EKG Student

8/8/2019 EKG Student

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1. Review of the conduction system

2. EKG waveforms and intervals

3. EKG leads

4. Determining heart rate

5. Identify dysrhytmias


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The electrocardiogram (EKG) is a

representation of the electrical events of the

cardiac cycle.

Each event has a distinctive waveform, the

study of which can lead to greater insight into

a patients cardiac pathophysiology.


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Arrhythmias

Myocardial ischemia and infarction

Pericarditis

Chamber hypertrophy Electrolyte disturbances (i.e. hyperkalemia,

hypokalemia)

Drug toxicity (i.e. digoxin and drugs which

prolong the QT interval)


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Occurs when there are no positive or

negative electrical wave deflections.


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Is the first wave of the

cardiac cycle &represents atrial

depolarization. When

the SA node fires, the P

wave normally appearsrounded & symmetrical

. There is 1 P wave in a

normal cardiac cycle .

Disorders that change

atrial size cause

alterations in P wave

shape & size.


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Represents the time it takes the electrical impulse

to travel down the atrium to the AV node.

It starts at the beginning of the P wave & ends at

the beginning of the QRS complex.

Counting the number of small boxes horizontally

that the interval covers determines the length ofthe PR interval.

Normal PR interval is 0.12 to 0.20 seconds.


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Represents ventricular depolarization & is

composed of 3 waves, the Q, R, and S.Atrial repolarization occurs during the interval of

the QRS but is not seen because of powerful

ventricular activity. Presence of p wave in the

following cardiac cycle ind. Atrial repolarizationhas occurred.


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Q- first downward deflection after the P wave but

before the R wave.

R first upward deflection after the P wave.

S- last part of the QRS complex, w/c is the second

negative deflection after the P wave .

-ends when it returns to the isoelectric line.


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To measure the QRS interval, count the number of

boxes from the wave that begins the QRS complexto the end of the wave that completes the QRS

complex.

Measure from the beginning of the Q wave to the

end of the S wave.Normal QRS interval is < 0.12 seconds.


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Represents ventricular repolarization .

Resting state of the heart, when ventricles are

filling w/ blood & preparing to receive the next

impulse.

Starts at the next upward (positive) deflection,

after the QRS complex, & ends w/ a return to the

isoelectric line.


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Usually not

present .

Seen in patients

w/ hypokalemia,w/c is low serum K

level.


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Reflects the time from completion of a

contraction (depolarization) of myocardial

muscle for the next impulse.

Starts at the end of the QRS and ends at thebeginning of the T wave .

Changes in ST segment ind. Ischemia, injury

pattern suggestive of myocardial damage.

ST inversion/ depression----ischemia

ST segment elevates from the isoelectric

line-----------cardiac injury.


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1. Regularity of the rhythm- can be

determined by looking at the R-R interval on

the ECG.if the distance is the same, the

rhythm is regular.


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Six sec. method: used for irreg. rhythms or

rapid estimate.

At the top of ECG graph paper there are 3

vertical marks at 3-seconds intervals. Count thenumber of R waves in a sec. strips & multiply the

total by 10.(6 sec X 10= 60 sec.)

Count the number of small (0.04-sec.) boxes

between 2 R waves & divide that number into

1500.

or count large boxes & divide by 300.300/5= 60

used for regular rhythms.


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To make measuring waves easier:

Identify the isoelectric line as you measure

waveform tracings to help you determine the

type of wave. Try to find a wave that starts at the beginning of

1 small box. If the wave starts or ends in the

middle of a box, count it as 1-half of a box, w/c

is 0.02 sec.


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Is there 1 P wave for every QRS complex?

Are the P waves regular 7 constant?

Do the P waves look alike?

Are the p waves upright and in front of every

QRS complex?


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Is the PR interval normal?

Is the PR interval constant or varying?


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Is the QRS interval normal ?

Is the QRS interval constant?

Do the QRS complexes all look alike?


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Dysrhythmias abnormal, disordered , or

disturbed rhythm.

Arrhythmia- is an irregularity or loss of

rhythm


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Sinus rhythm- rhythm arising from the SA

node.

pacemaker of the heart, fires normally 60-100

bpm.1.Sinus Bradycardia-

2. Sinus tachycardia-


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Normal rhythm in aerobically trained athletes and during sleep

Sinus Bradycardia- slower than normal heart rate (less than 60

bpm).eg. MI, Digoxin, electrolyte imbalance.


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heart rate greater than 100 bpm. Phy. Activity, hemorrhage,

shock, fever, fear, epinephrine, atropine, anxiety.


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Atrial impulses faster than the SA node, they

become primary pacemaker.

Are usually faster than 100bpm & can exceed

200 bpm. When an impulse originates outsidethe SA node, P wave produced look different

from the rounded P waves from the SA

node(flatter, notched, or peaked), w/c ind.

that the SA

node is not controlling the heartrate.


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Rhythm : premature beats interrupts underlying rhythm where it

occurs.

Heart rate: depends on the underlying rhythm; if normal sinus

rhythm (60-100bpm).

P waves: early beat is abnormally shapes.

PR interval: usually appears normal, but premature beat could

have shortened or prolonged PE interval.

QRS interval: < 0.12 sec. ( ind. Normal conduction to ventricles)


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Atria contract , or flutter , at a rate of 250

to 350 bpm.

Classic characteristic: more than 1 P wave

before a QRS complex, a saw toothed patternof P waves, and an atrial rate of 250 to 350

bpm.

Heart rate: ventricular rate varies

P waves: Flutter or F waves w/ saw toothedpattern.

PR interval: none measurable.

QRS complex: < 0.12 seconds


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Rhythm: irregularly irregular

Heart rate: atrial rate not measurable:

ventricular rate under 100 is rapid ventricular

response; greater than 100 is rapid ventricularresponse

P waves: no identifiable P waves

PR interval: none can be measured because no P

waves are seen.QRS complex: 0.06 to 0.10 sec.


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AV block - is a conduction defect

within the AV junction that impairs

conduction of atrial impulses to

ventricular pathways.

Types:

1. First degree

2. Second degree

3. Third degree


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Characteristics:

1. Rate

1st degree 60 to 100 bpm or the

inherent ventricular rate.2nd degree rate is slowed, atrial rate

is 2 to 4 times faster than the ventricularrate

3rd degree rate is slowed, usually 40to 60 beats per minute or the inherentventricular rate


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2. P wave is normal & present in each type of

block

3. PR intervals:

1st

degree PR intervals are prolonged at0.20 second

2nd degree PR intervals may be

progressively lengthening

3rd

degree no relationship between Pwaves & QRS complexes exist, PR intervals

cannot be measured


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4. QRS complex

1st & 2nd degree normal

3rd degree QRS is widened

5. Conduction

1st degree is delayed in the AV junction2nd degree impulses are not regularlyconducted through the AV junction

3rd degree - all sinus impulses are blocked,conduction through the ventricles is abnormal

6. Rhythm is regular in each type of block


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Clinical Manifestations:

1st degree asymptomatic

2nd degree vertigo, weakness & irregular pulse

3rd degree hypotension, angina & heart failureNursing Management:

1st degree no treatment, discontinue causative

drug if indicated

2nd degree administer Atropine SO43rd degree Atropine SO4, pacemaker


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Premature Ventricular Contractions- originate

in the ventricles from an ectopic focus ( a

site other than the SA node)

Rhythm: depends on the underlying rhythm

Heart rate: depends on the underlyingrhythm.

P waves: absent before PVC QRS complex

PR interval: none for PVC

QRS complex: if PVC, it is greater than 0.11sec. ; T wave is in the opposite direction of

QRS complex( ie. QRS upright, T downward

or QRS downward, T upright).


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Rhythm: usually regular, may have some

irregularity.

Heart rate: 150-250 ventricular bpm; slow VT

is below 150bpm.

P waves: absent PR interval: none

QRS complex: greater than 0.11 sec

Sustained VT compromises cardiac output.

The severity of symptoms can inc. rapidly ifleft ventricle fails & complete cardiac arrest

results.


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Rhythm: chaotic & extremely irregular.

Heart rate: not measurable

P waves: none

PR interval: none

QRS complex: none

Pt. lose consciousness immediately . No

heart sounds, peripheral pulses, or BP,

indicative of circulatory collapse.


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Treatment for life-threatening ventricular

arrhythmias

Lead system placed via subclavian vein to

endocardium Pulse generator is implanted over pectoral

muscle


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Provide backup pacing for bradyarrhythmias

after defibrillation


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Electronic device used in place of SA node

Paces both the atrium as well as the

ventricle

Increases HR when appropriateUsed in management of heart failure,

symptomatic bradyarrhythmias, and

neurocardiogenic syncope


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After sensing system defects in lethal

arrhythmia, delivers shock to the patients

heart muscle

Initiate overdrive pacing of supraventricularand ventricular tachycardias


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Radiofrequency energy used to burn

(ablate) areas of conduction system as

treatment for tacharrhythmias

Used for AV nodal reentrant tachycardia tocontrol ventricular response to certain

tachyarrhythmias, and in atrial flutter


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Leads are electrodes which measure the

difference in electrical potential between

either:

. Two different points on the body. Two different points on the body(bipolar leads)(bipolar leads)

2. One point on the body and a virtual2. One point on the body and a virtual

reference point with zero electricalreference point with zero electricalpotential, located in the center of thepotential, located in the center of the

heart (unipolar leads)heart (unipolar leads)


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The standard EKG has 12 leads:

3 Standard Limb Leads

3 Augmented Limb Leads

6 Precordial Leads

The axis of a particular lead represents theThe axis of a particular lead represents the

viewpoint from which it looks at theviewpoint from which it looks at theheart.heart.


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Rule of 300

10 Second Rule


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Take the number of big boxes between

neighboring QRS complexes, and divide this

into 300. The result will be approximately

equal to the rate

Although fast, this method only works for

regular rhythms.


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It may be easiest to memorize the following

table:

# of big boxes# of big boxes RateRate

33

22 55

33

44 757555 66

66 55


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As most EKGs record 10 seconds of rhythm per

page, one can simply count the number of beats

present on the EKG and multiply by 6 to get the

number of beats per 60 seconds.

This method works well for irregular rhythms.


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33 x 6 = 198 bpm


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Refers to a state of unresponsiveness

following excitation of the cardiac muscle

cell. When stimulated, the muscle cell will

respond completely or not at all or none at

all principle .Absolute refractory period: No stimulus (no

matter how powerful) can excite the tissue, if

the cell is stimulated during this period, the

stimulus is rejected.


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Relative refractory period: some of the cells havereturned to their original state (repolarized) & a

strong stimulus can excite the tissue. This period

also referred as vulnerable period because an

impulse striking at this time can initiate lifethreatening dysrhythmias (ventricular tachycardia

& ventricular fibrillation)


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The electrical impulses originates in the SA

Node, specialized electrical cells called p-

cells (pacemaker cells) in the SA Nodedischarge impulses at a rate of 60-100/ min

in rhythmic fashion.

It controls the heart rate it is designated as

the pacemeker.


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Preload: Passive load that establishes the initial muscle

length of the cardiac fibers prior to contraction

Afterload: Sum of all loads against which the the myocardial

fibers must shorten during systole. (aortic

impedance, arterial R, PVR, intraventricular P,

mass and viscosity of blood in the great arteries)

Contractility: Speed and shortening capacity at a given

instantaneous load (inotropy)

Diastolic Compliance:The ability to fill at a given diast. P

HeartRate: Frequency of contraction


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Table of contents

Surface potentials

Zero potentials

Depolarization

Repolarization

Normal Voltages in the Electrocardiogram

ReferencesSurface potentials

ECGs are merely recordings of voltage differences between two electrodes on the body surface as afunction of time.

Zero potentials

During diastole, when the heart is relaxed, the cardiac cells are positively charged on the outside and

negatively charged on the inside. Electrodes on the skin do not detect voltage differences because all partsof the heart are equally polarized. Thus, the recording shows no deflection, you see the flat line,

isoelectric line on the ECG.

Depolarization

Depolarization causes a reversal of membrane potential in a cardiac cell. The outside of these cells is now

negatively charged with respect to ground. Thus, a potential difference exists between the depolarized


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Depolarization

Depolarization causes a reversal of membrane potential in a cardiac cell. The outside of these cells is now

negatively charged with respect to ground. Thus, a potential difference exists between the depolarized

cells and the neighbouring, nonexcited cells.

Surface electrodes record this potential difference, and the direction of its deflection depends on the

polarity of the electrodes.

When the entire heart has been depolarized, all of the cells are negatively charged outside. Bothelectrodes again "see" the same potential, and the galvanometer reading returns to zero.

Repolarization

Repolarization is the reverse process were cells get back to the zero potential.


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Normal Voltages in the Electrocardiogram

The recorded voltages of the waves in the normal electrocardiogram depend on the

manner in which the electrodes are applied to the surface of the body and how

close the electrodes are to the heart. When one electrode is placed directly over

the ventricles and a second electrode is placed elsewhere on the body remote from

the heart, the voltage of the QRS complex may be as great as 3 to 4 millivolts.

When electrocardiograms are recorded from electrodes on the two arms or on one

arm and one leg, the voltage of the QRS complex usually is 1.0 to 1.5 millivolt fromthe top of the R wave to the bottom of the S wave; the voltage of the P wave is

between 0.1 and 0.3 millivolt; and that of the T wave is between 0.2 and 0.3

millivolt.

By convention:

A wave of depolarization approaching the positive electrodes results in an upward

deflection of the EKG tracing.

A wave of depolarization approaching the negative electrodes results in an

downward deflection of the EKG tracing.

A wave of depolarization proceeding parallel to an electrode axis (the line

connecting two electrodes) produces the maximal deflection of that dipole.

A depolarization wave perpendicular to the electrode axis produces no net

deflection of the tracing (the positive and negative waves are equal).


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S r T. T , ., ., .

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