Electrocardiogram: Tracing the electrical path through the heart

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Electrocardiogram: Tracing the electrical path through the heart

An electrocardiogram is a simple test that provides valuable clues about your heart health.

Each beat of your heart is triggered by an electrical impulse generated from special cells in the right upper chamber of your heart. An electrocardiogram — also called an ECG or EKG — records these electrical signals as they travel through your heart. Your doctor can look for patterns among these heartbeats and rhythms to diagnose various heart conditions.

Who needs an ECG?

An electrocardiogram is a painless, noninvasive way to diagnose many common types of heart disease. Your doctor may use an ECG to detect irregularities in your heart rhythm, structural abnormalities in your heart, or problems with the supply of blood and oxygen to your heart. An ECG can also confirm if you're having a heart attack or if you've had a heart attack in the past.

How do you prepare for an ECG?

No special preparations are necessary. However, avoid drinking cold water or exercising immediately before an electrocardiogram. Cold water can produce potentially misleading changes in one of the electrical patterns recorded during the test. Physical activity, such as climbing stairs, may increase your heart rate.

What happens during an ECG?

An electrocardiogram can be done in the doctor's office or hospital. After changing into a hospital gown, you'll lie on an examining table or bed. Various electrodes — often 12 to 15 — will be attached to your arms, legs and chest. The electrodes are sticky patches applied with a gel to help detect and conduct the electrical currents of your heart.

You can breathe normally during the electrocardiogram. Make sure you're warm and ready to lie still, however. Moving, talking or shivering may distort the test results.

A standard ECG takes just a few minutes. If you have a heartbeat irregularity that tends to come and go, however, it may not be captured during the few minutes a standard ECG is recording. To work around this problem, your doctor may recommend another type of ECG:

  • Holter monitoring. Also known as an ambulatory ECG monitor, a Holter monitor records your heart rhythms for an entire 24-hour period. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap. While you're wearing the monitor, you'll keep a diary of your activities and symptoms. Your doctor will compare the diary with the electrical recordings to help determine what triggers your symptoms.
  • Event recording. If your symptoms are infrequent, your doctor may suggest wearing an event recorder. This device is similar to a Holter monitor, but it allows you to record an ECG just when the symptoms are happening. You can send the ECG readings to your doctor through the phone line.

What's the difference between an ECG and a stress test?

If your heart problems occur most often during exercise, your doctor may ask you to walk on a treadmill or ride a stationary bike during an ECG. This is called a stress test. If you have a medical condition that makes it difficult for you to walk, medication may be injected to stimulate your heart.

What do the results mean?

Your doctor will look for a consistent, even heart rhythm and a heart rate between 60 and 100 beats a minute. Variations provide a wealth of clues about your heart health, including:

  • Heart rate. Normally, heart rate can be measured by simply checking your pulse. But an ECG may be helpful if your pulse is difficult to feel or too fast or too irregular to count accurately.
  • Heart rhythm. An ECG can help your doctor identify an unusually fast heartbeat (tachycardia), unusually slow heartbeat (bradycardia) or other heart rhythm irregularities (arrhythmias). These conditions may occur when any part of the heart's electrical system malfunctions. In other cases, medication can trigger arrhythmias.
  • Heart attack. An ECG can often show evidence of a previous heart attack or one that's in progress. The patterns on the ECG may indicate which part of your heart has been damaged, as well as the general extent of the damage.
  • Inadequate blood and oxygen supply to the heart. An ECG can often help your doctor determine whether chest pain is caused by reduced blood flow to the heart muscle, a prime characteristic of coronary artery disease.
  • Structural abnormalities. An ECG can provide clues about enlargement or inflammation of the heart, congenital abnormalities and various other heart problems.

What are the risks of an ECG?

An electrocardiogram is a safe procedure. There may be minor discomfort when the electrodes are removed. Rarely, a reaction to the electrodes may cause redness or swelling of the skin. During a stress test, exercise or medication — not the ECG — may trigger heart distress.

What happens after the test?

If your electrocardiogram is normal, no further testing may be needed. If the results are concerning, you've had a heart attack or your doctor suspects heart disease, you may need a repeat ECG or other diagnostic tests. Treatment depends on what's causing your signs and symptoms.

    Last Updated: 06/30/2006
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