ECG - How to read?

ECG is a cardiac test performed to check the condition of the heart. It gives information about certain diseases that may need immediate treatment. This is an important topic for biology class 12.

ECG - Full Form

The full form of ECG is electrocardiogram. A graphic record or representation of the electrical events that occur during a heart beat is known as electrocardiogram or ECG. Einthoven is known as the father of electrocardiography.

ECG Test

What is ECG test? It is a frequently asked question. Electrocardiography is done with the help of a machine called electrocardiograph. In this process, leads are fixed on two arms, chest and left leg after applying a jelly which improves the conduction of electricity. The electrocardiograph detects and amplifies the electric current of the heart. A wavy line is drawn by the recording pen after the transmission of this electric current. It represents the deflection waves.This record is known as the electrocardiogram or ECG. A change is produced in the electric potential across the membrane of the cardiac muscle fibres by the cardiac impulse of the heart muscles. The body fluids and tissues are good conductors of electricity. So the electric changes that take place in the heart muscles are recorded on the electrocardiograph.

ECG - How to read?

There occurs five waves in the ECG tracing. These are P wave, QRS complex which consists of Q, R and S waves and T wave. These waves are of two types -

1.Positive Waves - P, R and T waves are known as the positive waves. These three waves are present above the baseline of the ECG.

2.Negative Waves - Q and S waves are known as the negative waves. These two waves are present below the baseline of the ECG.

The sharp waves in electrocardiograph are Q, R and S while the waves that appear blunt are P and T waves. Interval is the part of baseline which is found between any two deflections.

An impulse of contraction that sweeps over the atria causes the P wave.It is formed by the activation of SA node. The contraction of atria is represented by the PQ interval. Its duration is 0.16 second. The impulse of contraction that spreads from the AV node through the bundle of His, branches of bundle and purkinje fibres and the contraction of the ventricular muscles is indicated by the QRS wave. The relaxation of the ventricular muscles is represented by the T wave. The duration of the waves QRST is 0.3 seconds. The changes in the pattern of electrical potentials recorded in ECG represents the defects in cardiac structures and functions.

For example - At the time of atherosclerosis heart disease and rheumatic fever, there occurs the inflammation of AV node and atria. Due to this the length of PQ or PR interval increases.Unusual ratios of S and R waves points towards the enlargement of one side of the heart. Large sized Q and R waves indicates heart attack. The failure of conduction of impulse in the purkinje system causes prolonged QRS complex.The time gap between the termination of spread of impulse through ventricles and its repolarization is shown by the S-T interval. If the heart muscles don't receive sufficient oxygen, the S-T segment appears to be raised. If a heart muscle is damaged the S-T segment is depressed. T wave represents the ventricular repolarization. The T wave is flattened if the heart muscles receive insufficient oxygen.

Hope this article ECG-How to read? for notes of biology class 12 would be helpful to you. You may also find Worksheets for Science to practice this topic. Please comment if you want articles on any topic.

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