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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

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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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