Electrocardiogram (ECG or EKG)

An electrocardiogram (ECG or EKG), an electrical recording of the activity of the heart, is routinely performed to evaluate congenital heart defects. The ECG records the timing and duration of each electrical phase of the heartbeat. The ECG can provide clues about thickening of the heart muscle, structural abnormalities, heart rhythm abnormalities, inadequate blood and oxygen supply to the heart muscle, or enlargement of the heart's chambers--quickly, inexpensively, and with no risk to the patient. If the ECG indicates an abnormality, additional testing is usually needed to confirm a diagnosis.

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In an ECG, the electrical activity of the heart is recorded by electrodes that are temporarily attached to the skin with sticky pads. The electrodes transmit the heart's electrical impulses to a device that records these impulses as wave-shaped lines on a scrolling paper or on a monitor. This output is called a tracing. Different waves represent different areas of the heart. The main components of the ECG tracing are:

• the P wave, representing electrical currents in the atria,
• the QRS complex, representing electrical currents in the ventricles
• the T wave, representing the electrical recovery period of the ventricles

An ECG can reveal the strength and duration of the electrical impulses in the heart. It also can show a deviation in the electrical firing sequence of the heart, which normally starts in the atria and proceeds to the ventricles.

The actual ECG reading takes only 30 to 60 seconds. The test requires no preparation on the part of the patient. Usually, 12 to 15 electrodes are attached to various parts of the body, including one on each arm and each leg and six across the chest. The remaining electrodes are attached at other sites in the chest, neck, and back. After the leads are attached, the readings are recorded. There is no discomfort associated with this test. This section includes information on other types of ECG used in the evaluation of congenital heart defects.