CT coronary angiogram

A CT coronary angiogram uses a CT scanner and a dye injected into a vein to take detailed pictures of the coronary arteries, the blood vessels that supply the heart muscle. It shows any narrowing and any fatty deposits, called plaque, in their walls.

NICE, which advises the NHS, recommends a CT coronary angiogram as the first test for many people with new chest pain that could be angina. It is also useful when you have cardiac risk factors, such as high cholesterol or a family history of heart disease, to see whether they are already causing early changes.

The first part of the scan needs no dye. It measures how much calcium has built up in the plaque in your heart arteries and gives it a number, the calcium score. The more calcium there is, the higher the risk of a heart attack. The score helps decide how firmly to treat risk factors such as high cholesterol.

The hospital will send you its own instructions, which usually ask you to:

• avoid tea, coffee, energy drinks and other caffeine the day before and on the day
• have nothing to eat for a few hours beforehand
• carry on with your usual medicines unless you are told otherwise
• leave jewellery at home and avoid clothes with zips or metal clasps

Tell the team if you have asthma, kidney problems or have ever reacted to a contrast dye, or if there is any chance you could be pregnant.

You change into a gown and small sticky pads are put on your chest to follow your heart rate. The pictures are clearest when the heart beats slowly and steadily, so you may be given a medicine to slow it, and sometimes a spray or tablet that widens the heart arteries.

You lie on a bed that moves through a ring-shaped scanner. The radiographer works the scanner from the next room but can talk to you throughout. You will be asked to keep still and to hold your breath for a few seconds at a time. When the dye goes in, you may feel warm for a moment, which passes quickly.

Afterwards you can get dressed, eat and drink as normal and go home. If you were given a medicine to help you relax, someone may need to drive you.

It is non-invasive: no tube is passed into an artery, so there are fewer complications, such as bleeding or bruising, than with a coronary angiogram. The radiation dose is low but the scan is still only done when it is needed. It is not suitable during pregnancy, and the dye may not be suitable for people with advanced kidney problems, severe asthma or an allergy to the dye.

If the scan shows narrowing and it is not clear whether it is limiting the blood flow, a further test may be suggested.