Electrocardiography

Electrocardiography Prof. K. Sivapalan

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. ECG

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. ECG

Electrocardiograph. ECG

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. ECG

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 aVR aVL Lead III Lead II aVF ECG

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. ECG

Information from ECG. • Rate. • Rhythm • Pattern of spread of impulse and integrity of conducting system. • Size [thickness] of myocardium. • Electrolyte imbalance. • Damage to myocardium. ECG

Examples of abnormal ECG. SA node block ECG

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. ECG

Electrocardiography