Coronary heart disease

Atherosclerosis is caused by the narrowing and stiffening of the arteries due to fatty deposits, known as atheroma, accumulating in their walls.

The process that leads to atherosclerosis begins with abnormally high levels of excess fats and cholesterol in the blood. These substances infiltrate the lining of arteries at sites of microscopic damage, forming deposits known as atheroma. This can happen in any of the body's arteries, including those supplying the brain with blood, when the result may be a stroke. The atheromatous deposits gradually form raised patches known as plaques. These consist of fatty cores within the arterial wall, covered by fibrous caps. The plaques narrow the space, or lumen, within the artery and this restricts the overall flow of blood to tissues beyond the site. It also causes turbulence that disrupts the smooth flow of blood and the eddies over the plaque surface mean that blood is more likely to clot. The major risk factors for atherosclerosis include smoking, a diet high in saturated fats, lack of exercise, and excess weight.

Restricted blood flow

Atherosclerosis can occur anywhere in the main coronary arteries or their branches. However, plaque usually builds up at points where the arterial wall is subject to turbulent flow, such as where an artery divides. The branching causes natural eddies that result in damage. The arterial wall at the site often becomes thickened as new muscle cells grow into the plaque.

Atheromatous plaques

These fatty deposits gather under the inner lining of the arterial wall. They consist of a fatty core topped by a fibrous cap.

Angina, chest pains that come on with exertion and are relieved by rest, is a sign that the heart muscle is not receiving an adequate supply of blood.

Angina is caused by a temporarily inadequate supply of blood to the heart muscle, usually because of arterial narrowing due to atherosclerosis. The pain most often occurs when the heart's workload is increased, for example with exercise, and fades with rest. Other triggers for angina are stress, cold weather, or a large meal. An angina attack typically begins with a heavy, constricting pain behind the breastbone. This can spread into the throat and jaw, and down into the arms, especially the left one. The pain usually subsides within 10-15 minutes. People with angina often take medication that relieves the pain by causing the coronary arteries to widen (dilate).

Damaged heart muscle 

During angina, areas of heart muscle downstream from a narrowed artery suffer from lack of oxygen. After the attack, the muscle recovers.

Why angina occurs 

Atherosclerosis of a coronary artery causes narrowing in the vessel and a reduction in blood flow. During exertion the heart beats faster and the muscle's demand for oxygen increases. However, extra blood cannot pass through the narrowed artery and the muscle "cramps".

Angiography

The diagnostic procedure known as angiography shows the outline of blood vessels on a specialized X-ray image (called an angiogram). A fine catheter (hollow tube) is passed into an artery, usually in the leg, and then threaded up towards the heart via the aorta. A contrast medium, or radio-opaque dye, is injected into the catheter and X-ray images are viewed on a monitor. These show the dye flowing through the coronary artery network and reveal any narrowing or blockage.

A heart attack occurs when an area of cardiac muscle is deprived of blood, and therefore oxygen, due to a blockage in an artery.

A heart attack (myocardial infarction) is the result of coronary heart disease due to atherosclerosis, and the subsequent formation of a blood clot, or thrombus. Once formed, the clot can completely block blood flow to an area of heart muscle, starving it of blood and eventually causing tissue death. If possible, the blood flow must be restored to the damaged cells as quickly as possible. A heart attack usually occurs suddenly, with little or no warning. The chest pain may resemble that of angina, but it is more severe, is not necessarily brought on by exertion, and persists despite resting. A heart attack can also cause sweating, shortness of breath, nausea, and loss of consciousness.

Myocardial infarction

When a coronary artery becomes blocked, the cells of the heart muscle it supplies begin to die from the lack of oxygen and nutrients and the accumulation of poisonous waste products.

Coronary thrombosis

An area of plaque may become roughened, perhaps because its fibrous covering tears. Blood cells, especially platelets, begin to stick to the area and trigger the formation of a thrombus (clot).

Enzyme release

Degenerating muscle fibres in the affected area release a number of enzymes into the circulation. Measuring these enzymes through a blood test indicates the extent of the heart muscle damage.

Damaged heart muscle

If cells are deprived of oxygen and nutrients, they quickly degenerate. If the blood supply is not restored quickly, the tissue eventually dies, a process known as necrosis. At this stage, the damage to the cells is irreversible.

Clotted artery

The healthy lining of a blood vessel allows blood to slip over it smoothly. Blood tends to clot where this smooth flow is disturbed by projections from the vessel wall.

Thrombolytics

The key to heart attack treatment is speed. The sooner the arterial blockage can be removed, then the sooner blood flow is restored to the damaged area and it may be able to recover. Thrombolytic drugs are often introduced directly into the blood stream after a heart attack. These help to dissolve the clot that is blocking the coronary artery by increasing levels of a substance called plasminogen in the blood. Plasminogen breaks down the strands of fibrin that bind the clot together and the clot dissolves. Antiplatelet drugs are routinely given for some time after discharge from hospital, as these thin the blood and prevent further clot formation.

Angioplasty 

This procedure is used to widen a section of coronary artery that has been narrowed or blocked by atheroma. It is often carried out to treat severe angina or after a heart attack. Angioplasty may be part of the same procedure as angiography, which visualizes the coronary arteries on an X-ray. Under local anaesthetic, a fine catheter (hollow tube) is inserted into the femoral artery in the groin (or sometimes the arm), and passed up the aorta and into the coronary artery network. When the affected site is reached, a tiny balloon at the end of the catheter is inflated to widen the narrowed area. An expandable stainless steel mesh stent is often left permanently in place after withdrawal of the balloon catheter. This prevents the artery from narrowing again.