An ECG can tell if the heart is beating normally, or it can detect heart disease or problems with the heart’s electrical conduction system. It records the rate and regularity of heartbeats, and can tell the size and position of the chambers of the heart. An ECG recording can show signs of damage to the heart and the effects of drugs or devices such as pacemakers and ICDs.

How The Test Is Performed

An ECG is a safe, commonly performed heart test that rarely causes discomfort. The patient lies down and "electrodes" at the end of wires (or leads) are attached to each arm, leg and the chest. Electrodes are sticky patches that attach to the skin or suction cups applied with conductive paste that are easily peeled off once the procedure is completed. The places where the electrodes are attached are cleaned, and in some cases, it may be necessary to shave or clip the hair.There are no needles used and the test is painless. The ECG takes about ten minutes from start to finish, but the actual recording of the heart's electrical activity usually is done in a matter of seconds. Patients are required to remain still, and are sometimes asked to hold their breath for short periods of time.

How To Prepare For The Test

There is little preparation necessary for an ECG, and you may eat or drink fluids before and after the test. You may be asked to wear a hospital gown for the test, and all jewelry should be removed. Also, be sure to tell your doctor or the person who performs the ECG if you are taking any medications. Some medications can affect the electrical activity of the heart, and this information is important in order for the doctor to interpret the exam correctly.

An ECG May Be Performed to Identify:

• The cause of abnormal heart rhythms (arrhythmias) which may be caused by electrical signals that are too slow, too fast, or do not follow the normal path of conduction through the heart.
• Heart muscle damage.
• A decrease in oxygen supply to parts of the heart.
• Signs of a recent or prior heart attack, or myocardial infarction (MI). Sometimes an ECG warns of an evolving MI.
• Whether a pacemaker or ICD is functioning appropriately.
• The effects of medications, specifically antiarrythmic drugs.

The 12-Lead ECG

The most common type of ECG is called a 12-lead ECG. In this test, 12 electrodes are attached to the skin of the arms, legs and chest to give 12 different views of the heart as electrical impulses travel through the heart muscle. Each of 12 views created by the ECG is shown in a short segment on the printed ECG report generated by the ECG machine. Often, a longer reading of one of the 12 views is printed out on a "rhythm strip."

A Rhythm ECG

A bedside monitor that performs electrocardiography is called a rhythm ECG, which usually has from one to three electrodes. This is used when patients are hospitalized and require monitoring of the heart for an extended period of time.

ECG Recording

The electrical activity of the heart forms a series of waves and complexes that have been labeled (in alphabetical order) the P wave, the QRS complex, the T wave and the U wave. The waves are separated by regular intervals in patients with a normal heartbeat. When the intervals are not regular, it may be a sign of heart disease or other problems.