Whenever a muscle contracts, a chemical reaction occurs within it. In this chemical process an energy substance and oxygen are consumed, and carbon dioxide, heat, electrical currents, and other by-products are produced. The heart is an organ composed almost entirely of muscle, and the contractions of the heart with each beat are via this same chemical action as for any other muscle. The electrical impulses produced are perpetual, so in effect the body is a battery constantly giving off an electrical current. The body is a good conductor of electricity, so these impulses are relayed to the surface. Even though these electrical variations are minute, delicate electrical instruments can detect them.
The electrocardiograph is such an instrument. It picks up and records on a graph the electrical impulses from each heart beat. The extremities of the body become the poles of the “human battery” from which the recordings are taken. Others may be taken from points on the chest. The graph produced is called an electrocardiogram, or EKG, or ECG. It is a rather complex but characteristic series of oscillations recorded from each heart beat. Interpretation of the EKG is made by the cardiologist who correlates the deflections with the various mechanical events of the heart action. It is a most useful tool in the diagnosis of heart disease when correlated with the patient’s physical findings. If your doctor orders an EKG, you will either be taken to a special room or the apparatus will be brought to your bedside. While you are lying still, electrodes will be placed on both your forearms, your left leg, and perhaps your chest. A jelly substance is placed between your skin and the electrode to assure contact. Even though only one or two of these leads are used at one time, they are all placed on at the start and the changes made by switches on the machine. The standard jest when the electrodes are placed is that the patient may be “shocked” from them, but this cannot happen, for the patient is the source of the electricity and there is none being passed into the body. Rather, electricity is flowing from the body into the electrocardiograph. So never fear that any harm can come to you. The EKG recording takes but a few moments, and you will feel nothing. The only thing the patient must do is lie still. If your doctor has ordered an EKG, it will play a very important role in your diagnosis and treatment.