CT coronary angiogram vs invasive angiogram

Both tests show whether the coronary arteries, which supply the heart muscle, are narrowed. A CT coronary angiogram (CTCA) images the arteries from outside, using X-rays and contrast injected into an arm vein. An invasive coronary angiogram passes a catheter through an artery to the heart, injects contrast directly, and films the vessels as it fills.

In short, CT is for finding out whether you have a problem, and invasive angiography is for confirming and treating one. That one distinction explains most clinical choices between them.

For CT, you may be given a medicine to slow the heart rate, then lie on the scanner while contrast is injected and a short scan is taken. You go home the same day with no wound.

For invasive angiography, local anaesthetic is used at the wrist or groin, a catheter is guided to the coronary openings, and contrast shows the vessels on live X-ray. If a significant narrowing is found and appropriate, an angioplasty and stent may be done during the same visit. A short recovery period follows to protect the puncture site.

NICE recommends that people with typical or atypical angina, and some with non-anginal pain who have specific ECG changes, are offered CT coronary angiography first (CG95). The reasoning is that most people with chest pain do not have a blockage that needs a stent, so a safe non-invasive test avoids unnecessary catheter procedures.

Invasive angiography takes over when the picture is more urgent or more likely to need treatment: a heart attack, unstable symptoms, a very high pre-test probability, or when CT shows a significant narrowing and treatment decisions need further detail.

• Stable chest pain and no known heart disease: CT is usually the first step.

• Known coronary disease with worsening symptoms, or an abnormal result on other testing: invasive angiography may be more direct.

• Suspected heart attack: invasive angiography, as an urgent pathway through hospital emergency services (call 999).

• Heavy calcium, fast irregular heart rhythm or inability to hold your breath: CT image quality may be poor and an alternative test chosen.

• Poor kidney function or contrast allergy: either test needs planning, and alternative functional tests may be considered.

A CT angiogram is not a lesser option for those who "can't have the real thing". It is the recommended first test for many patients and is more accurate at ruling disease out than most stress tests. And an invasive angiogram is not always a prelude to a stent; many people leave with medication only.

Another misconception is that CT calcium scoring and CT angiography are the same. A calcium score estimates calcium load in the arteries but does not show narrowings the way angiography does.

• Is my symptom pattern likely to need a stent, or is the aim to exclude disease?

• Will beta-blocker or nitrate be needed before CT, and are there reasons I might not tolerate them?

• If the CT shows a narrowing, what is the next step and how quickly?

• Which access route (wrist or groin) would be used for the invasive test?