Download VECTORIAL ANALYSIS OF ECG

VECTORIAL ANALYSIS OF ECG
LEARNING OBJECTIVES
At the end of the lecture student should
1. Understand about vector and the principles apllied in plotting electrical vector of heart
2. Understand the relationship between vectors generated in the heart and EKG waves
3. Be able to assign appropriate vectors to depolarizing and repolarizing signals at different
angles to the recording electrodes
4. Understand the concepts of instantaneous vectors and net vectors
5. Be able to dissect a vector loop into component instantaneous vectors
6. Be able to reconstruct a vector loop from individual traces
7. Understand how the hexaxial reference system is generated and be able to identify the
individual axes
At the end of the lecture the student should be able to know :
About the rate of ecg tracing
About how to calculate the rate from ECG tracing
About ruleof 300
About sinus rhythm
About sinus brady and tachycardia
About overdrive supression
INTRODUCTION TO VECTOR
 During each cardiac cycle current flows in a particular direction
 The heart is a functional syncytium
 Depolarization (or repolarization) of one cell will depolarize (or repolarize)
adjacent cells
 Many dipoles will be formed
 The electrical fields generated by summating dipoles are represented by
vectors
 Any change in the direction of impulse transmission causes the abnormal
electrical potentials around the heart which alters the shapes of waves in
the ECG
THEORETICAL CONCEPTS OF VECTOR ANALYSIS
 A wave of depolarization or repolarization moving
 Towards the positive electrode of a lead will cause a positive (upward)
deflection
 away from the positive electrode of a lead will cause a negative
(downward) deflection
 perpendicular to a lead will cause no net
deflection.
AXIS OF LIMB LEADS
 Each lead have two electrodes
 direction from –ve to +ve electrode is called
axis of the lead
 Axis of lead 1 is zero (0) degree because
electrode lies in the horizontal direction with +ve to left
side (left arm)
 Axis of lead
 II is---- +60 degree
 III---- +120 degree
 aVR---- +210 degree
 aVL---- -30 degree
 aVF----- +90 degree
EINTHOVEIN’S TRIANGLE
 Triangle around the area of heard
 Apices represent the positive electrodesof bipolar
limb leads
Einthovein’s law:
Sum of voltage in any 2 leads is equal to voltage in 3rd
lead
HEXAXIAL GRID
 To work with vectors in the frontal plane, a
combination of the three standard limb leads and the
three augmented limb leads is often used
 The common way to represent this is as a hexaxial
grid
 Hexaxial = 6 axes, 1 for each lead
VECTOR
 Arrow that shows the direction of electrical potentials generated by elect
flow
 Arrowhead in the positive direction
 Length proportional to voltage of potential
 Direction of vector is denoted in degrees e g. When
vector is horizontal and is directed to left side the vector is said to extend in
the direction of 0 degree
 When extends straight down wards it is equal to 90 degrees
MEAN QRS VECTOR
 Normally direction of vector during spread of depolarization wave through
ventricle called QRS vector is about +59 degree
VECTOR ANALYSIS OF POTENTIALS RECORDED IN DIFFERENT LEADS
 When we use vector and axis together we will be able to determine the
potentials recorded in ECG of each lead
 If we know the direction and amplitude of instantaneous mean vector of
heart, by using axis of limb leads we can draw vectors and know about
potential and direction of deflection in each limb lead
VECTOR ANALYSIS - FROM THEORY TO APPLICATION:
Determining the Mean QRS Axis from EKG Traces
 Most often used to determine the direction of depolarization (or
repolarization) of the atria and ventricles
 Most common use of vector analysis is to determine the mean axis of
depolarization of the ventricles
 Referred to by several additional names (mean QRS axis, or often simply
mean axis)
 By determining the mean axis of ventricular depolarization information is
obtained about the conduction pathway, anatomical abnormalities.
Stepwise Determination of Mean Axis Using the Triaxial Method Using the
following tracing
STEP 3
•Draw perpendiculars from the apices of
two net vectors of two lead
STEP 4
•The point of intersection of these two
perpendicular line represent the apex of
mean QRS vector
•The point of intersection of lead I and
III axes represent the negative end of
mean QRS vector
•Mean QRS vector is drawn
•The length determines the magnitude
of average potential generated by
ventricles during depolarization
•Direction represent mean electrical
axis
cALCULATING AXIS FROM LEAD I AND
aVF
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Using Lead I and AVF:
Lead I: +10 mm
AVF: +16.5 mm
Use 2 divisions per mm to keep
vector arrows on scale.
 Draw perpendiculars from heads
of arrows.
 Draw head of mean arrow at
intersection of perpendiculars.
 the use of AVF and Standard
Limb Lead I is a common shortcut
CAUSES OF AXIS DEVIATION
Common Causes of Left
Axis Deviation:
a. Left ventricular
hypertrophy.
b. Pregnancy.
c. Obesity.
d. Infarct in right ventricle.
Common Causes of Right
Axis Deviation:
a. Right ventricular
hypertrophy.
b. Infarct in left ventricle.
c. Slight right axis deviation may be normal for children and very tall, thin
adults.
VECTOR ANALYSIS OF THE WAVE OF DEPOLARIZATION IN THE VENTRICLES
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At time zero (T0),before depolarization starts,
the ventricles are completely polarized
the cells are all at their resting membrane potential
no voltage differences between points
there is no vector at this time.
At T1
the septum begins to depolarize from the patient’s left to right.
the sum of all the electrical activity in the ventricles can berepresented by a
short vector, oriented as indicated.
 VECTOR ANALYSIS OF THE WAVE OF DEPOLARIZATION IN THE VENTRICLES
 At T2
 the septum, the apex, most of the right ventricle, and part of the left
ventricle are depolarized
 magnitude of the vector is large
 directed along the axis of the heart from base to apex
 At T3
 the sum of the electrical activity is directed towards the left
 smaller in magnitude than at T2.
 Except for posterior basilar portion of the ventricle, all ventricle is
depolarized at this time.
 VECTOR ANALYSIS OF THE WAVE OF DEPOLARIZATION IN THE VENTRICLES
 At T4
 the remaining portion of the ventricle depolarizes.
 represented by a small vector directed towards the base of the left
ventricle
 At T5
 the ventricles are completely depolarized
 there is no voltage difference between different locations
 no vector.
VECTORCARDIOGRAM
 The sum of the instantaneous vectors leads
to the waveforms we record as an
vectorcardiogram
RATE AND RHYTHM OF ECG
RATE
REVISION OF ECG PAPER CALIBRATION
 1 inch = 1 second
 Each inch is divided by dark black
lines into 5 big square
 Each big square= 1/5=0.2 sec
 Each big square is further divided
into 5 small square
 1 small square = 0.2/5= 0.04 sec
 1smallsquare = 0.04 sec =1mm
 1 second =25 smallsquare
 60second =1min =25 X 60=1500 small square =300 big square
DETERMINING THE HEART RATE
RULE OF 300
 Take the number of “big boxes” between
neighboring QRS complexes
 divide this into 300
 The result will be approximately equal to the rate
 this method only works for regular rhythms.
# of big
boxes
Rate
1
300
2
150
3
100
4
75
5
60
6
50
RYTHM
SINUS RYTHM
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Normal rhythm of heart
Cardiac impulse originated in SA node, atria depolarize
Represented by P wave
Travel down to AV node
AV nodal delay
Represented by PR interval
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Impulse travel down to purkinje fibers
Ventricles depolarize
Represented by QRS complex
Then repolarize
Represented by T wave
Again SA node send another impulse and cycle repeats
Sinus node discharge these impulse at a pace of 60-100/min
SINUS RYTHM
 Rhythm that originated
by SA node
 on ecg, P wave
followed by QRS
complex
 QRS complex followed
by P wave
 @ 60-100 impulses per
min
SINUS BRADYCARDIA
 Sinus rhythm
 Originated in SA
node
 P wave followedby
QRS complex
 Rate slower than 60/ min
SINUS TACHYCARDIA
 Sinus rhythm
 Originated in SA node
 P wave followed by QRS complex
 Rate more than 100/min
SINUS ARRYTHMIA
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Normal physiological mechanism
Minimal variation in pace of SA node with respiration
Minimal increase in heart rate with inspiration
Inspiration- activated sympathetic stimulation of SA node
Minimal decrease in heart rate with expiration
Expiration –activated parasympathetic stimulation of SA node
AUTOMATICITY FOCI
 Potential pace makers in heart that have the ability to pace whenever SA
node fails to do so
 Pace at their own inherent rate
Atrial automaticity foci
 in atrial conductionsystem
 Rate is 60 – 80 /min
Junctional automaticity foci
 Middle and distal portion of AV node
 @40-60 beats/min
Ventricular automaticity foci
 In bundleof Hisand bundlebranches
 paces@ 40 – 20beats/min
OVERDRIVE SUPPRESSION
 Heart’s fail safe pacing mechanism
 Functional characteristic of all automaticity foci
 Rapid pace making activity suppresses any other slower pace making
activity
 Normally SA node has the highest
pacing rate--- overdrive suppress
all other foci
 If one focus fail the next in line ,
no longer over suppressed and
become the pace maker overdrive-suppressing all other foci
REFERENCES
Guyton and Hall text book of physiology
THANKS