![](https://ohmaala.com/wp-content/uploads/2023/03/ECG-YAR-01-1024x462.jpg)
ECG/EKG (Electrocardiogram) Measures electrical activity of the heart to detect cardiac problems.
Lets See some important concepts about ECG from the figures below:
![](https://ohmaala.com/wp-content/uploads/2023/03/ECG-Fig-1-leads.jpg)
Figure 1. Electrode positions on an ECG (EKG).
![](https://ohmaala.com/wp-content/uploads/2023/03/ECG-Fig-2-electrical.jpg)
Figure 2. The electrical activity on an ECG (EKG).
![](https://ohmaala.com/wp-content/uploads/2023/03/ECG-Fig-3-electrical.jpg)
Figure 3. The electrical activity on an ECG (EKG).
The areas represented on the ECG are summarized below:
- V1, V2 = RV
- V3, V4 = septum
- V5, V6 = L side of the heart
- Lead I = L side of the heart
- Lead II = inferior territory
- Lead III = inferior territory
- aVF = inferior territory (remember ‘F’ for ‘feet’)
- aVL = L side of the heart
- aVR = R side of the heart
![](https://ohmaala.com/wp-content/uploads/2023/03/R-27.jpg)
Figure 4. The segments of the ECG.
What do the segments of the ECG represent?
- P-wave: Atrial contraction
- PR interval: Represents the time taken for excitation to spread from the sino-atrial (SA) node across the atrium and down to the ventricular muscle via the bundle of His.
- QRS: Ventricular contraction
- ST segment: Ventricular relaxation
- T-wave: Ventricular repolarisation
Normal duration of ECG segments:
- PR interval: 0.12 – 0.2 secs (3-5 small squares)
- QRS: <0.12 secs (3 small squares)
- QTc: 0.38 – 0.42 secs
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