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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