Electrocardiography

Prof. K. Sivapalan

2013 ECG 2

Principle of Electrocardiogram.

• Trunk as volume conductor.• Positively charged and

negatively charged areas create electrical field.

• The field changes during spread of impulse.

• Depolarization towards – upward deflection & away – downward deflection.

2013 ECG 3

Einthovens triangle.• When the source of the

electrical field is at the centre of an equilateral triangle, the sum of electrical potential at the three angles is zero.

• Since the heart is roughly at the centre of the triangle and the source moves, 5000 ohm resistance is added to the three leads to get zero potential.

2013 ECG 4

Electrocardiograph.

2013 ECG 5

Electrocardiograph.

2013 ECG 6

Electrocardiograph.

2013 ECG 7

Electrocardiograph.

2013 ECG 8

Electrocardiogram.

• Electrocardiogram is the record of the changes in the electrical field in the body produced by the electrical activity of the heart.

• It represents the sequence and strength of the electrical events in the heart.

2013 ECG 9

Recording ECG.

Coronal plane:• Limb leads [Bipolar

leads].• Augmented limb

leads.[unipolar]

Transverse plane:• Chest [Unipolar] leads

V1 to V6 across the chest.

Lead I

Lead II Lead III

aVR aVL

aVF

2013 ECG 10

Typical Electrocardiogram.

• Paper speed- 25 mm/sec.• Vertically, 1 mV = 10 mm.• P wave – first wave.• Q wave – first down.• R wave – first up in QRS.• S wave – down after R.• T wave – after QRS.• U wave – after T.• PR interval – 0.18 sec.• QRS duration – 0.08 sec.

2013 ECG 11

Information from ECG.

• Rate.• Rhythm• Pattern of spread of impulse and integrity of conducting

system.• Size [thickness] of myocardium.• Electrolyte imbalance.• Damage to myocardium.

2013 ECG 12

Examples of abnormal ECG.

SA node block

2013 ECG 13

Examples of abnormal ECG.Normal.

K+ – 4 – 5.5 meq / L

K+ – 7 meq / L.

K+ – 8.5 meq / L

K+ – 3.5 meq /L.

K+ – 2.5 meq / L.