electrocardiogram (ecg) cardiovascular system (cvs 227) basic prinicples dr.mohammed sharique ahmed...
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CONDUCTION SYSTEM OF THE HEART 3TRANSCRIPT
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ELECTROCARDIOGRAM (ECG)Cardiovascular System (CVS 227)
BASIC PRINICPLESDr.Mohammed Sharique Ahmed Quadri
Asst. professor in physiologyAl Maarefa College
الرحيم الرحمن الله بسم
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CONDUCTION SYSTEM OF THE HEART
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PRINCIPLE OF RECORDING ECGBattery
The body is a good conductor of electricity
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ELECTROCARDIOGRAM Electrocardiogram:
Measure of the electrical activity of the heart per unit time.
Potential differences generated by heart are conducted to body surface where they can be recorded on electrodes on the skin.
Does NOT measure the flow of blood through the heart.
Electrocardiograph : device that records the electrical activity of the heart
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ECG What is Lead? ECG recorded on the paper after
putting the electrode.
What is Electrode? It is a metallic plate which conducts
electricity.
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LEADS ARE LIKE PICTURES OF THE HEART
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STANDARD 12-LEAD ELECTROCARDIOGRAM Six Limb Leads :
Three Bipolar Limb Leads( standard limb leads) Frontal plane currents (right, left, inferior, superior) named as , I, II , III
Three Unipolar Limb Leads ( augmented limb leads)
named as aVR, aVL, aVF
Six precordial leads Horizontal plane (anterior, posterior, right and
left forces)8
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BIPOLAR / STANDARD LIMB LEADS Record the electrical potential
difference in the frontal plane In bipolar lead, we record potential
difference between two active electrodes.
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UNIPOLAR (AUGMENTED) LEADS Record electrical potential in the frontal
plane In Unipolar lead, we record potential
difference between active electrode and other electrode at zero potential.
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EINTHOVEN’S TRIANGLE The axis of the limb
leads form an equilateral triangle around the heart’s
electrical field
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PRECORDIAL (CHEST) LEADS
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HEART IN THREE DIMENSION
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ELECTRODES & WAVES
If current is flowing towards the recording electrode, we get upward deflection.
If current is flowing away from the recording electrode, we get downward deflection.
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Standard 12 Lead ECG
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THE ECG PAPER Horizontally
One small box - 0.04 s One large box - 0.20 s
Vertically One large box - 0.5 mV
1mm
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BASIC COMPONENTS Waves
Segments & intervals
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BASIC COMPONENTS
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NORMAL IMPULSE CONDUCTION
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers19
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IMPULSE CONDUCTION & THE ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
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THE “PQRST”
• T wave - Ventricular Repolarization
• QRS - Ventricular
Depolarization
• P wave - Atrial Depolarization
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THE PR INTERVAL
Atrial depolarization +
delay in AV junction (AV node/Bundle of His) (delay allows time
for the atria to contract before the ventricles contract)
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SEGMENTS & INTERVALS
PR interval: 0.12 – 0.20 sec QRS interval : 0.08 – 0.10sec QT interval : 0.40-0.43sec ST interval :0.32 - sec
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THE ELCTRICAL AXIS OF THE HEART Vector is diagrammatic way to show
strength & direction of impulse
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MEAN ELECTRICAL AXIS Is some total of all
vectors generated by the action potential of individual ventricular myocytes.
we measure the way the vectors looks as it travels under each of various electrode
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MEAN ELECTRICAL AXIS OF THE HEART:QRS AXIS Normal range
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Determination of Mean Electrical Axis
The QRS axis is determined by overlying a circle, in the frontal plane. By convention, the degrees of the circle are as shown.
The normal QRS axis lies between -30o and +110o.
0o
30o
-30o
60o
-60o-90o
-120o
90o 120o
150o
180o
-150o
A QRS axis that falls between -30o and -90o is abnormal and called left axis deviation.
A QRS axis that falls between +110o and +180o is abnormal and called right axis deviation.
A QRS axis that falls between +180o and -90o is abnormal and called Indeterminant (extende rt axis ) .
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REFERENCES Text book of medical physiology by
GUYTON & HALL 11th edition
Text book physiology by GANONG
The ECG made Easy by John R.Hampton sixth edition
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