thaler chapter 1

Making Waves

33

Making Waves

Electrodes can be placed anywhere on the surface of the body to record the heart’s electrical activity. If we do this, we quickly discover that the waves recorded by a positive electrode on the left arm look very different from those recorded by a positive electrode on the right arm (or right leg, left leg, etc. ). It’s easy to see why. A wave of depolarization moving toward a positive electrode causes a positive deflection on the EKG. A wave of depolarization moving away from a positive electrode causes a negative deflection. Look at the figure below. The wave of depolarization is moving left to right, toward the electrode. The EKG records a positive deflection.

Positive electrode

EKG

Depolarization

A wave of depolarization moving toward a positive electrode records a positive deflection on the EKG.

Now look at the following figure. The wave of depolarization is moving right to left, away from the electrode. The EKG therefore records a negative deflection.