Ebook The only EKG book you’ll ever need (9/E): Part 1

Part 1 book “The only EKG book you’ll ever need” has contents: The basics, hypertrophy and enlargement of the heart, arrhythmias, conduction blocks, combining right bundle branch block and hemiblocks, electricity and the heart, the cells of the heart,… and other contents.

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This work is no substitute for individual patient assessment based upon healthcare professionals' examination of each patient and consideration of, among other things, age, weight, gender, current or prior medical conditions, medication history, laboratory data and other factors unique to the patient The publisher does not provide medical advice or guidance and this work is merely a reference tool Healthcare professionals, and not the publisher, are solely responsible for the use

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Given continuous, rapid advances in medical science and health information, independent

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For Nancy, Ali, Jon, and Tracey too–as well as for everyone toiling in the health care profession, trying to make people’s lives happier and healthier.

This book is about learning It’s about keeping simple things simple, and complicated things clear, concise and, yes, simple, too It’s about getting from here to there without scaring you to death, boring you to tears, or intimidating your socks off It’s about turning ignorance into knowledge, knowledge into wisdom, and all with a bit of fun.

If I were writing this today, I would probably reword that business about thesocks, but the sentiments remain and are, I hope, ones you share New materialhas been added as new developments—and there have been many—have calledfor it, and everything is always discussed within its proper clinical context byputting you, the reader, right in the middle of real life situations EKG’s are notused in isolation; they are just one piece—albeit an important piece—of thepuzzle that every patient presents and that you and I have to figure out over andover again

I want to offer a very special thanks to Dr Adam Skolnick, M.D., AssociateProfessor of Medicine, Leon H Charney Division of Cardiology, NYU LangoneMedical Center, whose keen editorial eye, incisive analysis, and unsurpassedexpertise are the best guarantee that you will be reading the most current, clear,and accurate text that anyone could hope for And allow me to add a shout out to

Dr Jeffrey Lorin, Assistant Professor of Medicine at NYU Medical Center, whograciously opened up his world-class collection of EKG’s so that we all couldbenefit.

1 |

Getting Started

In this chapter you will learn:

not a thing, but don’t worry There is plenty to come Here is yourchance to turn a few pages, take a deep breath or two, and getyourself settled and ready to roll Relax Pour some tea Begin

On the opposite page is a normal electrocardiogram, or EKG.1 By the time youhave finished this book—and it won’t take very much time at all—you will beable to recognize a normal EKG almost instantly Perhaps even more

importantly, you will have learned to spot all of the common abnormalities thatcan occur on an EKG, and you will be good at it!

or the extraordinary jazz interplay of Keith Jarrett’s Standards Trio

There’s just not that much going on

The EKG is a tool of remarkable clinical power, both because of the ease withwhich it can be mastered and because of the extraordinary range of situations inwhich it can provide helpful and even critical information One glance at anEKG can diagnose an evolving myocardial infarction, identify a potentially life-threatening arrhythmia, pinpoint the chronic effects of sustained hypertension orthe acute effects of a massive pulmonary embolus, or determine the likelihood ofunderlying coronary artery disease in a patient with chest pain.

Michelangelo’s David.

The nine chapters of this book will take you on an electrifying

voyage from ignorance to dazzling competence You will amaze yourfriends (and, more importantly, yourself) The road map you will

follow looks like this:

Chapter 1: You will learn about the electrical events that

generate the different waves on the EKG, and—armed with thisknowledge—you will be able to recognize and understand thenormal 12-lead EKG

pacemakers

Chapter 5: You will see what happens when the heart’s electricalcurrent bypasses the usual channels of conduction and arrivesmore quickly at its destination

Chapter 6: You will learn to diagnose ischemic heart disease:myocardial infarctions (heart attacks) and angina (pain that

results when regions of the heart are deprived of oxygen)

Chapter 7: You will see how various other cardiac and

noncardiac phenomena can alter the EKG

Chapter 8: You will put all your newfound knowledge togetherinto a simple method for reading all EKGs

Chapter 9: A few practice strips will let you test your knowledgeand revel in your astonishing skill

The whole process is straightforward and should not be the least bit

intimidating Intricacies of thought and great leaps of creative logic are notrequired

This is not the time for deep thinking

ECG—in America, where obstinacy is too often a virtue, we have clung to the EKG acronym, although even here the bonds of tradition are slowly loosening So please calm down You don’t panic when you are invited to a barbecue instead of a barbeque, do you?

how the electrical current in the heart is generated

how this current is propagated through the four chambers of theheart

that the movement of electricity through the heart produces

predictable wave patterns on the EKG

how the EKG machine detects and records these waves

that the EKG looks at the heart from 12 different perspectives,providing a remarkable three-dimensional electrical map of theheart

that you are now able to recognize and understand all the lines

and waves on the 12-lead EKG

that trusting the EKG machine to interpret your patient’s EKG is

7 |nothing but an invitation to trouble!

Electricity and the Heart

Electricity, an innate biologic electricity, is what makes the heart go The EKG isnothing more than a recording of the heart’s electrical activity, and it is throughperturbations in the normal electrical patterns that we are able to diagnose manydifferent cardiac and noncardiac disorders

All You Need to Know About Cellular Electrophysiology in a Few Brief Paragraphs

Cardiac cells, in their resting state, are electrically polarized; that is, their insidesare negatively charged with respect to their outsides This electrical polarity ismaintained by membrane pumps that ensure the appropriate distribution of ions(primarily potassium, sodium, chloride, and calcium) necessary to keep theinsides of these cells relatively electronegative These ions pass into and out ofthe cell through special ion channels in the cell membrane

depolarization that can be transmitted across the entire heart This wave of

depolarization represents a flow of electricity, an electrical current, that can bedetected by electrodes placed on the surface of the body

After depolarization is complete, the cardiac cells restore their resting polarity

through a process called repolarization Repolarization is accomplished by the

membrane pumps, which reverse the flow of ions This process can also bedetected by recording electrodes

All of the different waves that we see on an EKG are manifestations of thesetwo processes: depolarization and repolarization

Pacemaker cells are small cells approximately 5 to 10 μm long, about the same

as the width of a single strand of a spider’s web These cells are able to

depolarize spontaneously over and over again The rate of depolarization isdetermined by the innate electrical characteristics of the cell and by externalneurohormonal input Each spontaneous depolarization serves as the source of awave of depolarization that initiates one complete cycle of cardiac contractionand relaxation

A pacemaker cell depolarizing spontaneously.

If we record one electrical cycle of depolarization and repolarization from a

spontaneous depolarization, a new action potential is generated, which in turnstimulates neighboring cells to depolarize and generate their own action

epinephrine and norepinephrine, accelerates the sinus node, whereas vagalstimulation slows it) and the demands of the body for increased cardiac output(exercise raises the heart rate, whereas a restful afternoon nap lowers it)

Pacemaker cells are really good at what they do They will

continue firing in a donor heart even after it has been harvested fortransplant and before it has been connected to the new recipient.The transplanted heart, devoid of normal vagal stimulation (the

(sympathetic stimulation, cardiac disease, etc.) stimulates its

automatic behavior This topic assumes greater importance later on

and is discussed under Ectopic Rhythms in Chapter 3.

Electrical conducting cells are long, thin cells Like the wires of an electrical

circuit, these cells carry current rapidly and efficiently to distant regions of theheart They are, in effect, the electrical highway of the heart

Time and Voltage

myocardial cells, which make up the vast bulk of the heart Pacemaker activity

and transmission by the conducting system are generally not seen on the EKG;these events simply do not generate sufficient voltage to be recorded by surfaceelectrodes

The waves produced by myocardial depolarization and repolarization arerecorded on EKG paper and, like any wave, have three chief characteristics:

The horizontal axis measures time The distance across one small squarerepresents 0.04 seconds The distance across one large square is five timesgreater, or 0.2 seconds

The vertical axis measures voltage The distance along one small squarerepresents 0.1 mV, and along one large square, 0.5 mV

The sinus node fires spontaneously (an event not visible on the EKG), and awave of depolarization begins to spread outward into the atrial myocardium,much as if a pebble were dropped into a calm lake Depolarization of the atrialmyocardial cells results in atrial contraction

depolarizes spontaneously The wave of depolarization then propagates through both atria, causing them to contract.

Once atrial depolarization is complete, the EKG again becomes electrically

The components of the P wave.

A Pause Separates Conduction From the Atria to the Ventricles

In healthy hearts, there is an electrical gate at the junction of the atria and theventricles The wave of depolarization, having completed its journey through theatria, is prevented from communicating with the ventricles by the heart valvesthat separate the atria and ventricles Electrical conduction must be funneledalong the interventricular septum, the wall that separates the right and left

ventricles Here, a structure called the atrioventricular (AV) node slows

conduction to a crawl This pause lasts only a fraction of a second

This physiologic delay in conduction is essential to allow the atria to finishcontracting before the ventricles begin to contract This clever electrical wiring

of the heart permits the atria to empty their volume of blood completely into theventricles before the ventricles contract

Like the sinus node, the AV node is also under the influence of the autonomicnervous system Vagal stimulation slows the current even further, prolonging thedelay, whereas sympathetic stimulation accelerates the current through the AVnode

pause, the EKG falls silent; there is no detectable electrical activity.

Ventricular Depolarization

After about one-tenth of a second, the depolarizing wave escapes the AV nodeand is swept rapidly down the ventricles along specialized electrical conductingcells

This ventricular conducting system has a complex anatomy but essentially

reflecting the greater intricacy of the pathway of ventricular depolarization.

called the QRS complex.

The Parts of the QRS Complex

The QRS complex consists of several distinct waves, each of which has a name.Because the precise configuration of the QRS complex can vary so greatly, a

5 If the entire configuration consists solely of one downward deflection, the

wave is called a QS wave.

Here are several of the most common QRS configurations, with each wavecomponent named

interventricular septum by the septal fascicle of the left bundle branch The rightand left ventricles then depolarize at about the same time, but most of what wesee on the EKG represents left ventricular activation because the muscle mass ofthe left ventricle is about three times that of the right ventricle

The initial part of the QRS complex represents septal depolarization Sometimes, this septal depolarization may appear as a small, discrete, negative deflection, a Q wave.

wave on the EKG, the T wave.

Note: There is a wave of atrial repolarization as well, but it coincides

prominent QRS complex

Ventricular repolarization is a much slower process than ventricular

depolarization Therefore, the T wave is broader than the QRS complex Itsconfiguration is also simpler and more rounded, like the silhouette of a gentlehill compared to the sharp, jagged, and often intricate contour of the QRS

complex Except with certain pathologic conditions, which we will explore later,the voltage of the T wave is less than that of the Q wave

Naming the Straight Lines

The different straight lines connecting the various waves have also been given

so on

What differentiates a segment from an interval? A segment is a straight lineconnecting two waves, whereas an interval encompasses at least one wave plus,

You might be wondering: if the QRS complex has a Q wave, shouldn’t the PRsegment be called the PQ segment, and the PR interval the PQ interval? Well,yes, but they’re not These straight lines are always called the PR segment and

PR interval no matter what the configuration of the QRS complex

The ST segment is the straight line connecting the end of the QRS complex