The Basics of The Basics of ECG ECG
InterpretationInterpretationDr Tim SmithDr Tim Smith
SummarySummary
Cardiac conducting system and the Cardiac conducting system and the ECG waveformECG waveform
The normal ECGThe normal ECG Abnormalities of conductionAbnormalities of conduction Heart RhythmsHeart Rhythms QT prolongationQT prolongation Normal VariantsNormal Variants
Cardiac DepolarisationCardiac Depolarisation
Originates in pacemaker cells (automaticity).Originates in pacemaker cells (automaticity). Spreads along defined pathways.Spreads along defined pathways. Causing co-ordinated muscular contraction.Causing co-ordinated muscular contraction.
Electrical signal from depolarisation Electrical signal from depolarisation detectable at body surface. (1 mV cf. 90 mV detectable at body surface. (1 mV cf. 90 mV @ cell)@ cell)
This is the ECG.This is the ECG.
The Cardiac Conducting The Cardiac Conducting SystemSystem
Anatomy of the ECGAnatomy of the ECG
The Limb LeadsThe Limb Leads
I, II, VL - L lateral I, II, VL - L lateral surfacesurface
VF, III - Inferior VF, III - Inferior surfacesurface
VR - R atriumVR - R atrium
Cardiac AxisCardiac Axis Lead II often used Lead II often used
for rhythm strips.for rhythm strips.
The Chest LeadsThe Chest Leads
VV1+21+2 - R - R VenticleVenticle
VV3+43+4 - Septum - Septum VV5+65+6 - L - L
VentricleVentricle
Bundle Branch Bundle Branch BlocksBlocks
Ischaemia Ischaemia (esp. V(esp. V55))
The Normal ECGThe Normal ECG
Characteristics of the Characteristics of the Normal ECGNormal ECG
RateRate 50-100 bpm50-100 bpm Sinus rhythmSinus rhythm Cardiac Axis -30º to +90ºCardiac Axis -30º to +90º P P <120 ms<120 ms PRPR <200 ms<200 ms QRSQRS <120 ms<120 ms QTQT Male <0.43 s Female <0.45 sMale <0.43 s Female <0.45 s STST isoelectricisoelectric
Calculating Heart RateCalculating Heart Rate
Standard ECG speed is 25 mm.sStandard ECG speed is 25 mm.s -1-1
Heart Rate = 300/# big squaresHeart Rate = 300/# big squares
300/3.8=79 bpm
Abnormalities of Abnormalities of conductionconduction
At the AVN = Heart BlockAt the AVN = Heart Block 1st degree1st degree 2nd degree2nd degree 3rd degree3rd degree
In the His/Purkinje system = Bundle In the His/Purkinje system = Bundle Branch BlockBranch Block
LBBBLBBB RBBBRBBB
First Degree Heart BlockFirst Degree Heart Block Prolonged PR interval >200 ms (5 small sq.)Prolonged PR interval >200 ms (5 small sq.)
Slow conduction through the AVNSlow conduction through the AVN Not itself importantNot itself important May indicate disease:May indicate disease:
RARA IHDIHD Dig. ToxicityDig. Toxicity
Second Degree Heart BlockSecond Degree Heart Block
Mobitz Type I (Wenkebach)Mobitz Type I (Wenkebach)
Increasing PR interval preceding unconducted Increasing PR interval preceding unconducted P.P.
Does not usually cause symptoms.Does not usually cause symptoms.• May indicate disease (RA, IHD, Dig.).May indicate disease (RA, IHD, Dig.).• Usually benignUsually benign
Second Degree Heart BlockSecond Degree Heart Block
Mobitz Type IIMobitz Type II
Fixed PR interval with some unconducted P Fixed PR interval with some unconducted P waves.waves.
May occur with fixed ratio eg. 2:1 blockMay occur with fixed ratio eg. 2:1 block Indicates underlying disease.Indicates underlying disease. May cause symptoms/precede complete block.May cause symptoms/precede complete block.
Third Degree Third Degree (Complete) (Complete) Heart BlockHeart Block No relationship between P & QRSNo relationship between P & QRS
QRS often wideQRS often wide
Atrioventricular dissociationAtrioventricular dissociation Impairs cardiac performance.Impairs cardiac performance.
Left Bundle Branch Left Bundle Branch BlockBlock
Characteristic, widened QRS in chest leadsCharacteristic, widened QRS in chest leads Will not cause symptoms itselfWill not cause symptoms itself Always indicates underlying heart diseaseAlways indicates underlying heart disease Makes ECG interpretation difficult or Makes ECG interpretation difficult or
impossibleimpossible
W i LL ia M
Right Bundle Branch Right Bundle Branch BlockBlock
Characteristic, widened QRS in chest leadsCharacteristic, widened QRS in chest leads May indicate right heart diseaseMay indicate right heart disease Can occur in normal individualsCan occur in normal individuals
Partial RBBB is always normal.Partial RBBB is always normal.
M a RR o W
Heart RhythmHeart Rhythm
Always ask:Always ask:
What is the QRS width?What is the QRS width? <120ms => Supraventricular source<120ms => Supraventricular source >120 ms => Ventricular source (or BBB)>120 ms => Ventricular source (or BBB)
Is there a P wave?Is there a P wave? Is the rhythm Is the rhythm
regular/irregular/irregularly regular/irregular/irregularly irregular?irregular?
Supraventricular Supraventricular Rhythms (1)Rhythms (1)
Normal Sinus RhythmNormal Sinus Rhythm
Supraventricular Supraventricular Rhythms (2)Rhythms (2)
(Respiratory) Sinus Arrhythmia(Respiratory) Sinus Arrhythmia
Inspiration Expiration
Supraventricular Supraventricular Rhythms (3)Rhythms (3)
Supraventricular EctopicSupraventricular Ectopic
Supraventricular Supraventricular Rhythms (4)Rhythms (4)
Junctional Escape BeatJunctional Escape Beat
Supraventricular Supraventricular Rhythms (5)Rhythms (5)
Sinus TachycardiaSinus Tachycardia
Supraventricular Supraventricular Rhythms (6)Rhythms (6)
Junctional TachycardiaJunctional Tachycardia
Supraventricular Supraventricular Rhythms (7)Rhythms (7)
Atrial FibrillationAtrial Fibrillation
Supraventricular Supraventricular Rhythms (8)Rhythms (8)
Atrial FlutterAtrial Flutter
Ventricular Rhythms (1)Ventricular Rhythms (1)
Ventricular Ectopic and CoupletVentricular Ectopic and Couplet
Ventricular Rhythms (2)Ventricular Rhythms (2)
Ventricular BigeminyVentricular Bigeminy
Ventricular Rhythms (3)Ventricular Rhythms (3)
Ventricular TachycardiaVentricular Tachycardia
Ventricular Rhythms (4)Ventricular Rhythms (4)
Ventricular FibrillationVentricular Fibrillation
QT ProlongationQT Prolongation QT represents the ventricular refractory periodQT represents the ventricular refractory period Normal <450 ms (ish)Normal <450 ms (ish) Risk of prolongation...Risk of prolongation...
Torsades de Pointes - potentially lethal.
QT ProlongationQT Prolongation
? How long is too long? How long is too long Affected by temperature, gender, Affected by temperature, gender,
heart rateheart rate Diurnal variation up to 70 msDiurnal variation up to 70 ms Numerous drugs:Numerous drugs:
CisaprideCisapride TerfenadineTerfenadine Total of 48 listed as causing TdP by FDATotal of 48 listed as causing TdP by FDA
Normal VariantsNormal Variants Always normal:Always normal:
Sinus ArrhythmiaSinus Arrhythmia Supraventricular ExtrasystolesSupraventricular Extrasystoles Partial RBBBPartial RBBB
Often normal:Often normal: Sinus Bradycardia (and pauses in athletes)Sinus Bradycardia (and pauses in athletes) First Degree Heart BlockFirst Degree Heart Block Ventricular ExtrasystolesVentricular Extrasystoles Left/Right Axis DeviationLeft/Right Axis Deviation RBBBRBBB
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