An electrocardiogram (ECG) measures the heart's electrical activity to help evaluate its function and identify any problems that might exist. The ECG can help determine the rate and regularity of heartbeats, the size and position of the heart's chambers, and whether there is any damage present.
There is nothing painful about getting an ECG. The patient is asked to lie down, and a series of small metal tabs (called electrodes) are fixed to the skin with sticky papers. These electrodes are placed in a standard pattern on the shoulders, the chest, the wrists, and the ankles. After the electrodes are in place, the person is asked to hold still and, perhaps, to hold his or her breath briefly while the heartbeats are recorded for a short period. The patient also might be asked to get up and exercise for a while.
The information is interpreted by a machine and drawn as a graph. The graph consists of multiple waves, which reflect the activity of the heart. The height, length, and frequency of the waves are read in the following way:
A person's heartbeat should be consistent and even. ECGs look for abnormally slow and fast heart rates, abnormal rhythm patterns, conduction blocks (short-circuits of the heart's electrical impulses that cause rhythm inconsistencies between the upper and lower chambers) — and four types of heart damage:
Computerized ECGs can be combined with other tests to provide a multimedia account of the heart. These additional tests include echocardiograms (which are basically "ultrasound" tests that bounce sound off the heart and use the echoes to produce an image) and thallium scans (which are kind of like X-rays and use a radioactive tracer, injected into the bloodstream, to help draw a picture of the heart).
In the past, the ECG was recorded on a machine that drew on long strips of paper, with records from each electrode presented in a standard sequence. Now the ECG tracings are stored as computer files that can be called up and printed.
Results of the ECG are available immediately. In fact, the ECG machine's computer even provides an instant interpretation of the findings as it makes the report. However, the doctor also might ask an expert, usually a cardiologist, to help analyze and interpret the ECG.
Reference ranges for heart rate and the relative lengths and sizes of the various components of the heartbeat figures vary, and diagnostic differences may be subtle, requiring an expert eye to detect them.