The essential components of an ECG

Hyderabad: This article is in continuation of the previous articles that help you understand what constitutes the biological sciences and its varied branches/ concepts. Today, we would be discussing the fourth part of the Biomedical technology with a focus on Electrocardiogram (ECG). A normal ECG consists of i. Waves ii. Intervals iii. Segments iv. Complexes […]

Hyderabad: This article is in continuation of the previous articles that help you understand what constitutes the biological sciences and its varied branches/ concepts. Today, we would be discussing the fourth part of the Biomedical technology with a focus on Electrocardiogram (ECG).

A normal ECG consists of
i. Waves

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ii. Intervals

iii. Segments

iv. Complexes

Waves:

* The waves in a normal record are named P,Q,R,S & T in that order
* A typical ECG tracing of a normal heart beat (or cardiac cycle) consists of
a. ‘P’ wave
b. ‘QRS Complex’ of waves
c. ‘T’ wave
‘P’ Wave:
* It represents the atrial depolarisation/atrial systole.

* ‘P’ wave shows that the impulse is passing through the atria.
* The normal duration of a ‘P’ wave is – 0.1 sec

‘QRS Complex’ of waves:

* ‘Q’ wave is a small negative wave.
* ‘R’ wave is a tall positive wave.
* ‘S’ wave is a negative wave.
* The normal duration of QRS complex of waves is about 0.08-0.1 sec.
‘T’ wave:
* ‘T’ wave is a positive.

* It represents the ventricular repolarisation.

* Its duration is 0.2 sec.
Intervals:
a. P-R interval is the interval between the onset of ‘P’ wave and the onset of Q wave.

* P-R interval is normally 0.12-0.2 sec.

b. Q-T Interval is the interval between the onset of ‘Q’ wave and the end of the ‘T’ wave.

* It represents the electrical activity in the muscle of the ventricles (Ventricular depolarisation).

* QT interval is dependent on the heart rate (faster the heart rate, shorter the interval).

* It lasts for about 0.4 sec.

c. R-R interval signifies the duration of one cardiac cycle and it lasts for about 0.8 sec (60/70=0.8 sec)

Segments:

* S-T segment is the time period between the end of the ‘S’ wave and the onset of the ‘T’ wave.
* It is an isoelectric /zero voltage period
Clinical inference from ECG:
* Enlarged ‘P’ wave indicates enlarged atria.

* Variations in the duration, amplitude and morphology of the ‘QRS complex’ indicate disorders such as bundle branch block (block of conduction of impulses through the branches of bundle of his).

* If the duration of the P-R Interval is prolonged, it indicates delay in conduction of impulses from S-A node (pacemaker) to the A-V node.

* P-R interval is prolonged in Bradycardia (slow beating of the heart) and shortened in Tachycardia (fast beating of the heart).

* Prolonged Q-T interval indicates myocardial infarction (MI) and hypothyroidism. Shortened Q-T interval indicates Hypercalcemia.

* Elevated S-T segment indicates myocardial infarction.
* Tall ‘T’wave indicates hyperkalemia, small, flat or inverted ‘T’ wave indicates hypokalemia.

By Dr. Modala Mallesh
Subject Expert

Palem, Nakrekal, Nalgonda

9989535675