An electrocardiogram (ECG) is an important test in suspected heart attacks. It should be carried out within 10 minutes of being admitted to hospital.
An ECG measures the electrical activity of your heart. Every time your heart beats, it produces tiny electrical impulses. An ECG machine records these signals onto paper, allowing your doctor to see how well your heart is functioning.
An ECG is painless and takes about five minutes to perform. During the test, electrodes (flat metal discs) are attached to your arms, legs and chest. Wires from the electrodes are connected to the ECG machine, which records the electrical impulses.
An ECG is important because:
- it helps confirm the diagnosis of a heart attack
- it helps determine what type of heart attack you have had, which will help determine the most effective treatment
Types of heart attack
Heart attacks can be classified by a measurement from the ECG known as the ST segment. It corresponds to the area of damage inflicted on the heart.
Acute coronary syndrome
A heart attack is a form of acute coronary syndrome (ACS), where there is a significant blockage in the coronary arteries.
There are three main types of ACS:
- ST segment elevation myocardial infarction (STEMI)
- non-ST segment elevation myocardial infarction (NSTEMI)
- unstable angina
The three types are described in more detail below.
ST segment elevation myocardial infarction (STEMI)
A STEMI is the most serious type of heart attack, where there is a long interruption to the blood supply. This is caused by a total blockage of the coronary artery, which can cause extensive damage to a large area of the heart.
A STEMI is what most people think of when they hear the term "heart attack".
Non-ST segment elevation myocardial infarction (NSTEMI)
An NSTEMI can be less serious than a STEMI. This is because the supply of blood to the heart may be only partially, rather than completely, blocked.
As a result, a smaller section of the heart may be damaged. However, an NSTEMI is still regarded as a serious medical emergency. Without treatment, it can progress to serious heart damage or STEMI.
Unstable angina is the least serious type of ACS. However, like NSTEMI, it is still regarded as a medical emergency as it can also progress to serious heart damage or STEMI.
In unstable angina, the blood supply to the heart is still seriously restricted, but there is no permanent damage, so the heart muscle is preserved.
A number of other tests can be used to assess the state of your heart and check for related complications. However, because heart attacks are medical emergencies, some tests are usually only carried out once your initial treatment has begun and your condition has been stabilised.
Damage to your heart from a heart attack causes certain proteins to slowly leak into your blood. Enzymes are special proteins that help regulate chemical reactions that take place in your body.
If you have had a suspected heart attack, a sample of your blood will be taken so it can be tested for these heart proteins (known as cardiac markers).
The most common protein measurement is called cardiac troponin. Your troponin levels will be measured through a series of blood samples taken over the course of a few days.
This will allow damage to your heart to be assessed, and also help determine how well you are responding to treatment.
Read more information about blood tests.
A chest X-ray can be useful if diagnosis of a heart attack is uncertain and there are other possible causes of your symptoms, such as a pocket of air trapped between the layers of your lungs (pneumothorax).
A chest X-ray can also be used to check whether complications have arisen from the heart attack, such as a build-up of fluid inside your lungs (pulmonary oedema).
An echocardiogram is a type of scan that uses sound waves to build up a picture of the inside of your heart.
This can be useful to identify exactly which areas of the heart have been damaged and how this damage has affected your heart's function.
Coronary angiography can help determine whether a blockage or narrowing has occurred in the coronary arteries and, if so, to locate the exact location of the blockage or narrowing.
The test involves inserting a thin tube, known as a catheter, into one of the blood vessels in your groin or arm. The catheter is guided into your coronary arteries using X-rays.
A special fluid, known as a contrast agent, is pumped through the catheter. This fluid shows up on X-rays, and studying how it flows around and through your heart can help locate the site of any blockage or narrowing. This helps your cardiologist decide the best treatment for you.
Read our page on treating a heart attack for more information.