Interpretation of Normal ECG *medical

7/28/2019 Interpretation of Normal ECG *medical

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ECG or EKG:

Interpretation of normalECG

Dr. Kyaw Min


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To get differentperspectives ofthe heart
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Electrocardiograph

electrodes, electrode cables

amplifiers filters,

control modules,

paper recordingmodule

special graph paper


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V1-V2 anteroseptal wall II, III, aVF inferior wall

V3-V4 anterior wall I, aVL lateral wall

V5-V6 anterolateral wall V1-V2posterior wall(reciprocal)

Electrocardiograp

hic view of theheart


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A normal adult 12-lead ECG. Sinus rhythm is present with a heart rate of 75

beats per minute.


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Waves

Positive

Negative

Segments

Intervals


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Paper speed: 25 mm/secVoltage

5 mm

= 0.2s

5 mm= 0.5mV

Voltagecalibration:

2 largesquares (10mm)

= 1 mV

1 large square = 0.2 s

300 large squares = 300 x 0.2 s = 60s(1 min).
http://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svghttp://en.wikipedia.org/wiki/Image:ECG_Paper_v2.svg


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vertical

horizontal

Each large(5mm)square : 0.5mV0.2s

Each small(1mm)square : 0.1mV0.04s

t


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aves, nterva s ansegments

in normal ECG
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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wave0.08 to 0.1 s; 0.25 mV or less)

represents the wave ofdepolarization that spreadsfrom SA node throughoutthe atria.

upright in all leads; butinverted in aVR.

atrial repolarization isubmerged in QRS complex)
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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QRS complex(0.06 to0.1 s)

(1- 3 small squares)-represents ventriculardepolarization.

- In most people, QRS

complex is tallest in leadII, but in leads I and III, itis also predominantlyupright (i.e. R wave is

greater than S).

-Prolonged QRS complex(> 0.1s) in Bundle

branch block
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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Q waveSmall septal Q wave in

any of leads II, aVL, or V5 V6, usually less than 3 mmdeep and less than 1 mmacross.

-represents the normaldepolarization ofinterventricular septumfrom left to right.

-A small Q wave is also

common in lead III innormal eo le in which


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T wave-represents ventricular

repolarization- In a normal ECG, Twave is alwaysinverted in aVR, and

often in V1, butusually upright in allthe other leads.


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U waveSometimes a small

U wave may beseen following Twave (lastremnants of

ventricularrepolarization andslow repolarizationof papillarymuscles)


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-R intervalormal range is 0.12 to 0.2 s

3 5 small squares)

the period of timerom the onset of theP wave to the beginning

f the QRS complex.represents the timeaken for depolarizationf atria, and conduction

through AV node andis-Purkinje system.

long PR interval reflects slow conduction

eart block, bradyarrhythmia)
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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-T interval (0.2 to 0.4 s)represents the time for

both ventriculardepolarization andrepolarization.

At high heart rates,Q-T interval decreases.

Long QT syndrome(K+ channel mutation,yocardial ischemia

lectrolyte abnormalities)


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T segmentthe part between S wave and

T wave.is the time at which theentire ventricle is depolarized.

hould be horizontal andisoelectric.

oughly corresponds to

heplateau phase ofentricular depolarization

-Important for diagnosis of ventricular

ischemia (depressed or elevated)
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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segmentn elevation of the ST segment

the hallmark of an acuteyocardial infarction.orizontal ST segment depressionmore than 2mm indicates

chaemia.
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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Cardiac axis

Depolarization wave of theheart normally spreads through

the ventricles from 11 oclock

to 5 oclock,

i.e. towards leads I, II and III.

So the deflections in lead VR

are normally mainly downward

(negative) and lead II mainly

upward (positive).

Direction of the axis can bederived most easily from the

QRS complex in leads

I, II and III.


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The cardiac axis

By near-consensus, the normal QRS

axis is defined as ranging from -30

to +90.

-30 to -90 is referred to as a left axis

deviation (LAD)+90 to +180 is referred to as a right

axis deviation (RAD)

Abnormalities of axis can hint at:Ventricular enlargement and/or

conduction defects (i.e. hemiblocks)


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If right ventricle becomes hypertrophied, the axiswill swing

towards the right : the deflection in lead I becomesnegative and

Right axis deviation


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When left ventricle becomes hypertrophied, the axismay swing

to the left, so that the QRS complex becomesredominantl

Left axis deviation


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Uses of ECG

Recording of rate and rhythm diagnosis of cardiac arrhythmias

detection of conduction

abnormalities (e.g. heart block,accelerated conduction)

screening tool for ischaemic heart

disease (during a cardiac stresstest)


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Uses of ECG

It guides therapy and riskstratification for patients withsuspected acute myocardial

infarction

It helps detect electrolytedisturbances (e.g.

hyperkalaemia andhypokalaemia)


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RR interval = one ventricular cycle Ventricularate heart rate

PP interval = one atrial cycle atrial rate
http://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svghttp://en.wikipedia.org/wiki/Image:SinusRhythmLabels.svg


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Heart Rate Determination Method 1

Most rates can be calculated this way. Find an Rwave on a heavy line (large box) count off

"300, 150, 100, 75, 60, 50"for each large box you land on until you reach the

next R wave. Estimate

the rate if the second R wave doesn't fall on aheavy black line.


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Heart Rate Determination Method 2

Use this method if there is a regularbradycardia,

i.e. - rate < 50.

If the distance between the two R waves is

too long to use the common method 300/[# large boxes between two R

waves].

The number of large boxes between first and second Rwaves = 7.5. Thus 300/7.5 large boxes = rate 40.


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Heart Rate = ?

Heart Rate = 300/5 = 60/min


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rate 100 = sinus tachycardia
http://www.ecglibrary.com/sbrady.htmlhttp://www.ecglibrary.com/stach.htmlhttp://www.ecglibrary.com/stach.htmlhttp://www.ecglibrary.com/sbrady.html


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Diagnosis of cardiac arrhythmias


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A normal 12-lead ECG and rhythm strip (Longlead II).Heart Rate = 300/4 = 75 bpm

Rhythm :

regular,

Sinus rhythm


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Cardinal features of Sinus rhythm

The P wave is upright in lead II,inverted in aVR

Each P wave is usually followed by aQRS complex

The heart rate is 60 99 beats/min

rate 100 = sinus tachycardia


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Abnormalities of cardiacrhythm

Look at the P waves and the widthof the QRS complex

Supraventricular rhythms havenarrow QRS complexes

Ventricular rhythms have wideQRS complexes (due to slower

pathway through the Purkinjefibers)


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Rate: 150 -250 /m

Rate: 250 -350 /m

Rate: 350+ /m

Abnormally shaped P wave

Arrhythmias

(saw-tooth waves)

(Abnormal P waves,one P wave/QRS)

Atrial fibrillation with a totally

irregular ventricular rate.

Atrial rate 300-500/min.


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Supraventricular rhythms Atrial tachycardia:

QRS complex rate greater than150/min;

Abnormal P waves, usually with short

PR intervals, usually one P wave perQRS complex, but sometimes P waverate 200-240/min with 2:1 block

Rate: 150 -250 /m

(Abnormal P waves,one P wave/QRS)


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Supraventricular rhythms

Atrial flutter: P wave rate 300/min,

saw-toothed pattern, 2:1, 3:1 or 4:1block

Rate: 250 -350 /m


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Supraventricular rhythms Atrial fibrillation:

the most irregular rhythm of all,

QRS complex rate characteristicallyover 160/min without treatment, butcan be slower

no P waves identifiable, but there is avarying completely irregular wavy

baseline

r


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Ventricularpremature beat(extrasystole)

Ventricular

tachycardia

(fast rate, no P wave,

wide bizarre QRS)

r

Arrhythmi

as

Ventricularfibrillation

(erratic, wavy

Defibrillator


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Ventricular extrasystoles:

Early QRS complex;

No P wave,

QRS complex wide (greater than 120ms);abnormally shaped; followed by a

compensatory pause Abnormally shaped T wave,

Next P wave is on time


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Ventricular tachycardia:

No P waves;

QRS complex rate greater than160/min; accelerated idioventricularrhythm

Wide bizarrely shaped QRS complex


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Ventricular fibrillation:

The most frequent cause of sudden

death in patients with myocardialinfarction

In the absence of emergency

treatment, lasts a few minutes; fatal Look at the patient, not the ECG

Ventricularfibrillation

(erratic, wavybaseline)

Defibrillator

C di l di i i


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CardiacPhysiology

Electrocardiography

Diagnosis

Ventricular Fibrillation

Ischemia

Electric Shock


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Detection of conductionabnormalities (e.g. heart block,accelerated conduction)


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First degree block:One P wave per QRS complexPR interval greater than .2 s


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Mobitz Type 2:(2:1 or 3:1 block)Occasional non-conducted beatsTwo or three P waves per QRS complex

Normal P wave rate,PR intervals are constantQRS is dropped intermittantly


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Progressive PR lengthening thennon-conducted P wave,And then repetition of the cycle


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Bundle Branch Block

If there is abnormal conductionthrough either the left or right bundlebranches (bundle branch block),

there will be a delay in thedepolarization of part of theventricular muscle

The extra time taken fordepolarization of the whole of theventricular muscle causes widening

of the QRS complex


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ird degree block (complete block):relationship between P waves and QRS complexes

wave and QRS march out separatelyually, wide QRS complexes

ual QRS complex rate less than 50/minmetimes narrow QRS complexes, rate 50-60/min


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Screening tool for ischaemic heartdisease (during a cardiac stresstest)


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Exercise or stress ECG

L d


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3 mm (0.3 mV) of horizontal ST-segment depression, indicating apositive test for ischemia.

After 4 min ofexercise

At rest

LeadV4:


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It guides therapy and riskstratification for patients withsuspected acute myocardialinfarction

Anterior Q wave infarction


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Deep Q waves, ST segment elevation. Later T inversion reciprocal ST depressions in leads III, and aVF.

Anterior Q wave infarction

Inferior Q wave infarction


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may be associated with reciprocal ST depressions in leadsV1 to V3.

Inferior Q wave infarction


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Myocardial Infarction

Sequence of ECG changes

Normal ECG

Raised ST segments

Appearance of Q waves

Normalization of ST segments

Inversion of T waves


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Ischemia T inversion

Injury ST segment elevation Infarct pathologic Q wave


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It helps detect electrolyte

disturbances (e.g. hyperkalaemiaand hypokalaemia)


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(Very tall, slender peaked T wave)

(T inversion, prominent U wave)

Electrolyte abnormalities


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Electrolyte abnormalities

Low K+

: T wave flattening and theappearance of a hump on the end ofthe T wave called a U wave.

High K+: tall, wide, peaked T waveswith the disappearance of the STsegment. The QRS complex may bewidened.

(Effects of abnormal magnesium levelsare similar.)

Low Ca2+: prolongation of the QTinterval


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How to report an ECG

Rate

Rhythm

Conduction intervals

Cardiac axis

A description of QRS complexes

A description of the ST segments andT wave


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DescriptionHeart rate 110/min,

Sinus rhythm

Normal PR interval (140 ms)

Normal QRS duration (120 ms)

Normal cardiac axis

Normal QRS complexes

Nor T waves

InterpretationNormal ECG


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Interpretation of Normal ECG *medical

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