Diagnostic Procedures: Electrocardiograms

While you are at Cedars-Sinai Medical Center, you may have frequent electrocardiograms (ECGs) done. This painless test gives an electrical picture of how your heart is working. The test requires only that you lie still while the technician puts electrodes (which can record the electrical activity of your heart and are attached by sponge pads) on your arms, legs and chest. In some cases, shaving chest hair may be needed so there is better contact between the electrodes and the skin. The electrodes are connected by wires to an ECG monitor, which looks like a television. The test takes about five minutes.

  The electrodes pick up and measure the electrical activity of your heart. The scale on the left measures how intense the electrical current is (the voltage). The scale across the bottom of the electrocardiograph shows the elapsed time for each segment of the electrical current.

An electrocardiogram shows a pattern of upward waves and downward waves as the electrical current grows stronger as your heart's muscle contracts and begins to fade as the muscle relaxes between beats. Doctors have labeled key points in the pattern of waves. For example, in the illustration at left, P , where the wave begins rising is due to the contraction of the atrium (upper chamber of the heart). This is sometimes called the atrial complex. The other points - Q, R, S and T - are part of the action of the ventricles (lower chambers of the heart). They are sometimes called the ventricular complexes.

Some of the things an electrocardiogram can tell your cardiologist are your heart rate, how regularly your heart is beating as well as the size and position of your heart's chambers, any damage to your heart and the effects of any drugs or devices used to regulate your heart. An electrocardiogram can also show whether a coronary artery is blocked and where the block is located. Other types of conditions including high blood pressure, thyroid disease and some types of malnutrition may appear on an electrocardiogram.

Doctors sometimes talk about a particular portion of the activity shown on an electrocardiogram by referring to the starting point and the ending point. For example, a QT interval is that part of an electrocardiogram that shows the time it takes for the electrical system to fire an impulse through the ventricles and then recharge. In other words, this describes the time it takes for the heart muscle to contract and then recover.

Room Monitors

While you are in the Intensive Care Unit (ICU), an ECG machine will continuously monitor you. The electrodes will be placed on your chest. The electrical activity of your heart is continuously recorded to help plan your therapy.

ECG electrodes are quite sensitive. Don't be frightened if your movement causes the monitor's alarm to go off. This is a safety feature to alert nurses and doctors of any significant changes in the rate or rhythm of your heartbeat. 

Holter Monitors

Sometimes it is important to have a record of your heart's activity during the course of a day's normal activities. If so, your doctor may order a Holter monitor. This monitor is about the size of a personal mp3 player, and is connected by leads to electrodes on your chest. You wear the monitor as you move about. It keeps a constant record of your heart rhythm on a tape recorder for 24, 48 or 72 hours.