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CARDIOVASCULAR SYSTEM ELECTROCARDIOGRAM (E.C.G.)
LECTURE - 5 DR. ZAHOOR ALI SHAIKH
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It is recording of Electrical activity of the Heart by putting Electrodes on the surface of the body.
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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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ECG Machine
Electrode
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Bipolar Limb leads
Unipolar Limb Leads
Unipolar chest leads
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ECG
In bipolar lead, we record potential difference between two active electrodes.
In Unipolar lead, we record potential difference between active electrode and other electrode at zero potential.
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. 11
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Heart Rate Calculation= 1500 ÷ No. of small squares between R-R waves
Or= 300 ÷ No. of big squares between R-R waves
The Waves & Intervals
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P wave Atrial DepolarizationDuring 0.12 secVoltage (Height) 1-3mm
QRS Complex Ventricular DepolarizationTime 0.08 – 0.1 secVoltage 10mm (1mV)
T wave Ventricular Repolarization Height 2-3mm
U wave Repolarization of Papillary Muscles
PR interval Conduction time from SA node to Ventricular muscle through AV node. It measures the time from beginning of P wave to beginning of Q wave. Time 0.12 – 0.2 sec.
QT Interval Ventricular Depolarization or Repolarization Time 0.35 – 0.43 sec
REMEMBER IMPORTANT NORMAL VALUES
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P wave - 0.12 secQRS - 0.1 secPR Interval - 0.2 secQT Interval - 0.4 sec
ELECTRICAL AXIS
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1st Degree Heart Block
ST Elevation – Myocardial Infarction
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WHAT YOU SHOULD KNOW FROM THIS LECTURE?
1. P wave ---- Atrial depolarization.2. QRS complex ---- Ventricular depolarization..3. T wave ---- Ventricular Repolarization. 4. P – R interval ---- conduction time from S-A node
to ventricular muscle through A-V node time =0.12 – 0.2sec.
5. ↑PR interval more than 0.2 sec.---- Ist degree heart block.
6. Q – T interval ---- Ventricular depolarization + ventricular repolarization time =0.35 – 0.43sec.
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7. ↑QT interval ---- hypocalcemia.
8. U wave ---- repolarization of papillary muscle.
9. Prominent U wave ---- hypokalemia.
10. Prominent T wave ---- hyperkalemia.
11. Heart rate calculation
12. Sinus tachycardia
13. Sinus bradycardia
14. Sinus arrhythmia (↑ heart rate during inspiration)
15. Cardiac axis • by looking at ECG lead I & III
• By plotting 29
16. Normal cardiac axis 0o to + 90o
(-30o to + 110o )
17. You should know about Left axis deviation & right axis deviation.
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THANK YOU
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