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

In our last article, we talked about the passage of electrons along a metal wire, or lead. It is not enough to pass the electrons along a lead; they must be passed along with little or no interference. It the physical nature of the lead that will determine the fidelity of the signal that reaches the EKG machine. The wrong choice of material, even if it is a metallic substance, can make the EKG useless. It would be like trying to make an EKG lead out of a piece of twine.

Metal has resistance, and it is that resistance that can transform the electricity into other energy forms, heat for example, and alter the output on the other end.

Think of it this way: we are not talking about wires, but tubes. And the tubes are carrying water, as tubes are wont to do. Let the water be analogous to the electricity. If there is a tube filled with wax, there would be no water coming through. This is a twine based EKG lead, a non-conductive lead. Its use is so limited as to be absurd.

But what about something not so outlandish, a metal lead, but a high resistance metal. Our tube is now filled with rocks, but they are sharp, jagged rocks. Water passes through, but does so slowly and the water that comes out the other end is turbulent and filled with bubbles. This is better than our non-conductor, but the electricity is too different from the input to be of any use in an EKG.

What we need is a tube that is as good a conductor as we can find. The best would be a tube with no filling. But that, extending our metaphor, is superconductivity. And that currently cannot occur at room temperature. Super cooling the patient to minus 423 degrees Fahrenheit, which is the necessary range for superconductivity, would give negative clinical outcomes to an EKG, not to mention increasing the price.

What is used, and functions well, are good conductors. Aluminum, copper and in some instances silver or gold are good choices. Going back to the tube analogy; these are tubes filled with smooth rocks, the water (electricity) will pass through with little turbulence and come out the other end will some, but not many, bubbles.

So, the signal has gone from the heart to the EKG machine, but there is one last part that must be played. The signal must be loud enough to be interpreted.