Firstly, a quick biology lesson/reminder:
- Arteries generally carry oxygenated blood from the heart to the body, and veins carry the de-oxygenated blood from the various parts of the body back to the heart.
- The muscles of the heart receive their own blood supply from the coronary arteries.
- There are 2 main coronary arteries, the left and the right. The left divides into the left main and the left descending artery, and between these three arteries, the muscle of the heart is supplied with oxygenated blood.
- The coronary arteries fill mostly during the relaxation phase of the heart in contrast with the rest of the body which is dependent on the expulsion of blood via the aorta from the left chamber of the heart, the left ventricle.
If one (or more) coronary arteries starts to narrow, then the blood supply to that area of the heart supplied by that coronary will become affected and can cause damage to the underlying heart muscle. This can result in angina, ie chest pain. The narrowing of the vessels is more commonly seen in men, in late middle to late age and more often in smokers (mostly due to the deposition of plaques inside the vessel walls). Also, cholesterol can combine with fat, calcium, and other substances in the blood to form plaque. Plaque then slowly builds up and hardens in the arteries, causing them to narrow. This is termed arteriosclerosis. This build up of plaque can lead to heart disease, heart attack, and stroke.
There is also a risk that a plaque may become dislodged from the wall and obstruct the vessel further down, where the diameter of the vessel narrows. This will also cause decreased blood flow and ischaemic damage to heart muscle, eventually the heart muscle dies if it does not receive oxygenated blood. This occurs in a myocardial infarct.
The replacement of one or more of these partially occluded (blocked) vessels is termed a coronary artery bypass graft, CABG. These are commonly called heart bypass, and known as a ‘cabbage’ by Cardiac clinicians. About twenty thousand CABG’s are carried out every year in England.
The process involves taking a section of a large vein (sites that are commonly used are the chest, arm or leg veins), under general anaesthetic. The vein is sewn into the wall before and after the site of the narrowing, i.e. bypassing the blocked/occluded section of artery. If a number of coronary arteries are involved, then each of these may be by-passable, though this will depend on the location of the narrowing, and also if the width of the artery after the narrow section is a good fit for the other end of the bypassing vein.
There are risks associated with the procedure, minor ones being an irregular heart beat (this need not be sustained however), and infection at the wound site. More serious complications include a myocardial infarction (as a consequence of there being no blood beyond the narrowing or complete occlusion from plaque dislodgement from the arterial wall). Cerebrovascular events (‘strokes’) are also recognised complications.
Overall, 5 year survival rates are about 90% and this figure is continuing to improve with advances in subsequent medical treatment.
The symptoms of breathlessness, chest pain and an increased ability to take gentle exercise are often seen in a relative short period of time following surgery.
Sometimes a procedure called coronary angioplasty is used. The term 'angioplasty' means using a balloon to stretch open a narrowed or blocked artery. However, most modern angioplasty procedures also involve inserting a short wire-mesh tube, called a stent, into the artery during the procedure. The stent is left in place permanently to allow blood to flow more freely. Coronary angioplasty is sometimes known as percutaneous transluminal coronary angioplasty (PTCA). The combination of coronary angioplasty with stenting is usually referred to as percutaneous coronary intervention (PCI).
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