Ischaemic heart disease
Ischaemic heart disease (IHD) is the disease process that causes angina and heart attacks. The word ‘ischaemic’ simply means reduction in blood supply, which is what happens to the heart muscle when the coronary arteries narrow. IHD is the biggest single cause of death in the United Kingdom, killing nearly 250,000 people every year. The UK has one of the highest death rates in the world from this condition.
Fortunately, there have been many recent advances in both primary prevention of IHD, and the treatment of existing disease by drugs and non-surgical intervention. The resulting effect is that fewer people should require surgery for this condition in the future.
WHAT GOES WRONG
Most people who need heart surgery have ischaemic heart disease that has developed as a result of atherosclerosis, which causes narrowing of the coronary arteries. This process is often referred to as ‘furring up’ of the arteries in an analogy to the way water pipes fur up. You will often hear doctors refer to the narrowing as a ‘stenosis’. It is a slow, progressive process, whereby fatty deposits build up on the inner wall of the arteries. As these deposits (or ‘plaques’) enlarge, the artery narrows, and the normally smooth inner wall is also disrupted. This disruption, as well as the tendency of the plaques to crack, can cause a blood clot (thrombosis) to form.
Usually, atherosclerosis develops slowly over many years without causing any symptoms, but there are several things that may speed up the process. If a thrombosis occurs, it usually causes a sudden complete blockage of an already narrowed artery, and the person has an acute heart attack, also called a myocardial infarction (MI). You will find a more detailed explanation of
all this in the Family Doctor publication Understanding Angina & Heart Attacks.
Exactly what symptoms any one person experiences will depend to an extent on the effects of the atherosclerotic disease, but they can be very variable in any case. The narrowing in the artery may be able to supply the volume of blood required by the heart muscles (ventricles) at rest.
However, during exercise, when the heart needs extra oxygen to fuel the extra work that it has to do, the narrowing may not allow enough blood to get through. This creates an area of heart muscle beyond the narrowing that can’t work as efficiently because it is starved of oxygen. This is known as an ischaemic area.
The effects of oxygen shortage on the heart are similar to those of muscular cramp, which is also the result of a muscle getting insufficient oxygen. In this case, the pain takes the form of angina and results from oxygen starvation of the myocardial cells. As with cramp, oxygen starvation also affects the muscle’s ability to continue working, but how much the heart muscle function is reduced will depend on which part of the artery is narrowed and in how many places. If there is only one narrowing, and it is quite a long way down the coronary artery, then only a very small part of the heart will be affected, and there will be very little noticeable effect overall.
On the other hand, if there are several narrowings, and they are much nearer the beginning (or origin) of the coronary arteries, then a much larger area of heart muscle will be affected, and the person will be much more likely to get symptoms.
Narrowing near the origin of the vessel is known as proximal disease, and is much more common than narrowing near the end (distal disease). Proximal disease is obviously much more serious in its implications, particularly when it affects the very beginning of the left coronary artery, called the left main stem. If the left main stem blocks off, sudden death is almost certain because the main part of the heart will be starved of blood. For this reason, people who have been shown to have a tight narrowing of the left main stem are often kept in hospital for an operation on the next available operating list. Even in the absence of symptoms, it is serious enough to require urgent surgery, and it is not safe to put such patients on a routine waiting list.
The nature and seriousness of a person’s symptoms are related to the amount of muscle function that has been lost. They might include angina, a heart attack and/or heart failure, depending on the degree of damage. Again, all this is explained in more detail in the Family Doctor publication Understanding Angina & Heart Attacks.
