Electrocardiography (ECG or EKG) is the process of recording the electrical activity of the heart over time using electrodes placed on a patient's body. These electrodes detect tiny electrical changes on the skin arising from the heart muscle during each heartbeat. The ECG traces the heart's electrical activity through the various conduction pathways and different deflections in the tracing correspond to atrial and ventricular depolarization and repolarization. A normal ECG tracing shows the P wave, QRS complex and T wave and time intervals can provide information on heart rate and conduction delays.

1. Electrocardiography
PREM (2015A5PS862H)
BITS PILANI HYDERABAD CAMPUS

2. What is ECG ?
 Electrocardiography (ECG or EKG) is the process of
recording the electrical activity of the heart over a period of
time.
 Electrical activity recorded by using electrodes placed on a
patient's body.
 These electrodes detect the tiny electrical changes on the
skin that arise from the heart muscle depolarizing during
each heartbeat.

3. Normal Impulse Conduction
Senatorial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
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4. Impulse Conduction & ECG
Senatorial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
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6. The “PQRST”
 P wave – Atrial depolarisation.
 QRS – Ventricular depolarisation.
 T wave – Ventricular repolarisation.
 The PR interval - Atrial depolarisation + delay in AV junction
 The QT interval – Repolarisation of Ventricle + depolarisation
of Ventricle

7. Lead Placement
 In a conventional 12 lead ECG, ten electrodes are placed on
the patient's limbs and on the surface of the chest.
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8.  The overall magnitude of the heart's electrical potential is
then measured from twelve different angles and is recorded
over a period of time (usually 10 seconds)
 The overall magnitude and direction of the heart's electrical
depolarization is captured at each moment throughout
the cardiac cycle.
 The graph of voltage versus time produced by this medical
procedure is referred to as an electrocardiogram.

9. The ECG Paper
Horizontally
- One small box - 0.04 s
- One large box - 0.20 s
Vertically
- One large box - 0.5 mV
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10. Rate
Rule of 300- Divide 300 by the number of
boxes between each QRS = rate.
(300 / 6) = 50 bpm
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11. HR of 60-100 per minute is normal
HR > 100 = tachycardia
HR < 60 = bradycardia

12. References:
 www.google.com
 https://en.wikipedia.org/wiki/Electrocardiography
 BITS –Pilani Library
 http://www.ozemedicine.com/wiki/doku.php?id=ecg_eas
y
 https://commons.wikimedia.org/wiki/File:ECG_principle_
slow.gif