How the electrocardiogram recording from the body surface?

Answer 1

An Electrocardiogram (usually called an EKG or ECG) is simply an instrument that senses electrical activity (polarization and depolarization) and records the findings on paper.

The EKG is not recording the action of the heart, but rather it is recording the "electrical activity" of the heart.

When the heart muscle cells go through the process of contracting and relaxing, they are actually responding to electrical impulses.

This small amount of natural electrical current can be sensed by putting "leads" or sensors on key areas of the body, then using the machine to "look" at the heart from different angles, seeing how the electricity is flowing.

A simple EKG can be done only using three leads. This is how heart patients are normally monitored in the hospital, and the views that are available in this manner are limited.

Using 12 leads--including leads placed at certain spots on the chest of the patient--more "views" of the heart electrical activity are available.

Doctors look for signs that the electrical energy is being blocked, slowed down, speeded up, irregular or interrupted.

Based on which view an abnormality can be seen in, the doctor can give a fairly good diagnosis of what is happening to the heart, without ever actually seeing the heart muscle itself.

If your body were not full of water and electrolytes (sodium, potassium, calcium, chloride) the impulses would never be able to conduct to the skin, and the reading would be impossible.

I hope this helps.

G.E.T. RN
Registered Nurse (retired)

Answer 2

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