An ECG is a graphic recording of the electrical activity of the heart over time captured by electrodes placed on the skin. It detects the impulse as it travels through the heart and provides information about heart rate and rhythm, as well as the size and position of the chambers, any damage to the heart, and the effects of drugs or devices. The standard ECG uses 12 leads attached at specific positions on the limbs and chest to detect the P, QRS, and T waves representing atrial depolarization, ventricular depolarization, and ventricular repolarization respectively. The ECG is useful for diagnosing heart conditions like heart attacks, arrhythmias, and damage as well as monitoring effects of drugs.

1. ECG / ELECTROCARDIOGRAM /
ELECTROCARDIOGRAPH/ EKG

2. DEFINITION
• ECG Is a graphic representation of
electrical activity produced by heart beat.
• The electrical activity spreads from heart
to the body surface from where it is
amplified by ECG machine and can be
graphically recorded.

3. Parts of an ECG
• 1) ECG Machine
• 2) Electrodes- The standard ECG has 12
leads.
– a) 6 leads are “limb leads”
– b) 6 leads are “precordial leads”

4. • A) 6 leads are “limb leads”
– The six limb leads are called lead I, II, III, aVL,
aVR and aVF.
– The letter “a” stands for “augmented".

5. • B) 6 leads are “precordial leads”
• The six precordial leads are called leads V1, V2, V3, V4,
V5 and V6

6. • V1- In the fourth intercostal space (between
ribs 4 and 5) just to the right of the sternum
(breastbone)
• V2- In the fourth intercostal space (between
ribs 4 and 5) just to the left of the sternum.
• V3- Between leads V2 and V4.
• V4- In the fifth intercostal space (between ribs
5 and 6) in the mid-clavicular line.
• V5- Horizontally even with V4, in the left
anterior axillary line.
• V6- Horizontally even with V4 and V5 in the
mid-axillary

8. • P-wave:
– It is a small upward wave that appears first.
– It indicates atrial depolarization (systole), during
which excitation spreads from SA node to all over
atrium.
• QRS wave:
– It represents the ventricular depolarization
(systole)Just after QRS wave begins, ventricles
starts to contracts.
– Hence QRS wave represents ventricular systole
• T- wave:
– It is third small wave in the form of a dome-shaped
upward deflection.
– It indicates ventricular repolarization (diastole)

10. • P-R interval:
–It represents the time required for an
impulse to travel through the atria, AV
node and Bundle of His to reach
ventricles.
• S-T segment:
–It is measured from the end of S to the
beginning of T- wave
–It represents the time when ventricular
fibers are fully depolarized

11. USES OF ECG
• 1) Diagnosis of heart disease like Ischemic
heart disease, Myocardial infarction
• 2) Hypertrophy of atria and ventricles
• 3) Electrolyte imbalance like potassium
cause T wave depression