Electrocardiogram (ECG)

Published by Bupa's Health Information Team, April 2010.

This factsheet is for people who are having an electrocardiogram (ECG), or who would like information about it.

An ECG records the rhythm and the electrical activity of the heart. An ECG is a test used to find out if the heart is healthy.

You will meet the doctor, nurse or technician carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.

How the heart works

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About ECG

An ECG is a simple test to record information about your heart beat. An ECG measures the electrical signals that cause your heat to beat. Wires are connected to your arms, legs and chest to pick up the electrical signals. These signals can be seen on a screen or are traced out on a piece of paper.

There are a number of reasons why you may need to have an ECG. You may have one:

• to check for problems with your heart if you're having symptoms such as dizziness, chest pain or an abnormal heart rate
  
• to check how well your heart is working before an operation
  
• as part of a routine health check-up

An ECG can identify problems with your heart including:

• a heart attack
  
• an enlarged heart that is working under strain
  
• fast, slow or irregular heartbeats called arrhythmias

There are a number of different types of ECG. These are listed below.

• The standard ECG which is sometimes called a resting ECG. This is taken while you're resting.
  
• An exercise ECG (also known as a stress test or treadmill test) is taken while you're exercising. This shows how your heart copes under stress. The test can help to diagnose coronary heart disease (when the arteries to your heart become narrowed) and assess how severe it is.
  
• A 24-hour ECG, sometimes called a Holter monitor or ambulatory ECG, is a test where you wear an electronic recorder for 24 hours. This shows the activity of your heart over a day and night. It's useful for showing any irregular heartbeats (arrhythmia).
  
• Cardiac event recorders can record your heartbeat over a longer period of time. They include portable event recorders, which you use to record your heart beat when you get symptoms, and implantable loop recorders (ILR), which are put in under the skin in your chest to continuously monitor your heartbeat. An ILR is useful for recording your heart beat if you have dizzy spells or if you faint. They can stay in place for up to a year or longer.

Preparing for an ECG

A standard ECG can often be done at your GP practice. No preparation is normally needed for this.

If you're having an exercise ECG, 24-hour ECG or cardiac event monitoring you will need to go to hospital to have the test or have the equipment fitted. You will have your ECG as an out-patient and should follow any instructions given to you in your appointment letter.

You should wear comfortable clothes for an exercise ECG and don't have a heavy meal before the test. If you're taking certain medicines, for example beta blockers, you may be asked not to take them before an exercise ECG.

Your doctor, nurse or technician will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to understand what will happen, and you can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead, which you may be asked to do by signing a consent form.

What happens during an ECG

Resting ECG

The standard, resting ECG takes a few minutes. You will be asked to undress to the waist and lie down on a bed or couch. A number of sticky patches called electrodes will be stuck onto your arms, legs and chest. If you have a lot of hair on your chest, some small patches may need to be shaved to allow the electrodes to make contact with your skin.

The electrodes are attached to a recording machine by wires. When your heart beats, it produces electrical signals which are picked up by the electrodes and transmitted to the recording machine. The machine then prints a record of your heartbeat onto a paper strip. You should lie still when the recording is being taken as moving can affect the reading.

                            Resting ECG

Exercise ECG

For an exercise ECG, electrodes from the recording machine are connected to you with wires in the same way as a standard ECG. Your heart rate and blood pressure will also be recorded. You will then be asked to exercise, either by walking on a treadmill or cycling on a stationary exercise bike. If you aren't able to exercise, sometimes a drug called adenosine can be used to stimulate the effect of exercise.

The exercise will be gentle to start with and gradually becomes more strenuous, for example, by increasing the speed or the slope of the treadmill. The doctor or technician will monitor your ECG along with your blood pressure and heart rate, every few minutes while you're exercising.

The test will last between a few minutes and 15 minutes. It will be stopped when the doctor or technician has the readings he or she needs. The test may also be stopped if your blood pressure becomes too high, if you have chest pains or if you become short of breath. You can ask for the test to be stopped if you feel unwell.

Once your ECG and blood pressure have returned to normal, you will be able to go home.

                                                           Exercise ECG

24-hour ECG

For this test, you will be asked to wear a small portable recorder, attached to a belt around your waist. Wires from the recorder are connected to three or four small sticky patches (electrodes) on your chest.

You will usually have the recorder fitted at a hospital. You can go about your normal activities for the day, while keeping a diary of everything that you do and noting when you feel symptoms. You shouldn't have a bath or shower with the recorder on. At the end of the 24 hours, you can remove the electrodes and recorder and return it to the hospital.

                                                               24-hour ECG

Cardiac event recorders

A portable event recorder is a small electrical device that you use when you have symptoms. When you have symptoms, such as palpitations, you place the device on your chest and switch it on to record your ECG. With most portable event recorders, you will be able to send the results of the recording to the hospital by holding the device to a phone. The doctor or technicians at the hospital can then analyse your results and tell what to do next.

An implantable loop recorder (ILR) is a small, slim device that is inserted just under the skin on the front of your chest. This is done using a local anaesthetic. It continuously monitors your heartbeat and records any unusual heartbeats. You can also start a recording if you notice any symptoms.

What to expect afterwards

If your GP carries out your ECG, he or she may discuss the results with you immediately after the test. If you have the test in hospital, your results will be sent to the doctor who requested your test, and he or she will discuss them with you at your next appointment.

If your doctor thinks there is a problem, you may need to have further heart tests.

If your ECG is normal, your doctor may suggest other tests to explain what is causing your symptoms.

What are the risks?

A standard ECG is a very simple procedure and is completely painless. The recording machine can't give you an electric shock or affect your heart in any way. There is a very small risk of complications with the exercise ECG. The extra demand on your heart from exercising may cause:

• chest pain (angina) or a heart attack
  
• shortness of breath
  
• abnormal heartbeats (an arrhythmia)

You will be monitored at all times during the test and told to stop if the technician or doctor thinks there is a risk of you becoming unwell. A medical team will always be on hand in case of emergency.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.