)