Electrocardiography is a technique for graphing the electrical activity of the heart using electrodes attached to various locations of the body. This graph is known as the ECG.

The standard practice presently is to put 10 electrodes in the following 10 different locations on the body to produce an electrocardiogram: 4 Limbs (Right Arm, Left Arm, Left Leg, and Right Leg) plus 6 on the chest around the heart in precise areas. The Wilson’s central terminal is used to detect the voltage difference/potential between two electrodes or a shared virtual electrode.

The average potential measurements between three of the limb electrodes – Right arm, left arm, and Left Leg – make up Wilson’s central terminal. “Leads” refers to voltage difference measurements.

How many leads are required for ECG Graph?

To complete the ECG graph, 12 ‘leads’ are required. Three limb leads, three augmented limb leads, and six chest leads are among the 12 leads (also called precordial leads). The augmented limb leads and chest leads (also known as precordial leads) monitor the voltage difference/potential between the limb and chest electrodes vs. the virtual electrode, whereas the three limb leads assess the voltage difference/potential between the limb electrodes.

People frequently use the term “lead” to refer to electrodes as well, leading to confusion about whether ECG equipment has 10 or 12 leads.

When a patient’s heart activity needs to be observed for a longer time, ECG variants with fewer electrodes, such as 3-electrodes or 5-electrodes, are utilized to help mobility. These are sometimes referred to as 3-lead / 5-lead ECGs, but the numbers 3 & 5 refer to the number of electrodes used, not the number of leads available. The 3 and 5-electrode ECGs collect less information than the 12-lead ECGs.

The 3-electrode ECGs only capture the limb-leads and do not provide an anterior view, making them ideal for rhythm monitoring. In a 5-electrode ECG, all six limb leads are recorded, as well as one chest view. When someone refers to a 5-channel ECG or a 5-lead ECG, they are referring to a 5-electrode ECG. 

What is a channel in ECG?

The term ‘channels’ is also widely used to refer to the number of channels on ECG equipment. Single-channel, 3-channel, 6-channel, and 12-channel ECG machines are available. Each of the above-mentioned lead measurements is then recorded after passing through an ‘amplifier’ channel. Each lead is recorded and presented one at a time in a single-channel system. The ECG contains a microprocessor in a multi-channel system that regulates signal processing dependent on the number of channels.

The signals are amplified, filtered, and then transferred to a multiplexer for processing. The multiplexer accepts all inputs, reconstructs signals, de-multiplexes, and outputs to the display screen or chart recorder. If it’s a 3-channel ECG, the microprocessor divides the 12-lead signals into four groups of three and analyzes them. Similarly, with a 6-channel device, the same 12-leads are processed in two groups, whereas in a 12-channel device, the same 12-leads are processed concurrently. As a result, the bigger the number of channels, the faster the ECG recording. ‘Channels’ is distinct from ‘electrodes’ or ‘leads.’

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