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Introduction

Well, you’ve finished all the chapters, you’ve passed each of the chapter tests, and

you’ve practiced, practiced, practiced. Do you think you’re ready to take on the Final

Challenge? Here’s how to test yourself to see how good you really are.

First, set aside about an hour or two of uninterrupted time. This should be closedbook, so all you’ll need is a pencil and your calipers. Tackle each strip in order; don’t

skip around. When you’re done, turn to the answer key to correct yourself. If you

want to score yourself, each strip is worth one percentage point (i.e., if you miss five,

your score is 95%). On a standard scale, a score of 90% or above is an A, 80–89% is a B,

70–79% is a C, 60–69% is a D, and below 60% is failing.

Keep in mind that this isn’t an algebra test, where all the questions have equal

value. Some rhythms are more significant than others, so it’s important for you to

be able to interpret accurately across all the rhythm categories. After you’ve graded

yourself, go back and tally any you missed. Look for clustering or any other pattern

that might suggest a weak area; then use that information to target supplemental study.

Okay. Are you ready? Good luck, and enjoy it.

Final Challenge

10

404 Chapter 10

SELF-TEST (answers can be found in the Answer Key on page 580)

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454

Overview

IN THIS APPENDIX, you will learn about the structure and function of the heart. You will learn

about its chambers, valves, walls, surfaces, and surrounding pericardial sac. You will find out

how the heart contracts in response to electrical stimulation, and you will learn about the stages

of contraction: systole and diastole. You will also learn about the blood vessels that supply the

heart itself: the coronary arteries, cardiac veins, and coronary sinus.

Cardiac Anatomy and

Physiology

Appendix A

The cardiovascular system serves to carry oxygen from the

lungs to tissues throughout the body. In a never-ending

cycle, blood circles throughout the body, taking oxygen from

the lungs to the tissues, then taking carbon dioxide from the

tissues back to the lungs to exchange for new oxygen.

The heart’s role in this process is to keep the blood

circulating. To accomplish this task, it has two separate but

interrelated systems: a mechanical mechanism that actually

pumps the blood and an electrical system that tells the

mechanical system how and when to pump. This appendix

outlines the heart’s mechanical system, while the body of the

book is devoted to cardiac electrical function.

Location and Structure

The heart is a hollow, muscular, cone-shaped organ,

roughly the size of a fist. It is located in the chest, behind the

sternum and between the lungs. Just above it are the great

Cardiac Anatomy and Physiology 455

vessels (aorta and superior vena cava), and below it is the

diaphragm (Figure A1).

The heart sits slightly off center, with 2/3 of its mass

lying to the left of the middle. It’s also tilted slightly. The

upper end (called the base) is pointed upward and to the

right, while the lower point (called the apex) slants downward and to the left. The apex moves toward the anterior

chest wall during contraction, allowing its beats to be felt

just below the left nipple.

Internal Chambers

The heart consists of four hollow chambers: the two upper

chambers are called atria, and the two lower chambers are

the ventricles. The walls of the ventricles are much thicker

than those of the atria, because the lower chambers have to

pump blood much farther than do the atria.

Between the two upper chambers is a thin wall called the

interatrial septum. A thicker, more muscular interventricular

septum sits between the two lower chambers (Figure A2).

Heart Walls

All the walls of the heart consist of three layers (Figure A3):

Endocardium: contains the branches of the heart’s

electrical conduction system

Myocardium: made up of layers and bands of cardiac

muscle fibers that are wound in complex spirals

around the atria and ventricles

Figure A1 Location of the Heart

Apex

Sternum Clavicle

Diaphragm

Base

Figure A2 Internal Anatomy of the Heart

Right Ventricle

Left Ventricle

Left Atrium

Pulmonary Veins

Interatrial Septum Right Atrium

Interventricular

Septum

Aorta Pulmonary Arteries

Superior

Vena Cava

Inferior

Vena Cava

456 Appendix A

Epicardium: single layer of cells supported by

connective tissues; contains nerves to the heart

and coronary blood vessels

The entire cardiac structure (the heart and the beginnings

of the great vessels) is housed in a fibroserous sac called

the pericardial sac. Under normal conditions, the sac fits

snugly around the heart, leaving space only for about 50 mL

of lubricating fluid.

Blood Flow

The septum effectively divides the heart into right and left

sides to form two separate pumps. The right side pumps

blood through the lungs, and the left side maintains

circulation through the body (Figure A4). The walls of the

left ventricle are three times thicker than those of the right

side because it takes more pressure to reach distal parts of

the body.

The two pumps of the right and left heart function in

close syncopation. This is a closed system, so the blood continues interminably in a cycle:

• The right atrium receives blood from distal parts of

the body by way of the superior or inferior vena cava.

• Blood passes through the tricuspid valve to the right

ventricle.

• The right ventricle pumps the blood out the pulmonic

valve to the pulmonary artery and on to the lungs for a

new supply of oxygen.

• Oxygenated blood returns via the pulmonary vein to

the left atrium.

• From the left atrium, it passes through the mitral valve

and into the left ventricle.

• When the left ventricle contracts, the oxygenated blood

is ejected through the aortic valve to the aorta and

distal body tissues.

Heart Valves

To keep all the blood flowing in the same direction, the

heart has two sets of one-way valves. The first two, called

the atrioventricular valves, are located at each of the two

openings between the atria and the ventricles. The tricuspid

valve lies between the right atrium and right ventricle, and

the mitral (also called bicuspid) valve separates the left atria

and left ventricle. The second pair is called the semilunar

valves. One is located at each of the two exits leading from

the ventricles into the great vessels. The pulmonic valve is

at the exit from the right ventricle to the pulmonary artery,

and the aortic valve is at the exit from the left ventricle to

the aorta (Figure A5).

All of the valves consist of leaflets that open and close

in response to changing pressures within the chambers.

Structures called chordate tendineae connect the valve

leaflets to papillary muscles that open and close the valves

and prevent backflow. The two atrioventricular valves open

together to allow blood to flow into the ventricles. Then they

close together, and the aortic and pulmonic valves open

together, allowing blood to pass out of the heart.

Heart Sounds

Sounds associated with blood flow through heart chambers

and the closing of heart valves can be heard with the aid of a

stethoscope placed against the chest wall. The normal heart

has four distinct sound components.

Figure A3 Walls of the Heart

Epicardium (houses

coronary vessels and nerves)

Pericardial

 Fluid

Pericardium

Pleural

 Cavity

Pleura

Endocardium (houses

electrical system)

Heart

Chamber

Lungs Myocardium

Cardiac Anatomy and Physiology 457

1. The first heart sound (S )1 is associated with the closure

of the mitral and tricuspid valves and corresponds to

the onset of ventricular systole. Since mitral closure

precedes tricuspid closure by a split second, S1 has

two separate components, but these are generally not

audible.

2. The second heart sound (S )2 is associated with the

closure of the aortic and pulmonic valves. S2 also has

two components: the first is closure of the aortic valve,

and the second is the pulmonic. The first and second

heart sounds are normal findings.

3. The third heart sound (S )3 is a sign of pathology in an

adult. It occurs early in ventricular diastole, during the

phase of rapid ventricular filling.

4. The fourth heart sound (S )4 is related to atrial contraction

that is more forceful than normal.

Figure A4 Flow of Blood through the Body

Right

Heart

Left

Heart

Ascending Aorta

Descending

 Aorta

Inferior

Vena Cava

Pulmonary

Vein

Pulmonary

Artery

Superior Vena Cava

To

Body

To

Lungs

From

Lungs

From

Body

RIGHT HEART

pumps blood

• from body

• to lungs

LEFT HEART

pumps blood

• from lungs

• to body

458 Appendix A

Gallop Rhythms

Gallop rhythms are so called because the heart sounds are

grouped together so they sound like galloping horses. There

are three distinct types of gallop rhythms: ventricular gallop

rhythm, due to an exaggerated third heart sound; atrial gallop

rhythm, which occurs late in diastole or just before systole;

and summation gallop rhythm, heard when a tachycardia is

so rapid that the third and fourth heart sounds are blended

into one.

Murmurs

Murmurs reflect turbulence that can be caused by high

flow rates, damaged valves, dilated chambers or vessels, or

backward flow through a regurgitant valve. Murmurs are

described by timing, intensity, quality, pitch, location, and

radiation.

Systole and Diastole

In the first phase of a cardiac cycle the atria are at rest,

allowing blood to pour in from the body and lungs. This

phase is called atrial diastole. As the pressure rises, the

tricuspid and mitral valves open to allow blood to pass into

the relaxed ventricles. Next, the atria contract (atrial systole)

to fill the ventricles. The period during which the ventricles

are relaxed and filling is called ventricular diastole. As the

pressures equalize, the tricuspid and mitral valves close

and the aortic and pulmonic valves open. The ventricles

contract (ventricular systole) and eject blood from the heart,

into either the pulmonary system or the distal circulation

(Figure A6).

Coronary Circulation

The heart is never without blood inside its chambers, but

it can’t use this blood for its own nourishment. The

tissues of the heart itself have a separate blood supply

that flows on the outside of the heart to provide oxygen to

heart tissues.

As blood leaves the left ventricle and enters the aorta

for general circulation, it comes immediately to the coronary arteries, which siphon off a share of oxygenated

blood to supply the heart muscle itself. There are two main

vessels, the left and right coronary arteries, each supplying the major portion of their respective ventricles. The

left coronary artery quickly branches into the anterior

descending artery, which supplies the anterior surface of

the heart, and the circumflex artery, which passes around

to the left and back between the left atrium and left ventricle (Figure A7).

Occasionally, the circumflex branch continues around

to supply the back side of the heart, including the septum.

In such a case, the coronary circulation would be considered dominant left. However, in 80 percent of people, the

right coronary artery supplies the posterior side of the heart

and interventricular septum. This is called a dominant

right heart.

Figure A5 Heart Valves

Aortic Valve

Tricuspid Valve Mitral Valve

Pulmonic Valve

Cardiac Anatomy and Physiology 459

Deoxygenated blood is returned to general circulation

by way of cardiac veins, which empty into the coronary

sinus, located within the right atrium.

Surfaces of the Heart

The heart has four surfaces, or planes. The anterior surface

faces forward, abutting the chest wall. On the opposite

plane, facing the spine, is the posterior surface. The inferior

(diaphragmatic) surface refers to the under portion of the

heart that rests against the diaphragm. The lateral surface is

the side wall, on the side above the diaphragmatic surface

(Figure A8).

Figure A6 Systole and Diastole

Atrial Diastole

 Atria are at rest.

Ventricular Diastole

Ventricles are at rest.

ATRIAL SYSTOLE

VENTRICULAR SYSTOLE

As ventricles finish

contracting, the atria

fill with blood from

Vena Cavae and

Pulmonary Veins.

Ventricles contract, forcing blood

through Pulmonic and Aortic Valves

to lungs and body.

Pulmonic and Aortic Valves open.

Mitral and Tricuspid Valves open.

When ventricles are completely filled,

Mitral and Tricuspid Valves close.

When atria are completely filled,

Pulmonic and Aortic Valves close.

Atria contract, forcing blood through

Mitral and Tricuspid Valves into

ventricles.

1 2

3

4

460 Appendix A

Figure A7 Coronary Circulation

FRONT

Circumflex

Left Coronary

Artery

Right Coronary

Artery

Right

Coronary

Artery

Circumflex Branch of

Left Coronary Artery

Anterior

Descending

Branches

BACK

Cardiac Anatomy and Physiology 461

Figure A8 Surfaces of the Heart

Posterior Wall

Anterior Wall

Anterior

Surface

Left

Ventricle

Right

Ventricle

Inferior

(Diaphragmatic)

Surface

Sternum

Spine

Lateral

Surface

Inferior

(Diaphragmatic)

Surface

Lateral

Wall

462

Overview

IN THIS APPENDIX, you will be exposed to the clinical importance of each of the basic cardiac

arrhythmias you learned in earlier chapters. You will learn about cardiac output, and how it is

affected by arrhythmias, and about the symptoms produced when it is impaired. You will also

learn general treatment principles that apply when arrhythmias cause clinical problems. Then, for

each arrhythmia, you will find out its significance and clinical presentation.

Pathophysiology and

Clinical Implications

of Arrhythmias

Appendix B

Pathophysiology and Clinical Implications of Arrhythmias 463

Pathophysiology

Arrhythmias are manifestations of electrical activity in the

heart. Ideally, each electrical impulse results in a mechanical

contraction of the heart to pump blood and produce a pulse.

Arrhythmias cause problems when this process breaks

down. When a rhythm fails to produce adequate pulses, the

patient begins to have symptoms. Symptoms arise when

arrhythmias reduce cardiac output, the volume of blood

pumped by the heart.

Cardiac Output

Cardiac output is defined as the total volume of blood

pumped by the heart in one minute. If you measured the

volume pumped during each ventricular contraction (called

stroke volume) and multiplied that by the number of contractions (heartbeats) per minute, you would have a measured

cardiac output. The formula for measured cardiac output is:

Heart Rate S × = troke Volume Cardiac Output

Anything that alters either heart rate or stroke volume

will also affect cardiac output. Arrhythmias have the ability to

lower cardiac output (and thus cause symptoms) in two ways:

Heart Rate: Any rhythm with an extreme rate (either

bradycardia or tachycardia) can reduce cardiac

output.