Electrocardiogram (ECG)

What is an electrocardiogram (ECG)?

An electrocardiogram (also known as an ECG or EKG) is a simple, non-invasive test that records the electrical activity of the heart.

What is the purpose of an ECG?

The purpose of an ECG is to check for any abnormalities of the heart that include its rhythm or heart rate. An ECG can also assess other aspects of heart function, such as the thickness of the heart muscle (hypertrophy).

Heart conditions that may be detected during an ECG include:

• arrhythmias (abnormal heart rhythms)
• coronary artery disease (narrowed or blocked arteries in the heart)
• heart attack
• cardiomyopathy (thickening or enlargement of the hearts walls)
• other conditions that may disrupt the heart’s electrical system

When do I need an ECG?

Your doctor will perform an ECG if you have symptoms that may indicate an issue with the heart. These symptoms may include:

• chest pain
• palpitations
• dizziness
• shortness of breath
• fatigue
• fainting

An ECG may be performed alongside other tests to ensure an accurate diagnosis. These tests may include:

• an echocardiogram (heart ultrasound)
• a chest x-ray
• an MRI or CT scan
• a coronary angiogram (which checks for narrowing in the arteries)

As an ECG only captures the heart’s electrical signal over a short period of time, your doctor may choose to follow up your standard ECG with longer ECGs if your symptoms tend to come and go.

These ECGs may include:

• a Holter monitor, which records the heart’s electrical activity over a 24- or 48-hour period
• an event monitor, which is worn for around 30 days and records irregular heart rhythms when they occur

How is an ECG performed?

Typically, ten small, sticky sensors (electrodes) are put on the skin on the chest, arms, and legs. These sensors are connected by leads to the ECG machine.

The ECG machine records the electrical activity of the heart each time it beats. This activity is displayed as a trace on the screen and as a paper print out.

The doctor will review the trace to check whether there are any features that may indicate an issue with the heart.

How do I prepare for an ECG?

No specific preparation is required for an ECG. You can eat and drink as normal before the test, unless advised otherwise by your doctor.

Your doctor will need to know what medications and/or supplements you are on as these may affect the results.

You will need to remove your upper clothing during the test, so it is best to wear a top and pants or a skirt to make this process easier.

Hair on the chest may need to be shaved to allow the electrodes to stick to the skin. Bras with underwire will need to be removed as the underwire can interfere with the test.

The test can be performed in your doctor’s office, in a clinic, or in a hospital room, and it generally takes less than 15 minutes, with the placement of the electrodes and leads making up the bulk of the time.

Are ECGs safe and do they have any side effects?

An ECG is a quick, safe, and painless test. There is no risk of electrical shock as the electrodes do not produce electricity, they only record the electrical activity of the heart.

The sticky sensors may cause minor irritation when removed from the skin – similar to the irritation that occurs when removing a Band-Aid. If you have an allergy to adhesives, it is best to advise your doctor before the test.

How does an ECG differ to a stress test or exercise ECG?

A stress test, which is also called an exercise ECG or stress ECG, is an ECG performed during physical activity. As opposed to a standard ECG, which records the heart’s electrical activity at rest, a stress test records the heart’s electrical activity when the heart is under exertion. A stress test is usually performed on a treadmill but may be performed using medication for those who cannot exercise or walk on the treadmill.

Your doctor will choose which ECG to perform based on whether they want to assess your heart rhythm during rest, or when the heart is working hard. In some cases, both a standard ECG and a stress test may be required to make a diagnosis.