Why is coronary angiography performed?

Coronary angiography is a specialised X-ray test to find out detailed information about your heart (coronary) arteries. It is used to assess the extent and severity of any  narrowing or blockages that may be causing angina.

What is angina and what causes it?

Angina is chest discomfort that occurs when the blood supply to the muscles of the heart is restricted. It usually happens because the arteries supplying the heart become narrowed by fatty deposits called atheroma. Atheroma may gradually form inside the lining of arteries over many years (similar to water pipes that get ‘furred up’). As these fatty deposits become bigger they may cause enough narrowing of one or more of the arteries to cause symptoms. If a blockage occurs suddenly this may cause a heart attack (myocardial infarction).

Although the blood supply may be sufficient at rest, when the heart works harder, such as during exercise, it needs more blood and oxygen to work properly. If the extra blood that your heart needs cannot get past the narrowed arteries, patients experience angina.

The discomfort of angina feels like a dull, heavy or tight pain in the chest that can spread to the left arm, neck, jaw or back. The pain is usually triggered by physical activity or stress and typically only lasts for a few minutes.

What is coronary angiography?

Coronary arteries do not show up on a plain X-ray. During coronary angiography, dye is injected down the coronary arteries that show up on an X-ray ‘like a road map’. Dye is injected into the coronary arteries through a thin, flexible tube, called a catheter.  The procedure is described below.

Coronary angiography is the gold standard assessment of a patient who is suspected of experiencing angina. The set of pictures obtained during coronary angiography demonstrates where blood flows around the heart and shows the presence and severity of any coronary artery narrowing.

The images obtained allow the Cardiologist to determine the appropriate type of treatment a patient requires, whether this is medicine alone or in combination with some type of intervention. Intervention may be through either angioplasty and stenting (now called percutaneous coronary intervention or PCI, where a balloon is inserted across a narrowing and an expandable metal stent (“a mesh”) is inserted holding the coronary artery open restoring blood flow; or open heart surgery, through coronary artery bypass grafting (known as CABG).

Additional information can also be attained during the procedure, including measuring pressures in the different chambers of the heart, providing information about heart valve function and assessing how well the heart’s main pumping chamber (the left ventricle) works. This information is additive to that obtained non-invasively through cardiac ultrasound (echocardiography). Below are examples of diagnostic coronary angiographic images that demonstrate the presence of severe coronary artery disease.

Below are examples of diagnostic coronary angiographic images that demonstrate the presence of severe coronary artery disease.

How is a coronary angiography performed?

The coronary angiogram procedure is performed in a room similar to an operating theatre, called a cardiac catheter laboratory (or cath lab) and can be expected to take approximately 30-45 minutes. The cath lab is staffed by a trained team lead by a Cardiologist. The team includes a Cardiac Physiologist, who monitors the patient’s heart tracing (ECG) blood pressure, pulse and oxygen levels throughout the procedure, a Radiographer who moves the X-ray imaging equipment and two nurses who assist the Cardiologist.

The coronary angiogram is performed under local anaesthetic. A thin flexible plastic tube, a cardiac catheter, is introduced via a short introducer sheath (tube) that is placed into the femoral artery in the groin or via the radial artery in the wrist. (Fig.1) The procedure itself is not painful although patients can expect mild discomfort when local anaesthetic is injected into the skin and a sensation of pushing when the introducer tube is inserted. Thereafter the procedure is not painful. Many Cardiologists give patients intravenous sedation so they feel relaxed and conformable throughout.

After insertion of the introducer sheath, cardiac catheters are guided towards the heart guided by x-ray screening (Fig.2). You may be able to see the progress of the catheter on the X-ray monitor. Once in place a special dye, or X-ray contrast, is injected through the catheter and a series moving pictures are recorded. The contrast shows up the outline of the coronary arteries and demonstrates the presence of any abnormality such as narrowing or blockages. The tip of the catheter is then put into the other main coronary artery and the test is repeated. You cannot feel the catheter inside the blood vessels although you may feel an occasional ‘missed’ or ‘extra’ heartbeat during the procedure. During the procedure your heartbeat is monitored by electrodes placed on your chest which provide a tracing on an electrocardiograph (ECG) machine.

If there is significant narrowing the Cardiologist may proceed to treat the abnormal areas through PCI at the same sitting, although patients may be brought back to the cath lab for this to be performed on a separate occasion.

Coronary angiography is usually performed as a day-case procedure although on occasion patients are observed in hospital overnight.

How do I prepare for coronary angiography?

Before patients are admitted for coronary angiography they will have routine testing including blood tests and a heart tracing (ECG). Patients are asked not to eat any food for 6 hours before the procedure although clear fluids can be drunk until the procedure.

All medication should be taken as usual (including aspirin) although anticoagulant agents such as Warfarin will need to be stopped several days before the procedure following the explicit instructions given by the attending Cardiologist.

Diabetic patients will also be given specific advice. If they take insulin or other medication for diabetes, the timing of when to take these on the day of the test will need to be clarified.

All patients will have to sign a consent form stating they agree to the procedure being done, confirming that they understand the procedure, including possible complications (see below). If patients may be pregnant, they need to tell the doctor before consenting to do the test.

What happens after the procedure?

Once the angiogram has been completed the catheter is removed from the artery. There may be a little bleeding when the sheath is removed. If the sheath was introduced from the leg, an implantable collagen plug (called an angioseal) may be introduced to stop bleeding. This device seals the hole where the sheath was inserted and gradually dissolves over 90 days. There may be small residual swelling at the site of the angioseal. If no closure device is used a nurse will press on the site of the sheath insertion for a short while after the procedure. Patients must remain lying flat for a period of time after the angiogram.

For angiograms performed from the wrist via a radial approach, a tight air-filled pressure band, called a TR band, is placed over the artery for approximately two hours after the angiogram, with gradual release of the pressure as bleeding stops.

Most people who have an angiogram without any additional procedures can expect to go home the same day. However depending on the results and other conditions, the doctor may ask patients to stay in hospital longer. There may be residual bruising and mild tenderness where the catheter was inserted. Patients usually feel back to normal within a few days. Painkillers such as paracetamol will help to ease this.

The doctor will discuss the test results and send a letter to your GP. You will need to rest for a few hours after the test and should ask a friend or relative to accompany you home. Most people are able to resume their normal activities the next day.

Patients are advised to avoid air travel for at least one week following an angiogram, but this advice will vary depending on the angiogram results or in the presence of other medical conditions.

What are the risks of a coronary angiogram?

A Cardiologist will not recommend that a coronary angiogram is performed unless he or she feels the benefits, in terms of determining a diagnosis or the severity of your condition, outweigh the small procedural risk.

Although a coronary angiogram is the gold standard for the assessment of the presence of underlying coronary artery disease it is a minimally invasive test and thus has a small associated risk of serious complications. Coronary angiography will only be performed on the advice of a Cardiologist based on the severity of a patient’s symptoms, often guided by the results of other preliminary non-invasive cardiac assessments. Fortunately coronary angiography is a safe test and serious complications are rare.

The commonest and generally minor complication after coronary angiography is bleeding from the puncture site where the catheter was inserted; occasionally it can leave a haematoma (a raised bruise) where blood collects under the skin. There is a small risk of injury to the artery where the sheath is inserted although this is rarely clinically important in cases performed radially. The risk of bleeding is also lower for radial procedures than those performed from the groin (femoral).

Major bleeding is rare even after procedures performed from a femoral approach.  Bleeding into the pelvis may require blood transfusion and can very rarely require an interventional radiologist or surgeon to repair any damage.

Overall the risk of risk of any major complication during the procedure such as  having a heart attack, stroke, requiring emergency coronary artery bypass surgery or death. is very low, quoted as  approximately 1 in 500 procedures. The risk varies depending on your overall health and on the underlying heart condition. The risks are much lower for planned elective cases rather than when coronary angiography is performed as an emergency.

Other rare complications include heart rhythm disturbance (arrhythmia), kidney injury and allergy to the contrast agent. Any patients with reduced kidney function are treated with extra caution and given intravenous fluid and medication to reduce the small risk of kidney injury. Patients with a known contrast allergy are given anti-histamines and steroids before the procedure.