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Date: 8 April 2020
Coronary artery disease
The heart is a muscular organ that pumps blood around the body. Blood contains the oxygen and food your body's organs need to function. To pump properly the heart muscle needs its own blood supply, and this is provided by vessels called the coronary arteries.
As people get older it is common for these arteries to become narrowed. This narrowing process occurs earlier in people with diabetes, high blood pressure or raised cholesterol and smokers. However, narrowing is common and may occur in people who do not have any of the above factors. If the arteries become narrowed or blocked, the blood supply to a region of heart muscle may be reduced causing the heart to contract less efficiently causing a region of the heart muscle to die.
The sensation that many people experience when their heart muscle does not receive enough blood is called angina, which is usually felt as a tight constricting feeling across the chest. This sensation may radiate to the throat or down an arm and it may be associated with feelings of breathlessness.
If a region of heart muscle dies, this is called a 'heart attack' or 'myocardial infarction'. The narrowing of the coronary arteries (also called 'coronary heart disease') causes several major problems. It causes symptoms of angina and in some people it leads to myocardial infarction which in turn can lead to heart failure or untimely death.
The British Heart Foundation estimate that over 1.85 million people living in the UK currently have or have had angina. It is estimated that coronary heart disease causes over 117,000 deaths a year in the United Kingdom, accounting for approximately one in five deaths in men and one in six deaths in women.
Treatment of narrowed coronary arteries has two aims. The first is to try to prevent the coronary arteries blocking as this may lead to myocardial infarction, causing heart failure or death. The second is to improve the blood flow to the heart to alleviate symptoms of angina.
There are three aspects to most people's treatment:
- Percutaneous coronary intervention (PCI)
- Coronary artery bypass surgery (CABG)
The above procedures are ways of improving blood flow to the heart and are called 'revascularisation procedures'. Many factors are considered to decide what is necessary and most appropriate for the individual patient.
If any of the above procedures are required a 'coronary angiogram' (x-ray) will take place to discover any narrowing or blockages.
X-ray images are made of the heart arteries and a special liquid is injected into the artery to make them visible. This can be done throughout the artery at the top of the leg or wrist and is performed under local anaesthetic. A tube (called a catheter) is then fed into the artery and guided under X-ray imaging control until the tip reaches the heart.
When the catheter is in position a special liquid is injected into the heart arteries so they appear on the x-ray machine. The position and shape of any narrowings in these arteries can then be identified. This part of the procedure is called an angiogram, and usually takes about 30mins.
The angiogram can be a day case procedure or as a prelude to a percutaneous corornary intervention (PCI), which would then occur immediately after the images are obtained.
If the clinical circumstances and the angiogram findings suggest that the blood flow to the heart is poor either of the following will take place:
- Percutaneous coronary intervention (PCI)
- Coronary artery bypass operation (CABG)
Percutaneous coronary intervention
A percutaneous coronary intervention (PCI) procedure starts like an angiogram. Once the images have been taken a thin wire is steered under x-ray image control across the narrowed part of coronary artery. A balloon is fed over this wire and tracked across the narrowing. Inflating the balloon squashes the fatty tissue and widens the artery. This may need to be done several times to be successful in fully widening the artery.
In most cases a stent is implanted which is a small stainless steel mesh in the shape of a tube which can be used to scaffold the artery wall in order to keep it open. The stent is crimped over the balloon which is used to deploy it against the inner wall of the artery. As the balloon inflates the stent expands pressing out against the arterial wall. This helps to hold open the newly widened artery. The balloon is then deflated and withdrawn, leaving the stent in place. In the last few years we have seen the development of special stents called 'drug eluting' stents, which have a drug on their surface. This drug passes into the wall of the artery it is scaffolding to try to improve the longer term success rates of the procedure.
Following a PCI, most patients return home the next day. Generally, this is a very safe form of treatment. The potential complications can be broadly split into those that occur during or shortly after angioplasty and those that occur weeks or months later.
At the time of PCI it is sometimes not possible to successfully open up the blocked vessel. Generally if the vessel was narrowed the success rates are very high, but if the vessel was completely blocked before the procedure, the chances of re-opening it are rather lower. In addition, but very rarely it is sometimes necessary to resort to emergency coronary artery bypass surgery to treat a complication. This occurred in less than 0.1 per cent of cases in 2006 in the United Kingdom.
Any treatments involving the coronary arteries may, rarely, be associated with complications such as stroke, heart attack or death (the risk is less than 1 per cent). Some patients are at higher risk of developing complications than others. For example, the treatment of a patient in a stable situation is associated with complication rates of less than 1 per cent, but in the context of an acute heart attack, this may rise to 10 per cent or more.
After PCI, the symptoms of angina are usually much improved. There follows a period when the walls of the newly stretched arteries heal. If a simple metal stent has been deployed, then over the course of the first six months cells grow over this part of the artery wall, and form a new lining, embedding the stent within the artery wall. If the healing process is over exuberant this can lead to re-narrowing of the artery, and a recurrence of angina (so called 'restenosis'). If this is going to occur it usually does so within the first six months.
If a drug eluting stent has been implanted, there is much less proliferation of cells around the stented site. This means that the chance of recurrent symptoms in the first few months is much lower. After both types of stent there is a small risk (less than 1 per cent per year) of the treated vessel blocking abruptly, usually due to clot formation. This risk is slightly higher for simple metal stents early after the angioplasty, and slightly higher for drug eluting stents later after the angioplasty.
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