CHAPTER 2: THORAX PART II: HEART Flashcards
1
Q
What is Pericardium?
A
The pericardium is a fibroserous sac that encloses the
heart and the roots of the great vessels.
2
Q
What is the function of pericardium?
A
Its function is to
restrict excessive movements of the heart as a whole and to serve as a lubricated container in which the different parts of the heart can contract.
3
Q
Where does the pericardium lies?
A
The pericardium lies within the
middle mediastinum(Figs. 3.2, 3.30, 3.31, and 3.32),posterior to the body of the sternum and the 2nd to the 6th costal cartilagesandanterior to the 5th to the 8th thoracic vertebrae.
4
Q
What are the types of Pericardium?
A
- Fibrous Pericardium
- Serous Pericardium
5
Q
What is the fibrous pericardium?
A
The fibrous pericardium is the strong fibrous part of the
sac.
It is firmly attached below to the central tendon of the
diaphragm.
It fuses with the outer coats of the great blood
vessels passing through it (Fig. 3.31)—namely, the aorta, the pulmonary trunk, the superior and inferior venae cavae, and the pulmonary veins (Fig. 3.32).
The fibrous pericardium is attached in front to the sternum by the sternopericardial
ligaments.
6
Q
What is serous pericardium?
A
The serous pericardium lines the fibrous pericardium and
coats the heart.
It is divided into parietal and visceral layers
(Fig. 3.31).
The parietal layer lines the fibrous pericardium and is
reflected around the roots of the great vessels to become
continuous with the visceral layer of serous pericardium
that closely covers the heart (Fig. 3.32).
7
Q
What is serious pericardium?
A
It is divided into parietal and visceral layers
(Fig. 3.31).
The parietal layer lines the fibrous pericardium and is
reflected around the roots of the great vessels to become
continuous with the visceral layer of serous pericardium
that closely covers the heart (Fig. 3.32).
8
Q
What does the parietal layer line?
A
The parietal layer lines the fibrous pericardium and is
reflected around the roots of the great vessels to become continuous with the visceral layer of serous pericardium that closely covers the heart (Fig. 3.32).
9
Q
What is the visceral layer of the pericardium?
A
The visceral layer is closely applied to the heart and is
often called the epicardium.
The slitlike space between the
parietal and visceral layers is referred to as the pericardial
cavity (Fig. 3.31).
10
Q
What is the normal amount of pericardial fluid?
A
Normally, the cavity contains a small
amount of tissue fluid (about 50 mL),the pericardial fluid, whichacts as a lubricant to facilitate movements of the heart.
11
Q
What is the oblique sinus?
A
On the posterior surface of the heart, the reflection of the serous pericardium around the large veins forms a recess called the oblique sinus (Fig. 3.32).
12
Q
What is the transverse sinus
A
Also on the posterior surface of the heart is the transverse sinus, which is a short passage
that lies between the reflection of serous pericardium around the aorta and pulmonary trunk and the reflection around the large veins (Fig. 3.32).
The pericardial sinuses form as a consequence
of the way the heart bends during development (see
page 91). They have no clinical significance.
13
Q
How is the pericardial sinus formed?
A
The pericardial sinuses form as a consequence
of the way the heart bends during development (see
page 91).
They have no clinical significance.
14
Q
Nerve Supply of the Pericardium
What nerve supplies the fibrous pericardium and the parietal layer of the serous pericardium?
A
The fibrous pericardium and the parietal layer of the serous pericardium are supplied by the phrenic nerves.
15
Q
The visceral layer of the serous pericardium is innervated by?
A
The visceral layer of the serous pericardium is innervated by
branches of the sympathetic trunks and the vagus nerves.
16
Q
Desrcibe the Heart.
A
The heart is a hollow muscular organ that is somewhat pyramid
shapedandlies within the pericardium in the mediastinum
(Figs. 3.33 and 3.34).
It is connected at its base to
the great blood vessels but otherwise lies free within the pericardium.
17
Q
Surfaces of the Heart
A
The heart has three surfaces:
- sternocostal (anterior),
- diaphragmatic (inferior), and a
- base (posterior).
It also has an apex, which is directed downward, forward, and to the left.
18
Q
What is pericarditis?
A
In inflammation of the serous pericardium, called pericarditis, pericardial fluid may accumulate excessively, which can compress
- *the thin-walled atria and interfere with the filling of the**
- *heart during diastole.**
This compression of the heart is called
cardiac tamponade.
19
Q
What is cardiac tamponade?
A
This compression of the heart is called
cardiac tamponade.
Cardiac tamponade can also occur secondary to stab or gunshot wounds when the chambers of the heart have been penetrated.
The blood escapes into the pericardial cavity and can
restrict the filling of the heart.
20
Q
What is pericardial friction rub?
A
Roughening of the visceral and parietal layers of serous pericardium
by inflammatory exudate in acute pericarditis produces
pericardial friction rub, which can be felt on palpation and heard through a stethoscope.
21
Q
What is paracentesis?
A
Pericardial fluid can be aspirated from the pericardial cavity should excessive amounts accumulate in pericarditis.
This process
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.
22
Q
What forms the sternocostal surface ?
A
The sternocostal surface is formed mainly by the
right atrium and the right ventricle,which areseparated from each other by the vertical atrioventricular groove
(Fig. 3.34).
- right border is formed by the right atrium;
- left border, by the left ventricle and part of the left auricle.
The right ventricle is separated from the left ventricle
by the anterior interventricular groove.
23
Q
The anterior interventricular groove separates what?
A
The right ventricle is separated from the left ventricle
by the anterior interventricular groove.
24
Q
What forms the diaphragmatic surface of the heart?
A
The diaphragmatic surface of the heart is formed
mainly by the right and left ventricles separated by the posterior interventricular groove.
The inferior surface of the right atrium, into which the inferior vena cava opens, also
forms part of this surface.
25
What forms the base or posterior surface of the heart?
The **base of the heart, or the posterior surface**, is formed
mainly by the left atrium, into which open the four pulmonary
veins (Fig. 3.35).
The base of the heart lies opposite the apex.
26
What forms the apex of the heart?
The **apex of the heart**, formed by the **left ventricle,** is
directed downward, forward, and to the left (Fig. 3.34).
It lies at the **level of the fifth left intercostal space, 3.5 in.**
(9 cm) from the midline.
In the region of the apex, the apex
beat can usually be seen and palpated in the living patient.
**Note that the base of the heart is called the base because the heart is pyramid shaped; the base lies opposite the apex.
The heart does not rest on its base; it rests on its diaphragmatic
(inferior) surface.**
27
Why is the base of the heart called as such?
Note that the base of the heart is called the base **because the heart is pyramid shaped;** the base **lies opposite the apex.**
* *The heart does not rest on its base; it rests on its diaphragmatic
(inferior) surface.**
28
The heart rest s on its base.
T or F
FALSE
The **heart does not rest on its base;** it rests on its diaphragmatic
(inferior) surface.
29
What are the Borders of the Heart?
Borders of the Heart
* right border: **right atrium**
* left border: **left auricle**
* below:**left ventricle**
(Fig. 3.34).
* The **lower border** is **formed mainly by the right**
**ventricle** but also by the **right atrium;**
* the apex is formed bythe left ventricle.
**These borders are important to recognize when examining a radiograph of the heart.**
30
Chambers of the Heart
* Right Atrium
* Right Ventricle
* Left Atrium
* Left Ventricle
31
What divides the heart into four chambers?
The heart is divided by **vertical septa** into **four chambers:** the r**ight and left atria and the right and left ventricles.**
The **right atrium lies anterior** to the **left atrium**, and the **right ventricle lies anterior to the left ventricle.**
32
What composes the walls of the heart?
The walls of the heart are composed of:
* **cardiac muscle**, :**the myocardium**;
* **epicardium:**covered externally with serous pericardium
* **endocardium:** and **lined internally with a layer of endothelium**
33
What consist right atrium?
The right atrium consists of a **main cavity and a small outpouching,** the auricle (Figs. 3.34 and 3.36).
34
What can you find on the outside of the right atrium?
On the outside
* **vertical groove**,
* the **sulcus terminalis**
* **crista terminalis.**
35
What is the main part of the atrium that lies posterior to the ridge?
The **main part of the atrium** that lies posterior to the ridge is **smooth walled** and is **derived embryologically from the sinus venosus.**
36
Describe the front of the atrium.
The part of the atrium in **front of the ridge is roughened or trabeculated by bundles of muscle fibers**, the **musculi pectinati**, which run from the crista terminalis to the auricle.
37
Where does the anterior part of the right atrium derived?
This anterior part is derived embryologically
from the **primitive atrium.**
38
What is sulcus terminalis?
On the outside
of the heart at the **junction between the right atrium and the right auricle** is a vertical groove, the sulcus terminalis,
39
What is the auricle?
The **right atrium** consists of a **main cavity and a small outpouching, the auricle** (Figs. 3.34 and 3.36).
40
What is crista terminalis?
On the outside
of the heart at the junction between the right atrium and the right auricle is a vertical groove, the sulcus terminalis, **which on the inside forms a ridge, the crista terminalis.**
41
Where does the main part of the atrium that lies posteriogir to the ridge embryologically derived?
The main part of the atrium that lies posterior to the ridge
is smooth walled and is derived **embryologically from the
*sinus venosus****.*
42
What is musculi pectinati?
The part of the atrium in front of the ridge
is **roughened or trabeculated by bundles of muscle fibers, the musculi pectinati,** which run from the crista terminalis
to the auricle.
This anterior part is derived embryologically
from the primitive atrium
43
Openings into the Right Atrium
* superior vena cava
* inferior vena cava
* coronary sinus
* right atrioventricular orifice
44
Where does the superior vena cava opens?
The superior vena cava (Fig. 3.36) **opens into the upper
part of the right atrium**;**it has no valve.**
It **returns the blood
to the heart from the upper half of the body.**
45
The superior vena cava has a valve?
T or F
FALSE
The superior vena cava (Fig. 3.36) opens into the upper
part of the right atrium; it has no valve.
It returns the blood
to the heart from the upper half of the body.
46
Where does the inferior vena cava opens?
```
The inferior
vena cava (larger than the superior vena cava) **opens into
the lower part of the right atrium**; it is**guarded by a rudimentary, nonfunctioning valve**.
```
It returns the blood to the
heart from the lower half of the body
47
What is the coronary sinus?
The coronary sinus, which **drains most of the blood
*from* the heart wall**(Fig. 3.36),**opens into the right atrium**between the**inferior vena cava and the atrioventricular orifice.**
It is **guarded by a rudimentary, nonfunctioning valve.**
48
What is the right atrioventricular orifice?
The right atrioventricular orifice **lies anterior to the
inferior vena caval opening**and is**guarded by the tricuspid valve** (Fig. 3.36).
Many small orifices of small veins also drain the wall of
the heart and open directly into the right atrium.
49
Fetal Remnants in the R atrium.
* foramen ovale
50
In addition to the rudimentary valve of the inferior vena
cava are the ___ and \_\_\_.
In addition to the rudimentary valve of the inferior vena
cava are the fossa ovalis and anulus ovalis.
51
What is anulus ovalis?
anulus ovalis.
These latter
structures **lie on the atrial septum**, which **separates the
right atrium from the left atrium**(Fig. 3.36).
52
What is fossa ovalis?
The fossa ovalis
is a **shallow depression**, which is the **site of the foramen ovale in the fetus** (Fig. 3.37).
53
What forms the anulus ovalis?
The anulus ovalis forms the
**upper margin of the fossa.**
54
What represents the floor of the fossa ovalis?
The floor of the fossa represents
the **persistent septum primum** of the heart of the embryo.
55
What forms the anulus ovalis?
and the anulus is formed from the lower edge of the septum secundum (Fig. 3.37).
56
What is fossa ovalis?
The fossa ovalis
is a shallow depression, which is the **site of the foramen ovale in the fetus** (Fig. 3.37).
57
What is the infundibulum?
The right ventricle communicates with the right atrium
through the **atrioventricular orifice** and with the **pulmonary trunk through the pulmonary orifice** (see Fig. 3.36).
As the cavity approaches the pulmonary orifice, it becomes funnel shaped, at which point it is referred to as the **infundibulum.**
58
Describe the right atrium.
The **walls of the right ventricle** are **much thicker than
those of the right atrium**and**show several internal projecting ridges formed of muscle bundles**.
The projecting ridges give
the **ventricular wall a spongelike appearance and are known
as trabeculae carneae.**
59
What is the trabeculae carneae?
The walls of the right ventricle are much thicker than
those of the right atrium and show several internal projecting ridges formed of muscle bundles.
The **projecting ridges give
the ventricular wall a spongelike appearance and are known as trabeculae carneae.**
60
What are the three types of trabeculae carnae?
The trabeculae carneae are composed
of three types.
* The **first type comprises the papillary muscles,** which project inward, being attached by their bases to the ventricular wall; their apices are connected by fibrous chords (the chordae tendineae) to the cusps of the tricuspid valve (Fig. 3.36).
* The **second type is attached at the ends to the ventricular wall**, being free in the middle. One of these, the moderator band, crosses the ventricular cavity from the septal to the anterior wall. It conveys the right branch of the atrioventricular bundle, which is part of the conducting system of the heart.
* The third type is simply composed of **prominent ridges.**
61
What is the function tricuspid valve?
The tricuspid valve **guards the atrioventricular orifice**
(Figs. 3.36 and 3.38) and **consists of three cusps formed by a**
**fold of endocardium with some connective tissue** enclosed:
anterior, septal, and inferior (posterior) cusps.
62
The tricuspid valve guards the atrioventricular orifice
(Figs. 3.36 and 3.38) and consists of three cusps formed by a
fold of endocardium with some connective tissue enclosed:
* anterior,
* septal, and
* inferior (posterior) cusps.
63
Where does the anterior cusp of the tricuspid valve lies?
The anterior
cusp lies anteriorly.
64
Where does the septal cusp of the tricuspid valve lies?
the septal cusp lies against the
ventricular septum
65
Where does the inferior or posterior cusp lies?
and the inferior or posterior cusp lies inferiorly.
66
What is chordae tendinae?
The tricuspid cusp free edges and ventricular surfaces **are attached to the chordae**
**tendineae.**
67
What happens when the Right ventricle contracts?
The chordae tendineae connect the cusps
to the papillary muscles.
When the ventricle contracts,
the **papillary muscles contract and prevent the cusps from being forced into the atrium and turning inside out as the intraventricular pressure rises.**
To assist in this process, the
chordae tendineae of one papillary muscle are connected to the adjacent parts of two cusps.
68
Describe the pulmonary valve.
The pulmonary valve guards the pulmonary orifice
(Fig. 3.38A) and consists of three semilunar cusps formed by folds of endocardium with some connective tissue enclosed. The curved lower margins and sides of each cusp
are attached to the arterial wall.
The open mouths of the
cusps are directed upward into the pulmonary trunk.
No
chordae or papillary muscles are associated with these valve cusps; the attachments of the sides of the cusps to the arterial wall prevent the cusps from prolapsing into the ventricle.
69
What is the arrangement of the semilunar cusp?
The three semilunar cusps are arranged with :
* one posterior (left cusp) and
* two anterior (anterior and right cusps).
(The cusps of the pulmonary and aortic valves are named according to their position in the fetus before the heart has rotated to the left.
This, unfortunately, causes a great deal
of unnecessary confusion.)
During ventricular systole, the
cusps of the valve are pressed against the wall of the pulmonary trunk by the outrushing blood.
During diastole, blood flows back toward the heart and enters the sinuses; the valve cusps fill, come into apposition in the center of the lumen, and close the pulmonary orifice.
70
Describe the left atrium.
Similar to the right atrium, the left atrium consists of a
**main cavity and a left auricle.**
The left atrium is situated
**behind the right atrium** and **forms the greater part of the base or the posterior surface of the heart** (see Fig. 3.35).
71
What lies behind the left atrium?
Behind it lies the **oblique sinus of the serous pericardium**, and the fibrous pericardium separates it from the esophagus
(Figs. 3.32 and 3.39)
72
What separates oblique sinus of the serous pericardium,
from the esophagus
fibrous pericardium separates it from the esophagus
| (Figs. 3.32 and 3.39)
73
Describe the interior of the left atrium.
The interior of the left atrium is smooth, but the left
auricle possesses muscular ridges as in the right auricle.
74
Openings into the Left Atrium
The four pulmonary veins, two from each lung, open
through the posterior wall (Fig. 3.35) and **have no valves**.
The left atrioventricular orifice is guarded by the **mitral valve.**
75
How does the left ventricle communicates with the atrioventricular orifice and with the aorta?
The left ventricle communicates with the left atrium
through the **atrioventricular orifice** and with the **aorta
through the aortic orifice.**
76
Describes the walls of the left ventricle.
The walls of the left ventricle
(Fig. 3.38) are three times thicker than those of the right ventricle.
**(The left intraventricular blood pressure is six
times higher than that inside the right ventricle.)**
In cross section, the **left ventricle is circular;** the right is **crescentic because of the bulging of the ventricular septum** into the cavity of the right ventricle (Fig. 3.38).
There are **welldeveloped
trabeculae carneae, two large papillary muscles,**
but no moderator band.
The part of the ventricle below the
aortic orifice is called the **aortic vestibule**.
77
Describe the mitral valve.
The mitral valve guards the atrioventricular orifice
(Fig. 3.38).
It consists of **two cusps,** one anterior and one
posterior, which have a structure similar to that of the cusps of the tricuspid valve.
The anterior cusp is the larger and
intervenes between the atrioventricular and aortic orifices.
The attachment of the chordae tendineae to the cusps and the papillary muscles is similar to that of the tricuspid valve.
78
Describes the aortic valve
The aortic valve guards the aortic orifice and is precisely similar in structure to the pulmonary valve (Fig. 3.38).
One cusp is situated on the anterior wall (right cusp) and two are located on the posterior wall (left and posterior cusps).
**Behind each cusp, the aortic wall bulges to form an aortic sinus.**
79
What does the anterior aortic sinus gives origin to what?
The anterior aortic sinus gives origin to the right
**coronary artery,** and the **left posterior sinus gives origin to the left coronary artery.**
80
Describe the Structure of the Heart.
The walls of the heart are composed of a thick layer of cardiac muscle, the myocardium, covered externally by the epicardium and lined internally by the endocardium.
The **atrial portion of the heart** has relatively thin walls and is divided by the atrial (interatrial) septum into the right and left atria. The septum runs from the anterior wall of the heart backward and to the right.
The **ventricular** portion of
the heart has thick walls and is divided by the ventricular (interventricular) septum into the right and left ventricles.
The septum is placed obliquely, with one surface facing forward and to the right and the other facing backward and to the left. Its position is indicated on the surface of the heart by the anterior and posterior interventricular grooves.
The
lower part of the septum is thick and formed of muscle.
The smaller upper part of the septum is thin and membranous and attached to the fibrous skeleton.
81
What consist the so-called skeleton of the heart?
The so-called skeleton of the heart (Fig. 3.38) consists
of **fibrous rings that surround the atrioventricular,**
**pulmonary, and aortic orifices** and are **continuous with
the membranous upper part of the ventricular septum**.
The
fibrous rings around the atrioventricular orifices separate the muscular walls of the atria from those of the ventricles
but provide attachment for the muscle fibers.
The fibrous
rings support the bases of the valve cusps and prevent the valves from stretching and becoming incompetent.
***The
skeleton of the heart forms the basis of electrical discontinuity between the atria and the ventricles.***
82
What is the normal HR of resting adult?
The normal heart contracts rhythmically at about 70 to 90 beats per minute in the resting adult.
83
Describe the contractile system of the heart.
The rhythmic contractile
process originates spontaneously in the conducting
system and the impulse travels to different regions of the heart, so the atria contract first and together, to be followed later by the contractions of both ventricles together.
The
slight delay in the passage of the impulse from the atria to the ventricles allows time for the atria to empty their blood into the ventricles before the ventricles contract
84
What is the reason for the slight delay in the passage of impulse from the atria to the ventricles?
The
slight delay in the passage of the impulse from the atria to the ventricles **allows time for the atria to empty their blood into the ventricles before the ventricles contract**
85
The conducting system of the heart consists of specialized cardiac muscle present in the:
The conducting system of the heart consists of specialized cardiac muscle present in the:
* **sinuatrial node,**
* **atrioventricular node**
* **atrioventricular bundle** and its right and left terminal branches, and the
* **subendocardial plexus of Purkinje fibers** (specialized cardiac muscle fibers that form the conducting system of the heart).
86
Where is the SA node located?
The sinuatrial node is located in the wall of the right atrium in the upper part of the sulcus terminalis just to the right of the opening of the superior vena cava (Figs. 3.36 and3.40).
87
Describe the sinuatrial node.
The node spontaneously gives origin to rhythmic electrical impulses that spread in all directions through the cardiac muscle of the atria and cause the muscle to contract.
88
Where is the AV node located?
The **atrioventricular node** is strategically placed on the
**lower part of the atrial septum just above the attachment of the septal cusp of the tricuspid valve** (Figs. 3.37 and 3.38).
89
Describe the AV node.
From it, the cardiac impulse is conducted to the ventricles
by the atrioventricular bundle.
The atrioventricular node is
stimulated by the excitation wave as it passes through the
atrial myocardium.
90
What is the speed of conduction of the AV node?
The speed of conduction of the cardiac impulse through
the atrioventricular node (about 0.11 seconds) allows sufficient time for the atria to empty their blood into the ventricles before the ventricles start to contract.
91
Describe the atrioventricular bundle (bundle of His).
The atrioventricular bundle (bundle of His) is the **only
pathway of cardiac muscle that connects the myocardium
of the atria and the myocardium of the ventricles and is
thus the only route along which the cardiac impulse can
travel from the atria to the ventricle**s (Fig. 3.40). The bundle descends through the fibrous skeleton of the heart
The atrioventricular bundle then descends behind the
septal cusp of the tricuspid valve to reach the inferior
border of the membranous part of the ventricular septum.
At the upper border of the muscular part of the septum, it divides into two branches, one for each ventricle.
The right bundle branch (RBB) passes down on the right side of the ventricular septum to reach the moderator band, where it crosses to the anterior wall of the right ventricle.
Here, it becomes continuous with the fibers of the Purkinje plexus (Fig. 3.40).
The left bundle branch (LBB) pierces the septum and
passes down on its left side beneath the endocardium. It
usually divides into two branches (anterior and posterior),
which eventually become continuous with the fibers of the
Purkinje plexus of the left ventricle.
It is thus seen that the conducting system of the heart
is responsible not only for generating rhythmic cardiac
impulses, but also for conducting these impulses rapidly throughout the myocardium of the heart so that the different chambers contract in a coordinated and efficient manner.
The activities of the conducting system can be influenced by the autonomic nerve supply to the heart. The parasympathetic nerves slow the rhythm and diminish the rate of conduction of the impulse; the sympathetic nerves
have the opposite effect.
92
Internodal Conduction Paths\*
Impulses from the sinuatrial node have been shown to
travel to the atrioventricular node more rapidly than they can travel by passing along the ordinary myocardium.
This
phenomenon has been explained by the description of
special pathways in the atrial wall (Fig. 3.40), which have a structure consisting of a mixture of Purkinje fibers and ordinary cardiac muscle cells.
The **anterior internodal**
pathway leaves the anterior end of the sinuatrial node
and passes anterior to the superior vena caval opening.
It
descends on the atrial septum and ends in the atrioventricular node.
The **middle internodal pathway** leaves the
posterior end of the sinuatrial node and passes posterior to
the superior vena caval opening. It descends on the atrial septum to the atrioventricular node.
The **posterior internoda**l pathway leaves the posterior part of the sinuatrial
node and descends through the crista terminalis and the
valve of the inferior vena cava to the atrioventricular node.
93
Where does the anterior internodal pathway leaves?
The anterior internodal pathway **leaves the anterior** **end of the sinuatrial node and passes anterior to the superior vena caval opening**.
It **descends on the atrial septum and ends in the atrioventricular node.**
94
Where does the middle internodal pathway leaveS?
The middle internodal pathway **leaves the posterior end of the sinuatrial node and passes posterior to the superior vena caval opening.** It descends on the atrial septum to the atrioventricular node.
95
Where does the posterior pathway leaves?
The posterior internodal pathway **leaves the posterior part of the sinuatrial node and descends through the crista terminalis and the valve of the inferior vena cava to the atrioventricular node**
96
What is the spontaneous source of the cardiac impulse?
The sinuatrial node is the spontaneous source of the cardiac impulse.
97
The _______ is responsible for **picking up the cardiac impulse from the atria**
The atrioventricular node is responsible for picking up the cardiac impulse from the atria.
98
What is the only route by which the cardiac impulse can spread from the atria to the ventricles?
The atrioventricular bundle is the only route by which the cardiac impulse can spread from the atria to the ventricles.
99
Failure of the bundle to conduct the normal impulses results in what?
Failure of the bundle to conduct the normal impulses results in **alteration in the rhythmic contraction of the ventricles (arrhythmias**) or, **if complete 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.**
100
What is 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-relate**d.
The sudden blow is frequently produced by a **baseball, baseball bat, lacrosse ball, or fist or elbow**. The common incidence in the young is **most likely due to the compliant chest wall due to the flexible ribs and costal cartilages and the thin undeveloped chest muscles**.
Apparently, timing of the blow relative to the cardiac cycle is critical; **ventricular fibrillation is most likely to occur if the blow occurs during the upstroke of the T wave of the electrical activity of the cardiac muscle**.
101
Apparently, timing of the blow relative to the cardiac cycle is critical; ventricular fibrillation is most likely to occur if the blow occurs during the\_\_\_\_\_\_\_\_\_\_\_\_\_
upstroke of the T wave of the electrical activity of the cardiac muscle.
102
