Electrocardiograph (ECG)

Also called electrocardiogram

An electrocardiograph (ECG) is a test that is used to measure the electrical activity of the heart. Read about when it is done and related tests such as an exercise ECG stress test or event monitoring.

Key points

  1. An ECG is the most common test for assessing heart conditions.
  2. It is a painless test that measures the electrical activity of the heart and only takes a few minutes to do (about 5 to 10 minutes).
  3. GPs are often able to do the ECG in their surgery but sometimes you will need to be referred to a hospital.
  4. By looking at the pattern of spikes and dips on your ECG, your doctor will be able to gauge how your heart is working. 

What is an electrocardiograph (ECG)

An electrocardiograph (ECG) is a test that is used to measure the electrical activity of the heart.

  • This electrical activity causes contractions of the heart muscle, which results in the heart's pumping action.
  • The ECG is recorded on paper, as spikes and dips called waves. By assessing the pattern of these waves, your doctor can gauge the rhythm and the rate of your heart beat.

When is an ECG done?

An ECG  may be done as part of a routine checkup, for example, before surgery, to check how well your heart is working. An ECG may also be done:

  • To check the health of the heart when other diseases are present such as diabetes, high blood pressure, high cholesterol, cigarette smoking and a family history of early heart disease.
  • To find the cause of symptoms that may indicate a problem with your heart such as rapid and irregular heartbeats (palpitations), and chest pain. 
  • To find out if the walls of the heart chambers are too thick.
  • To monitor how well medicines are working and to see if they are causing side effects that affect the heart.  
  • To assess how well mechanical devices that are implanted in the heart are working such as pacemakers, which help to control the heartbeat . 

How to prepare for an ECG

For the most part, no special preparations are necessary. However:

  • Avoid exercising immediately before an electrocardiograph. Physical activity, such as climbing stairs, or exercise may increase your heart rate and affect the results. 
  • Tell your doctor or nurse if you are taking medication for your heart. You will be advised about whether you need to stop taking these medications before having a heart test, and how soon you should start taking it again after the test.

How is an ECG done

  • An ECG can often be done at the doctors surgery by the doctor, a trained nurse or a technician. In some situations, you may need to be referred to a hospital.
  • During the ECG test, small sticky patches, which are metal electrodes, will be attached to your arms, legs and chest. Wires connect these electrodes to the ECG machine, which detects the electrical impulses that occur at each heartbeat and records them on to paper or computer. 
  • During the test, you lie quietly on a table or bed while the machine records your heart’s electrical activity. You will need to lie as still as possible, without talking, and breathe normally. This is called a resting ECG as it records the heart's activity while you are at rest, and not exerting yourself.
  • After the procedure, the electrodes will be removed.

Results

  • You will usually be told the results of your ECG straight away unless it needs to be sent away for reporting by a specialist. 
  • Your doctor will look at the pattern of spikes and dips on your ECG to check the electrical activity in different parts of your heart, and show how your heart is working. Your doctor will look for a consistent, even heart rhythm and a heart rate between 50 and 100 beats a minute. Having a faster, slower or irregular heartbeat provides clues about your heart health. It is important to note that a normal ECG does not exclude heart disease, and further testing may be necessary.

Specialised ECG tests

Sometimes the ECG recording at rest (while your are lying down or resting) does not provide enough information and your doctor may request a more specialised ECG test such as:

Exercise ECG or exercise tolerance test (ETT)

  • This records your ECG while you are exercising. It is sometimes called a "stress test" or a "treadmill test." During an exercise ECG, you may either walk on a motor-driven treadmill or pedal a stationary bicycle. 
  • A resting ECG is always done before an exercise ECG test, and results of the resting ECG are compared to the results of the exercise ECG. Some heart problems only appear when your heart needs to work harder. This test helps to show how your heart copes under stress.

Cardiac holter monitoring test

  • This type of ECG records the electrical activity of your heart while you do your usual activities. Many heart problems are noticeable only during certain activities. These include exercise, eating, sex, stress, bowel movements, and even sleeping.
  • A constant 24-hour recording is more likely to find abnormal heartbeats that occur during these activities. For this test you wear a small, portable ECG machine for 24 or 48 hours and during this time your heart rate and rhythm are recorded.

Event monitoring

  • This is used to record your heartbeat when you experience symptoms such as dizziness, black outs, chest pain or palpitations. When you experience symptoms, you will need to press a button to start the recording

Learn more

The following links provide further information on electrocardiograms. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Heart tests  Heart Foundation New Zealand
Electrocardiograph Heart Foundation New Zealand
Exercise tolerance test Heart Foundation New Zealand
24 or 48 hour cardiac holter monitoring Heart Foundation New Zealand
Event monitoring Heart Foundation New Zealand
Electrocardiogram (ECG) Patient Info, UK

Credits: Sandra Ponen. Reviewed By: Dr J Bycroft