Download Initiation and Spread of Electrical Activation in the Heart

ELECTROCARDIOGRAPHY
Ulkumen Rodoplu, MD
EuSEM
Plan
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A Normal ECG
Basic ECG Waveform
Initiation of Spread of
Electrical Activation in the
Hearth
The Magnitude and
Direction of the Activation
Process
Activation Vectors
Introduction
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Essential tool in the
investigation of heart disease.
No cardiological assessment is
complete without a 12-lead
ECG.
One hundred million ECGs are
recorded worldwide each year.
History
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19th century. The heart generated electricity.
Augustus Waller, working in St Mary's Hospital in
London: The first systematical approach about the heart
from an electrical point-of-view.
Willem Einthoven, working in Leiden, The Netherlands,
invented the string galvanometer, which was much more
precise than the capillary galvanometer that Waller used.
Einthoven assigned the letters P, Q, R, S and T to the
various deflections, and described the
electrocardiographic features of a number of
cardiovascular disorders. He was awarded 1924 Nobel
Prize for Physiology and Medicine for his discovery.
Initiation and Spread of Electrical
Activation in the Heart
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In normal circumstances the
whole process begins in the
sino-atrial node.
Initiation and Spread of Electrical
Activation in the Heart
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SA Node normally
initiates activation of the
atrial myocardium
AV Node transmits
activation received from
the SA Node to the
common bundle
HIS Bundle forms the
electrical connection
between the atria and the
ventricles
Initiation and Spread of Electrical
Activation in the Heart
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The right and left
bundle branches run
below the endocardial
surfaces of their
respective ventricles
The Purkinje network
spreads over the
endocardial surfaces
of the ventricles
The Basic ECG Waveform
P wave - spread of
electrical activation
through the atrial
myocardium.
QRS Complex – spread
of electrical activation
through ventricular
myocardium.
T wave – electrical
recovery of the
ventricular myocardium.
Electrical Activity & ECG
P Wave
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< 0.10 sec. wide
< 2.5 mm. amplitude
(+)……DI, II, aVF
(+) (-)… aVL
(-)… aVR
VI , biphasic or (-)
PR interval
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0.12 – 0.20 sec
QRS
Depolarisation of
ventricles
 < 0.10 sec. wide
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T Wave
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Repolarisation of
ventricles
0.12-0.25 sec. wide
(+)…DI, II, V2-6
(+) (-)…aVL, aVF
(-)….aVR
Calculation of Rate
Activation Vectors
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A vector is simply something
which has magnitude and direction.
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Direction in which the arrow points
represents the direction of the
vector.
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Length of the arrow represents the
magnitude of the vector.
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The apparent magnitude of the
activation wave will depend on the
direction from which it is sensed.
Polarisation and
Depolarisation
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Activation is actually the process of
depolarisation and the spontaneous
spread of this process over the
myocardial cells.
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Resting, healthy mycardial cells are
polarised.
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The surface membrane of each cell
has an accumulation of charges –
positive ones on the outside and an
equal number of negative ones on the
inside.
The QRS Complex
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The central oblong is the
myocardial strip.
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The arrow shows the
depolarisation vector in
magnitude and in direction.
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The deflection recorded by
each lead is shown at the side
of that lead.
A Normal 12 - Lead
Electrocardiogram
ECG Derivations
Bipolar…DI, DII,DIII
 Unipolar…aVR, aVL, aVF
 Precordial….V1….V6
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Precordial Electrodes
Einthoven Triangle
A Normal Vectorcardiogram
Electrical Axis
Electrical Axis-Triaxial Method
Electrical Axis- Hexaxial Method
Electrical Axis-Practical Method
I,II,III,aVF.. QRS(+).... Normal
 I…QRS(-), aVR…QRS(+)…RAD
 II,III,aVF.. QRS(-)....30º LAD
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Normal ECG Leads
Normal Sinus Rhytm
Sinus Tachycardia
Sinus Bradycardia
Sinus Arrhytmia
Atrial Escape Beat
Nodal Escape Beats
Nodal Rhythm in Complete AV
Block
Atrial Tachycardia
Supraventricular Tachycardia
Atrial Flutter – atrial rate 300
Atrial Flutter – 2:1 Conduction,
Atrial rate 300
Ventricular Premature Contractions
Multiform VPBs
Ventricular Couplets
Ventricular Flutter
Ventricular Fibrilation
First degree AV Block
Second degree AV Block
Wenckebach or Mobitz Type I
Second degree AV Block
Mobitz Type II