Coronary angiography, also called cardiac catheterisation, is a sophisticated test undertaken by an interventional cardiologist as a day case in hospital, which allows the doctor to obtain detailed information about the coronary arteries, and the extent and severity of any disease within them (the image to the right shows a picture taken during a coronary angiogram, demonstrating the arteries supplying the left ventricle with blood).
A coronary angiogram is considered to be the “gold standard” for documenting the coronary anatomy, and the findings will help to determine the best type of treatment for a patient with coronary artery disease, i.e. medication, angioplasty or bypass surgery.
who needs a coronary angiogram?
There are very specific scenarios in which a coronary angiogram might be undertaken, for example:
- As part of a procedure called primary angioplasty, or primary PCI, at the time of a heart attack;
- Following the result of a non-invasive test such as a perfusion MRI scan or stress echocardiogram, which suggests that the blood supply to the heart is inadequate with stress (known medically as inducible ischaemia);
- As part of the work-up for a heart valve operation;
- If a patient has symptoms suggestive of severe coronary artery disease, such as pain in the chest, jaw, neck, or left arm, particularly with exertion (angina).
What happens during the angiogram?
A patient undergoing coronary angiography will be admitted to hospital as a day case and asked not to eat or drink for 6 hours prior to the procedure. The patient lies on a table in the cardiac catheter lab, which looks similar to an operating theatre, and an X-ray machine is mounted above and moves around to take pictures.
The doctor injects some local anaesthetic into the skin above the blood vessel in the wrist or groin to numb the area. A short tube (catheter) is then inserted through a 3mm cut in the skin into the blood vessel in the wrist or groin, and through this short tube different shaped catheters are passed to the heart and to the coronary arteries.
X-rays are used to monitor the progress of the catheter, which is positioned at the origin of the coronary arteries to determine whether or not there are any narrowings.
Blood vessels do not show up on normal X-rays and so a contrast medium (dye) is injected through the catheter to visualise these.
It can sometimes be difficult to determine whether or not a narrowing in an artery is causing limitation to blood flow simply by looking at angiogram pictures, particularly in cases where the stenosis severity (degree of blockage) is in the region of 50 to 70%. The doctor may therefore also perform a pressure wire study to evaluate a suspect lesion in more detail.
A pressure wire has a sensor at the tip, and it is passed down beyond the lesion. To maximise blood flow through the artery, an injection of a drug such as adenosine is given, and the pressure wire is then pulled back across the lesion and the pressures are recorded through the vessel. The doctor then calculates the fractional flow reserve (FFR), which is the ratio of maximum blood flow beyond a suspect lesion to normal maximum blood flow in the vessel. Doctors tend to consider intervening on a lesion with an FFR of 0.8 or lower. There is also a slightly different technique a doctor can use which does not require adenosine for assessing the narrowing.
Angiogram images essentially give a side view of the vessels which can sometimes over or underestimate the severity of a narrowing. There are special catheters which act as mini ultrasound probes and allow the doctor to look more closely at the nature and distribution of the disease within a vessel, known as intravascular ultrasound (IVUS). There is also a method of imaging called intracoronary optical coherence tomography (OCT), which gives additional information about the disease severity and helps to optimise any intervention.
At the end of the procedure the catheter is removed and pressure is applied to the cut in the wrist/groin, and occasionally a plug-like device called an Angio-Seal may be inserted in the groin to stop the bleeding. The patient will most likely be sent home on the same day after a couple of hours of observation, but should avoid any strenuous activity for a few days afterwards if the catheter was inserted through the groin.
What are the risks?
Any procedure on the heart carries risks, which have to be balanced against the benefits. Risks vary depending on many factors individual to the patient, including age, presence of other medical problems such as diabetes, previous stroke, and kidney damage. The most common side-effect is bruising and some discomfort at the site of catheter entry, which is generally mild and short-lived.
Serious risks are rare, approximately 1 in 1000, but if they occur they can be potentially life-threatening. Complications include damage at the site of arterial access, bleeding, heart attack, impairment of kidney function (although this is rare in patients with normal kidney function), allergic reaction to the dye, stroke, emergency heart surgery and death.
However, it is important to remember that the procedure will be carried out in a fully equipped cardiac catheter lab, with a cardiology team (doctor, nurses, radiographer and cardiac technician) with all the equipment necessary should there be a problem.
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