CT angiography and catheter angiography: which one, and why

"Angiography" means imaging the blood vessels. Two quite different examinations share the name, and patients are often sent for one while expecting the other. The difference matters, because one is a scan and the other is a procedure.

The two examinations

CT angiography is a scan. Contrast dye is injected into a vein in your arm, the CT scanner takes images as it passes through the vessels, and a three-dimensional map of the arteries is reconstructed. Nothing enters an artery. It takes minutes, you go home the same day, and it is reported by a radiologist.

Catheter angiography is a procedure. A fine catheter is passed into an artery — usually at the wrist or groin — and contrast is injected directly into the vessel being studied, with live X-ray imaging. It is performed in the angiography unit by a cardiologist.

Why one and not the other

CT angiography answers the question "is there a problem, and where?" without entering an artery. It is the usual first step when the suspicion is moderate, and a normal result is very reassuring.

Catheter angiography answers the same question with more detail — and, crucially, it can treat in the same session. If a narrowed coronary artery is found, it can be opened with a balloon and a stent placed immediately, without a second procedure. That is why chest pain with a high suspicion of coronary disease usually goes straight to the catheter, not to the scanner.

The decision belongs to your cardiologist, and it depends on your symptoms, your risk factors, your kidney function and what earlier tests have shown. Neither examination is "better" in the abstract.

What usually comes first

Angiography is rarely the first test. Before it, most patients have some combination of an ECG, an echocardiogram, an exercise stress test, a 24-hour ECG (Holter) recording or 24-hour blood pressure monitoring. All of these are available here, and they often answer the question without any contrast dye at all — or they sharpen it, so that the angiogram is asked for the right reason.

CT angiography at Medinova

We perform CT angiography of the coronary arteries with three-dimensional reconstruction, and of the carotid arteries, the brain, the pulmonary arteries, the thoracic and abdominal aorta, the renal vessels and the arteries of the arms and legs — including dynamic (timed) aortic studies, CT venography of a single region, and mapping of the left atrium and pulmonary veins.

Coronary CT angiography

This is the scan version of a coronary angiogram: the arteries of the heart are imaged from a vein in the arm, with no catheter. It suits people with chest pain of uncertain cause and a low-to-moderate likelihood of coronary disease, where the aim is to rule out significant narrowing. A clear scan is a strong result and usually ends the investigation there.

Two things make it different from other CT scans. Your heart rate needs to be slow and steady, so you may be given a beta blocker tablet beforehand and asked to avoid caffeine that morning; and you will be asked to hold your breath for a few seconds while the images are taken. Sublingual nitrate spray is often given to widen the arteries. If the scan shows a narrowing that needs treating, a catheter angiogram is the next step — the scan itself cannot treat.

The left atrium and pulmonary vein study is a different job: it maps the anatomy of the upper heart chambers before an ablation for atrial fibrillation, so the electrophysiologist knows the layout in advance.

How to prepare

• Fasting for four to six hours is usually asked for contrast studies.
• A recent kidney function blood test (creatinine) is needed, because contrast is cleared by the kidneys.
• Tell us about diabetes medication — particularly metformin — kidney disease, asthma, thyroid disease, and any previous reaction to contrast dye.
• Tell us if you are or might be pregnant.
• For a coronary scan, avoid caffeine on the day and bring your regular heart medication with you.
• Drink plenty of water afterwards unless you have been told to restrict fluids.

A warm flush through the body as the contrast is injected is normal and passes in seconds.

Catheter angiography at Medinova

Our angiography unit performs selective coronary angiography — with ventriculography, aortography or a bypass graft check where these are needed — and treats what it finds in the same session with balloon angioplasty and stenting. Where a narrowing is borderline, its significance can be measured directly during the procedure with a pressure or Doppler wire rather than judged by eye. Right and left heart catheterisation, cardiac output measurement and pulmonary vascular reactivity testing are performed for patients whose problem is the pressure in the heart and lungs rather than the coronary arteries.

Beyond the heart, the same unit performs selective carotid, renal, brachial and lower-limb angiography, percutaneous angioplasty of these vessels, atherectomy, and intravascular stent placement in the supra-aortic and visceral arteries.

Access is usually through the wrist, which allows you to sit up and walk sooner than the groin route. You are awake, under local anaesthetic, and a diagnostic procedure typically takes twenty to forty minutes; longer if treatment is carried out at the same time. Afterwards you rest for a period that depends on the access site, and you are usually discharged the same day or the next morning. Cardiology and cardiovascular surgery are in the same building, which matters if a finding needs to be discussed between them.

When the problem is rhythm, not blood supply

Not every heart complaint is a blocked artery. Palpitations, blackouts and a pulse that is too slow or too fast are questions about the heart's electrical system, and they are answered in the same unit by different means: an electrophysiology study, which maps the abnormal circuit and can then destroy it with ablation; and the implantation, replacement or revision of permanent pacemakers, including dual-chamber devices, and of implantable defibrillators (ICDs) where the risk is a dangerous rhythm rather than a slow one. A temporary transvenous pacing wire can be placed when the need is urgent.

Children and newborns

Diagnostic cardiac catheterisation for congenital heart disease is performed here, including in newborns and in children under two, with or without coronary angiography as the case requires. These are planned procedures with their own preparation, and the paediatric cardiologist will go through it with you separately.

Risks

Both use iodinated contrast, which can cause allergic reaction — usually mild — and can temporarily affect kidney function in people who already have kidney disease. Both use X-rays; the dose is justified against the information gained, and is not a reason to avoid a test your doctor considers necessary.

Catheter angiography additionally carries the risks of entering an artery: bruising or bleeding at the puncture site, damage to the vessel, and, rarely, stroke or heart attack. These risks are small, and they are the reason the procedure is reserved for situations where the information — or the treatment it allows — is worth them.

Questions worth asking

• Which of the two am I being sent for, and why that one?
• What will change in my treatment depending on the result?
• Is my kidney function safe for contrast, and has it been checked recently?
• If a narrowing is found during catheter angiography, will it be treated in the same session?
• Which of my current medicines should I stop, and when should I restart them?

Chest pain that comes on with exertion, spreads to the arm or jaw, or comes with breathlessness or cold sweat is not something to investigate by appointment. Go to the emergency department or call 112.

CT angiography at Medinova is performed within our Radiology department and reported by our own radiologists. Catheter angiography, coronary stenting, electrophysiology, pacemaker and ICD implantation and peripheral vascular interventions are performed by our Cardiology department in the hospital's angiography unit, with Cardiovascular Surgery in the same building.