Electrocardiogram

An EGC can detect insufficient blood flow to the heart and whether you may have had previous or new heart attacks, even if you are not aware of them. It can also pinpoint the areas of your heart damaged by previous attacks.

It can indicate whether there is thickening, or hypertrophy, in the wall of the left ventricle, the heart’s most important pumping chamber, and aid with the diagnosis of valve disorders and various diseases of the heart muscle.

It also detects and monitors abnormalities in the heart’s rhythm, known as arrhythmias, which are caused by problems with the heart’s electrical impulses.

Types of ECG

There are a number of different types of ECG and your doctor or cardiologist may want you to have more than one.

Standard or resting ECG. This is conducted while you lie still on a bed or examination table while your heart is monitored. This test is usually available at your doctor’s surgery as well as at more specialised centres.

Exercise or exercise stress ECG. This type of test may be recommended for people with suspected angina because it can help to identify a more serious artery blockage, which in turn would require further testing such as a coronary angiogram(catheter X-ray of the heart arteries). It can also help determine how severely you are affected and can give a baseline for future follow-up. In a stress test you exercise with various degrees of intensity, usually on a treadmill or exercise bike, in a closely monitored environment, usually a cardiologist’s clinic or hospital.

This test is paced carefully to increase your activity until you reach your maximum heart rate. During this test, your heart rate and blood pressure are measured every few minutes, and your ECG readings are monitored continuously.

In the case of angina, an exercise stress test is useful because it can show what your heart is doing when it needs more blood and oxygen and how well your coronary arteries (the arteries that supply blood to your heart muscle) are able to supply it.

Official guidelines suggest that exercise ECGs should generally not be done if a person has problems including unstable angina, a recent heart attack, heart muscle failure, heart muscle infection (myocarditis) or potentially serious heart rhythm abnormalities. Care should also be applied to anyone with problems such as very high blood pressure, heart valve disease and cardiomyopathy (heart muscle abnormalities). In someone with chest pain but a negative ECG and blood tests, a stress ECG can uncover what might really be going on.

Pharmacological stress test ECG. This test will be used if you’re too unwell or there is another reason you can’t physically exercise. It involves being given a medication that simulates the effects of exercise on your heart. This enables doctors to assess your heart’s performance under stress without you having to exercise physically.

Nuclear Stress test, also known as a myocardial perfusion test. This involves the injection of a short lived radioactive substance which is picked up by heart muscle under stress and identifies areas of the heart suffering a shortage of blood. It is sometimes used in the preparation for heart surgery as well as monitoring the benefits of other treatments.

A 24-hour ECG, also known as a Holter monitor or ambulatory ECG. An ambulatory electrocardiograph is taken wearing a portable ECG machine on a belt around your waist for 24 hours to provide a picture of your heart’s electrical activity – its electrical rhythm – over a longer period. Electrodes are placed on your chest and attached to the device.

An ambulatory ECG is generally useful in arrhythmia diagnosis – detecting extra beats or abnormal rhythms – and potentially revealing what your heart is doing when you experience symptoms, although you don’t need to have symptoms in order for the Holter monitor to detect a problem.

Portable cardiac event recorder. This device is an even longer term ECG in which a portable device is used to track your heart’s activity, usually only when you have symptoms. This may also involve the insertion of a small device called an implantable loop recorder (ILR) under the skin of your chest. It can then monitor, record and replay important information about your heart’s activity.

Other tests. There are also small ECG devices which you can carry around with you and press to your chest when you’re experiencing symptoms to measure what might be going on.

The type of ECG you have will depend on the condition for which you’re being assessed, as ECG is used to diagnose a number of different kinds of heart disease.

ECG: what to expect and how to prepare

Having an ECG is painless and non-invasive. The electrodes are stuck to your body with a simple adhesive. In some cases, body hair can impair their sticking ability, so very small patches will be shaved so they can be attached to the smooth skin beneath. It’s a good idea to wear loose comfortable clothing that will make attaching and wearing the electrodes easy, especially if you’re having an exercise stress test where you will be asked to walk or run on a treadmill. Similarly, if you’re having an exercise stress test, avoid having a large meal before it.

Because certain medication can affect the results of the ECG, you might be asked to stop taking it beforehand.

Generally, a standard or exercise ECG takes up to 15 minutes.

If your doctor wants to monitor your heart’s activity over a longer period, you’ll be given a portable ECG – known as a Holter monitor – to take home for 24 hours. You’ll be given full instructions on how to use it.

If you need a cardiac event recorder to monitor your heart’s activity for longer, you will also be given detailed instructions on how to use it.

ECG results: what they can show

During an ECG your heart’s rhythm and electrical activity is recorded in the form of a graph, which needs to be read by a trained clinician.

While an ECG generally provides an accurate picture of your heart’s activity, it is not infallible and its accuracy will depend on both the skill of the person reading it and on what your heart was doing at the time it was taken. It’s quite possible to have a ‘normal’ ECG reading and have coronary artery disease, or be disease free and have an ‘abnormal’ reading. That’s why an ECG is normally used in conjunction with other tests that can help give as complete a picture as possible.

In the case of coronary artery disease, for example, the read-out can show how hard or efficiently your heart was working during exercise and how quickly – or slowly – it recovered once the exercise stopped. This can help reveal whether or not there is a problem with blood supply when your heart is under pressure.

It can also show how your heart may have worked harder and then recovered if you were experiencing symptoms such as angina. If you’ve already had a heart attack, lack of electrical activity in certain areas of the heart can show that there is damage, and in some cases, where it is.

If you're experiencing an irregular heart beat, or arrhythmia, having an ECG can help to pinpoint the kind of arrhythmia it is, under what circumstances it occurs and provide some insight into the source of the problem, which will in turn help with deciding the best treatment strategy.

If there is a problem with the heart’s pumping ability or valves, the ECG will also show this, so further investigation and treatment can be considered.

The results of your ECG will be used to help establish the type and extent of your heart disease and, with further investigations, your treatment options.

Risks of an ECG

An ECG is a very low risk test. The way the ECG machine is structured means there is no risk of electrocution; and where there is no incision there is no risk of infection.

The most significant risk of complication – which is still low – is experiencing discomfort or in rare instances a heart attack during an ECG exercise stress test. However, the stress test is closely controlled and your heart monitored to avoid this. The test should always take place in a specially prepared environment with expert help at hand.

Next: Cardiac CT scanning

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