Electrocardiogram

What is it?

According to the NHLBI: an electrocardiogram (ECG or EKG) is a simple, painless test that detects and records the heart's electrical activity. It shows the speed of the heartbeat, whether the rhythm is regular or not, and the strength and timing of electrical signals in parts of the heart.

According to MedlinePlus the recording consists of the P wave (activity of the upper chambers), the QRS complex (the lower chambers), and the T wave (recovery of the heart).

Its types according to the NHS: a resting ECG where you stay still during the recording; a portable ECG usually worn for 24 to 48 hours and possibly up to 7 days with a device carried on a belt; and an exercise ECG in hospital while walking on a treadmill or riding a bicycle, usually taking between 40 and 60 minutes.

Why is it done?

According to MedlinePlus it is used to detect abnormal heart activity that may indicate disease or damage, and to help diagnose and monitor arrhythmia, cardiomyopathy, coronary artery disease, heart attack and heart failure. It is also used to assess readiness for surgery and the effect of medicines, to monitor pacemakers, and to detect previous undiagnosed heart attacks.

The NHS states that it is done when a heart attack, coronary artery disease or an irregular heartbeat is suspected, and also for people with a diagnosed heart condition or before or during certain medicines.

Preparation

According to MedlinePlus: no special preparation is needed, but some medicines may affect the accuracy of the result, so tell your care provider about all your medicines and supplements and do not stop any medicine except on their instructions.

According to the NHS: wear clothes that are easy to remove, avoid moisturisers, oils and powder on the skin, and chest hair may need shaving. Before an exercise ECG avoid heavy meals and caffeine.

How is it done?

According to the NHLBI: you lie still on a table, and a nurse or technician attaches several electrodes to the skin of the chest, arms and legs, and the skin may be shaved to attach them. The electrodes are connected by wires to a machine that records the electrical activity on graph paper or a computer, and are then removed after the test. The test takes minutes according to MedlinePlus.

In an exercise ECG, according to the NHS, the intensity of walking or cycling is gradually increased during the recording.

Understanding the result

According to MedlinePlus the care provider checks the regularity and rhythm of the heartbeat, and an abnormal result may indicate a heart condition but the diagnosis may need other heart tests. According to the NHS the result may arrive on the same day or after weeks depending on the type of ECG, and follow-up appointments may be needed.

Risks and side effects

According to the NHLBI: there are no serious risks; the ECG does not give electric shocks, and a mild rash may appear where the electrodes were, which usually goes away without treatment. The NHS mentions possible mild skin irritation and slight discomfort when the stickers are removed.

Limits of the test

According to MedlinePlus the result alone may not be enough for a diagnosis and other heart tests are requested; and for intermittent symptoms longer monitoring may be recommended with a Holter monitor (up to two days) or an event monitor (weeks to years).

After the test

Follow-up differs according to the result and condition, and is decided by the doctor; the NHS states that some conditions need a follow-up appointment. This page does not cover other details.

Common questions