A quick, painless recording of the heart's electrical activity, used to assess heart rate, rhythm and conduction.
Cardiac investigation
Electrocardiogram (ECG)
What this test is and when it helps
An electrocardiogram, or ECG, records the electrical signals that make the heart beat. Sticky patches called electrodes are placed on the chest, arms and legs and connected to a recording machine. The machine only picks up signals. It does not send any electricity into the body, so there is no shock.
A resting ECG may be recommended for palpitations, dizziness or blackouts, chest pain, breathlessness, a heart murmur, high blood pressure, a family history of heart disease or before some medicines. It is also used to follow an established heart condition.
Dr Mark Cassar personally interprets the tracing, allowing it to be considered alongside your symptoms, examination findings and any previous results.
A resting ECG differs from Holter and ECG monitoring, which records the rhythm for a day or longer, and from an echocardiogram, which uses ultrasound to show the structure of the heart.
What an ECG can assess
Heart rate and rhythm
The tracing shows whether the heartbeat is regular, unusually fast or slow, or irregular, as in atrial fibrillation.
Electrical conduction
It shows how the signal travels through the heart, including any delay or block along the way.
Strain or previous damage
Some patterns suggest strain on the heart muscle or damage from an earlier heart attack. The electrical effects of certain medicines can also be seen.
An unusual tracing does not always mean heart disease, because some changes are normal variations. Findings are interpreted in context rather than in isolation.
What happens during the test and how results are interpreted
You usually take off your top and lie back behind a screen, and you can ask for a chaperone. A standard 12-lead ECG uses ten patches, which together give twelve views of the heart's electrical activity, called leads. Some chest hair may be trimmed so the patches stick well.
The recording takes a few minutes. You lie still and breathe normally, because moving and talking blur the trace. Removing the patches feels like peeling off a plaster, and a mild rash is occasional.
Many machines print an automated interpretation. This is a prompt rather than a diagnosis, and the tracing needs to be reviewed by a clinician.
A resting ECG records only a short period. A normal tracing is reassuring, but it does not exclude a rhythm problem that comes and goes, and it does not measure how strongly the heart pumps. It cannot exclude coronary artery disease either, because narrowed arteries can leave a resting tracing normal.
When another test may be needed
Holter and ECG monitoring
Records the rhythm over a day or longer when symptoms come and go.
Echocardiogram
Uses ultrasound to assess chamber size, valves and pumping function.
Stress imaging
Assesses the heart under controlled stress when symptoms suggest reduced blood flow.
Frequently asked questions
Is an ECG painful?
No. The recording itself is painless. The only discomfort is usually from taking the patches off.
Will I have to undress?
You normally take off your top and lie behind a screen. Say if you would like a chaperone, or if anything about privacy concerns you.
Is an ECG the same as an echocardiogram?
No. An ECG records electrical activity. An echocardiogram uses ultrasound to show the heart's structure and movement.
Does a normal ECG mean my heart is healthy?
Not necessarily. It is reassuring for the moment it was recorded, but symptoms that come and go, or that happen on exertion, may need further tests.
Do I need to prepare?
Wear a top that is easy to take off and avoid body lotions or oils on the chest. Take your usual medicines unless you are told otherwise.
Discussing whether an ECG is appropriate
Dr Mark Cassar can review your symptoms, examination findings and previous results, and arrange or perform an ECG where clinically appropriate.
Or call 020 3198 9826 or email medicalsecretary@drcassar.co.uk
Not an emergency service. Call 999 for a medical emergency. Do not wait for a private appointment. Medical information disclaimer.