Upload
hoanghanh
View
266
Download
4
Embed Size (px)
Citation preview
ECG interpretation fundamentals and arrhythmia recognition principles
Robert M GowDepartment of PaediatricsUniversity of OttawaFaculty of Medicine
ECG fundamentals
R iReviewLead theory and wavefront activationU i l d bi l l dUnipolar and bipolar leadsDetermination of frontal plane axisD t i ti f h i t l l iDetermination of horizontal plane axisECG recognition of electrolyte imbalanceS t ti h t h th i itiSystematic approach to arrhythmia recognition
ECG fundamentals
HistoryyAugustus Waller (1856-1922)
First ECG 1887Labelled V1 V2 then ABCD
Willem Einthoven (1860-1927)PQRSTEinthoven’s triangle
Frank Wilson (1890 1952)Frank Wilson (1890-1952)Unipolar leads
ECG fundamentals
posteriorspine
left
anteriorElectrical field passes throughlungs, muscle, blood, fat
Detected at skinSpreads out from source (heart)
ECG fundamentals
•Skin resistance is critical to recording of electricalactivity
•Resistance due to dry, dead, horny layer of epidermis
•MegaOhm resistance at surface (1 million Ohms)
•Simple abrading of skin reduces resistance to 5000 Ohms
•Good electrodes reduce to 100 Ohms
ECG fundamentalsBipolar Unipolar
t
- +
remote zero
- + +
Records difference between-ve and +ve terminals
Records difference between+ve electrode and remote zerove and +ve terminals
-ve is subtracted from +veDifference is recorded
+ve electrode and remote zero
Impulse travelling towardselectrode causes a positiveelectrode causes a positivedeflection
ECG fundamentalsLead +ve -ve1 LA RA
RA LA ll LL RAlll LL LA
lead
LLGround True bipolar leadsActual voltage not knowng
ECG fundamentals
Einthoven’s Law
l +- l + lll = ll
lllll
--Simple check forl d i l tll
++
lead misplacement
++
ECG fundamentals
Chest lead exploring electrode - unipolar
ECG amplifierLARA
+ve
CG a p e
5000 Ohm - ve
Wilson central terminalLLLL
ECG fundamentals
Augmented limb leadsAugmented limb leads
unipolar limb leadsu po a b eadscompares one limb with the average of the other 2
For example lead aVRunipolar RA is positiveaverage of LA and LL is negativeaverage of LA and LL is negativeaVR equals the potential of right arm minus the mean of the potentials of left arm and left footp
ECG fundamentals
Lead theoryLead theoryVector: electrical forces have direction and magnitudeHeart vector - from activation and propagationp p gLead vector - orientation of leads to heart vector
3 vector conceptis an extremeis an extremesimplification
ECG fundamentals- - -
Frontal Plane+aVL -30o
+ aVR -150o
+ 1 0o150
-
--
+ ll 60o+lll 120o
+aVF 90o Hexaxial lead system
ECG fundamentals
Horizontal Plane Lead VectorsHorizontal Plane Lead Vectors
Posterior
V5
V6 0o
V3V4
V5
V1 V2V3
+ 90o
ECG fundamentals
vector away = negatived i i
2,3
1 3 1
vector towards = positiveequiphasic = 90o
1
2
11
2
ll
2 1 = septum2 = dominant LV3 = basal RV/LV
aVF1
31,2
3
ECG fundamentals
QRS axis estimationQRS axis estimation
actually estimating a “mean” or average electrical forcesmean force estimated by area under QRS complex
then these are plotted as vectors on the hexaxial graph
ECG fundamentals
QRS axis estimationQRS axis estimation
Thankfully, measuring the area is not necessary
The net amplitude of the QRS complexes can be usedi t dinstead.
+10 Resultant = (+10) + ( 4) = +6
-4
+10 Resultant = (+10) + (- 4) = +6
4
ECG fundamentals
Different methods for frontal plane QRS axisDifferent methods for frontal plane QRS axis
•Can take any 2 leads or all sixCan take any 2 leads, or all six
•Leads 1, aVF commonly used
•Lead with smallest or equiphasic complex identified, d i i i t l 90o t thi l dand axis is approximately 90o to this lead
ECG fundamentals
8
3
+5
153Lead l
15
6
aVF10
4
+6 aVF
Not perfect but good enough4Lead aVF
Not perfect, but good enough
ECG fundamentals
Horizontal Plane -Horizontal Plane
left t i
righti
V6 0o V6l fti ht
posteriorposterior- +
V4V5 left
anteriorrightanterior
V1 V2V3
V2+
ECG fundamentals
QRS axis
•affected by anatomic position of the hearty p
•properties of the cardiac conduction system
•developmental changes in RV/LV mass relationships
•conduction system most influential in mature heart
ECG fundamentalsElectrolyte abnormalities
HypokalaemiaHypokalaemiaST depressionlowering of T wavelowering of T waveincrease in U wave heightU > T suggests K < 2.7 mEq/l
HyperkalemiaTall thin T wavesTall thin T wavesPR prolongedQRS widensQP waves disappear
ECG fundamentals
Electrolyte abnormalities
ECG fundamentals
Electrolyte abnormalities
HypocalcaemiaProlongs QT interval (ST segment)
HypercalcaemiaSh t i f QT i t l (QT f T)Shortening of QT interval (QTa – apex of T)
Systematic approach to arrhythmia recognition
TachyarrhythmiasTachyarrhythmiasSupraventricularVentricular
Narrow complexWide complexWide complex
R l l / i lRegular, narrow complex/supraventricularprinciples behind the components of the algorithm
Regular narrow QRSt h ditachycardia
visible P wavesvisible P waves
atrial rate greater than i l
YesNo
ventricular rateyes no
atrial tachycardiaatrial flutter
identify RP interval
RP<PR RP>PR
RP < 70 msec RP> 70 msec atrial tachycardiaatypical AVRT/AVNRT
AVNRTAT with 1o AVB
AVNRTAVRT, AT
Systematic approach to arrhythmia recognition
Narrow complex/supraventricular (normal QRS duration, appearance)QRS l f 120 ( d l )
Cl ifi i h
QRS normal for age <120 msec (adults)
Classification schemesMechanistic
automaticity/ectopicautomaticity/ectopicreentrytriggeredgg
Anatomicalatrial, junctional, accessory pathway
AV l ti hiAV relationshipindependent, dependent
Systematic approach to arrhythmia recognition
Narrow complex/supraventricular
Combined anatomical/AV relationship
D dDependentthe arrhythmia requires both atrium and ventricleto continueto continue
Independentpthe arrhythmia continues regardless of the involvement of the other chamber
Systematic approach to arrhythmia recognition
Narrow complex/supraventricular
Direction of activationarrhythmia arises in the atriumythe atrial activity drives the ventricle
the atrium is activated by impulses that arise lowerdown (AV node, ventricle)
Sinus nodeatrial ectopic focus
Reentry circuitAtrial Flutter
P=QRS
p
AtriumP=QRSP<QRS
P=QRSP>QRS JET
Ventricle
Independent arrhythmiasCan have different rates in 2 chambersAtrium may be faster in one, may be slower in otherMore (or less) P waves than QRS complexes on ECG
AVNRT
atrium P=QRS
ventricleAVRT
ventricle
h h i d d b h h barrhythmia dependent on both chambersexpect a 1:1 relationshipone P for each QRS on ECGone P for each QRS on ECG
Systematic approach to arrhythmia recognition
Narrow complex/supraventricular
Anatomical Indep/dependentSNRT atrium independentSNRT atrium independentAtrial tach atrium independentAtrial flutter atrium independentAtrial fib atrium independentAVNRT Atr/AV node dependentAVRT Atr/Cond/vent dependentAVRT Atr/Cond/vent dependentJET AV node independent
Systematic approach to arrhythmia recognition
Locate P waveCalculate RP and PR intervals
R Rpseudo r’
P
RP/PR <1
pseudo
RP/PR <1
RP/PR>1RP=PR
RP/PR>1Long RP tachycardia
Systematic approach to arrhythmia recognition
2 explanations for same ECG
A (or P)(o )fast
slow
V (or R)1o AV block
Systematic approach to arrhythmia recognition
Regular, narrow complex tachycardia with no visible P wavesg , p y
Could be simple, uncomplicated AVNRTp p
Systematic approach to arrhythmia recognition
Concealed atrial activityadenosinecarotid sinus massage
Concealed atrial activity
Regular narrow QRSt h ditachycardia
visible P wavesvisible P waves
atrial rate greater than i l
YesNo
ventricular rateyes no
atrial tachycardiaatrial flutter
identify RP interval
RP<PR RP>PR
RP < 70 msec RP> 70 msec atrial tachycardiaatypical AVRT/AVNRT
AVNRTAT with 1o AVB
AVNRTAVRT, AT
Systematic approach to arrhythmia recognition
l h f f h h diIn general the common forms of SVT are short RP tachycardias (RP/PR<1), because the atrial activation is from rapid retrograde conduction to and then activation of the atriumconduction to, and then activation of, the atrium
Long RP tachycardias (those with a normal looking PR interval) g y ( g )are either tachycardias arising in the atrium, or unusual forms of SVT.
Sometimes it may be difficult to differentiate whether the atrium has been activated from the top or retrogradebeen activated from the top or retrograde.
Systematic approach to arrhythmia recognition
The analysis of the electrocardiogram in narrowThe analysis of the electrocardiogram in narrow complex SVT requires an understanding of the possible mechanisms, anatomical substrates and atrioventricular dependence.
Being aware of all these features will usually enable anBeing aware of all these features will usually enable an accurate diagnosis to be made on the electrocardiogram.