Read about the latest news on ECG / EKG Machines

This article in the three-part series on EKG electrodes discussed the electronics of EKG electrodes. Be sure to read the other parts regarding chemistry and physics.

In the first two installments in this series, we discussed how the electrical signal of the heart is picked up by the lead and reaches the machine. Now that the signal from the heart has arrived at the EKG machine, there is still one problem to solve. The electric signal from the heart is still small, so small in fact that it would be hard to detect, much less interpret. And it is, after all, the interpretation that is the most important thing.

Today, there is a computer that assists with the final product. But even in the early days of EKG machine, the signals alone were too small to see enough variation to be clinically relevant. There had to be a solution, and that solution was found with electronics.

Electronic signals of all types are waves. Even a small signal is in wave form. If this signal is passed though a device called an amplifier, power is taken from another source and added to the small signal. The shape of the wave is maintained, but the power and size of the wave made larger. It is like setting the enlargement button on a copy machine.

This is the basis of musical amplifiers. The signal strength can be varied according to the needs and wishes of the performers. But on an EKG machine, there is no reason to vary the signal across a range. No one sets EKG machines to eleven, or anywhere else for that matter. There needs to be a constant amplification. This is done with a type of amplifier called a differential amplifier. It multiplies the difference between the input signal and the expected output by a set factor. The accuracy of these factors can be increased by adding additional circuits with additional factors wired in. An appropriate layer of the circuits gives a very high level of accuracy, with little variation or interference that would negatively affect the output of an EKG machine.

These multi-circuit differential amplifiers are called instrument amplifiers. In addition to all these circuits, there are buffers which eliminate the need for so much additional power to match the input wave. It is as these buffers clean up the signal before the additional circuits take over. This increases the overall accuracy of the signal and ultimately the accuracy of the EKG machine, allowing it to produce a tracing that can then be used to diagnose electrical problems in the heart.