1) The ECG trace represents the electrical activity of the heart over one cardiac cycle and is made up of three distinct waves: the P wave from atrial depolarization, the QRS complex from ventricular depolarization, and the T wave from ventricular repolarization. 2) When interpreting an ECG, the clinician should check patient details, calibration, rate, rhythm, and abnormalities in each lead to identify any arrhythmias, conduction defects, or signs of myocardial infarction. 3) Common rhythms include normal sinus rhythm, sinus bradycardia/tachycardia, atrial fibrillation, ventricular tachycardia, and various types of heart block. ST segment elevation in certain leads

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ECG interpretation
ELENE KHURTSIDZE M.D.
Doctor of internal medicine

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Literature
 ESSENTIAL CLINICAL PROCEDURES, THIRD EDITION. © 2013 by
Saunders, an imprint of Elsevier Inc.
 Roberts: Roberts and Hedges' Clinical Procedures in Emergency
Medicine,6th ed. Copyright © 2013 Saunders, An Imprint of Elsevier
 The Royal Marsden manual of clinical nursing procedures/edited by Lisa
Dougherty and Sara Lister. – Ninth edition. © 2015

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■ 3 distinct waves are
produced during
cardiac cycle
■ P wave caused by
atrial depolarization
■ QRS complex caused
by ventricular
depolarization
■ T wave results from
ventricular
repolarization
ECG

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Elements of the trace
P wave = atrial depolarisation
QRS = ventricular epolarisation
T = repolarisation of the
ventricles

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Interpreting the ECG
 Check
 Name
 DoB
 Time and date
 Indication e.g. “chest pain” or “routine pre-op”
 Any previous or subsequent ECGs
 Is it part of a serial ECG sequence? In which case it may be numbered
 Calibration
 Rate
 Rhythm
 Axis
 Elements of the tracing in each lead

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Calibration
Check that your ECG is calibrated correctly
Height
 10mm = 1mV
 Look for a reference pulse which should be the rectangular looking
wave somewhere near the left of the paper. It should be 10mm (10
small squares) tall
Paper speed
 25mm/s
 25 mm (25 small squares / 5 large squares) equals one second

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Rhythm
Sinus Rhythm
Cardiac impulse originates from the sinus node. Every QRS
must be preceded by a P wave.
Sinus bradycardia
 Rhythm originates in the sinus node
 Rate of less than 60 beats per minute
Sinus tachycardia
 Rhythm originates in the sinus node
 Rate of greater than 100 beats per minute

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Normal Sinus Rhythm
 Originates in the SA node, follows appropriate conduction pathways.
 Rhythm: Regular
 Rate: 60-100 bpm
 Every P has a QRS and every QRS has a P
 PRI: 0 .12-0.20 seconds
 QRS: 0 .08 -0.12 seconds, narrow

15. + Sinus Bradycardia
 Originates in the SA note. Rate is slower.
 Rate: < 60 bpm
 Every P has a QRS and every QRS has a P
 PRI: 0.12 - 0.20 seconds
 QRS: 0.08 - 0.12 seconds, narrow

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Sinus Tachycardia
 Originates in the SA node.
 Rhythm: regular/fast
 Rate: > 100 bpm
 Every P has a QRS and every QRS has a P
 PRI: 0.12 - 0.20 seconds
 QRS: normal

17. + Premature Atrial complex (PAC)
 Originates in the atria.
 Rhythm: Irregular
 Rate: dependent on rhythm
 Every P has a QRS and every QRS has a P
 PRI: 0.12 -0 .20, may differ from underlying rhythm
 QRS: dependent on rhythm

18. + Atrial Fibrillation
 Rhythm: irregularly irregular
 Rate: slow or fast
 No identifiable P’s
 QRS usually narrow but may be wide with conduction defect
 F waves


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Atrial Fibrillation

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Atrial Flutter
 Conduction ratio to the ventricles 2:1 – 8:1. ( usually 2:1-4:1)
 If >150 bpm, may seriously compromise cardiac output.
 Treatment is rate control, cardioversion, surgical or catheter ablation.
 Rate: atrial rate 250-400 (generally 300bpm)

23. + Supraventricular Tachycardia/Atrial Tachycardia
 There are several different types of SVT/AT, depending on the site of reentry
(originates above ventricle) accessory pathway, atrioventricular node,
atrium
 Rhythm: Regular
 Rate: 150-250 bpm
 PRI: Dependent on location of “circuit”
 QRS: Normal, if accessory pathway used – prolonged (>.12) with delta wave
(WPW)

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25. + Junctional Rhythm
 An escape rhythm serves as a protective mechanism when higher
centers in the conduction system fail to fire.
 Rhythm: Regular
 Rate: 40 – 60 bpm
 P wave:
 Before QRS, inverted and P-R interval is < .12
 After QRS and usually inverted
 Absent
 QRS: < .12 seconds, unless prolonged by aberrant conduction

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27. Ventricular Tachycardia
QRS complexes are wide and irregular in shape
Usually secondary to infarction
Circuits of depolarisation are set up in damaged myocardium
This leads to recurrent early repolarisation of the ventricle leading to
tachycardia
As the rhythm originates in the ventricles, there is a broad QRS complex
Hence it is one of the causes of a broad complex tachycardia
Need to differentiate with supraventricular tachycardia with aberrant conduction

28. Ventricular Tachycardia
medics.cc

29. Ventricular fibrillation
Completely disordered ventricular depolarisation
Not compatible with a cardiac output
Results in a completely irregular trace consisting of broad QRS complexes of varying
widths, heights and rates

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31. + First Degree AV Block
 Occurs when impulses from the atria are consistently delayed during conduction through the
AV node.
 First degree AV block is a constant and prolonged PR interval.
 Rhythm: Regular
 Every P has a QRS and every QRS has a P
 PRI: > .20 seconds
 QRS < .12

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Second Degree AV Block
Mobitz I
Progressive delay at the AV node until the impulse is completely
blocked.
No treatment needed if patient is asymptomatic
Rhythm: Irregular
PR: progressive lengthening of PRI until dropped beat.
 (long, longer, drop)
QRS is usually < .12

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Second Degree AV Block, Mobitz II
 Because the ventricle rate is slow, cardiac output may be decreased
 May progress to third degree heart block.
 Occurs when some impulses from SA node fail to reach the ventricles
 Usually occurs with AMI, degenerative changes in conduction, progressive CAD
 Problem usually occurs at the Bundle of HIS or it’s branches
 Rhythm is irregular (because of dropped beats)
 PRI: remains constant until a block of the AV conduction, resulting is a P wave not
being followed by a QRS
 Is there a P for every QRS (YES); is there a QRS for every P (NO)?

34. + Third Degree Heart Block
 No conduction through the AV node (“divorced heart”).
 Rhythm is regular (ventricular and atrial, but at diff. rates)
 Rate:
 Atrial: 60 to 100
 Ventricular 40 to 60
 PRI: will vary with no pattern or regularity
 QRS: origin of impulse determines QRS width.
 From AV node: QRS will be normal
 From Purkinje system: QRS will be wide, rate < 40

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Myocardial infarction
 Within hours:
 T wave may become peaked
 ST segment may begin to rise
 Within 24 hours:
 T wave inverts (may or may not persist)
 ST elevation begins to resolve
 If a left ventricular aneurysm forms, ST elevation may persist
 Within a few days:
 pathological Q waves can form and usually persist

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Myocardial infarction
The leads affected determine the site of the infarct
 Inferior II, III, aVF
 Anteroseptal V1-V4
 Anterolateral V4-V6, I, aVL
 Posterior : Tall wide R and ST↓ in V1 and V2

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The ST segment
• If the ST segment is elevated but slanted, it may not
be significant
• If there are raised ST segments in most of the leads, it
may indicate pericarditis – especially if the ST
segments are saddle shaped. There can also be PR
segment depression

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medics.c
Acute Anterior MI
STelevation

41. + Inferior MI
STelevation

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