HEALTH ESSAY

What is Cardiovascular Disease? How may it be prevented and to what extent is heart transplant surgery a sensible solution to the problem of Coronary Heart Disease?

Cardiovascular Disease, or CVD, is Malaysia biggest killer, responsible for 40% of premature deaths in Malaysia.

CVD is a comprehensive term for several afflictions of the cardiovascular system - the heart and blood vessels of the body. These afflictions are Coronary Heart Disease (CHD), Atherosclerosis and arteriosclerosis, Angina, Coronary Thrombosis and Myocardial Infarction and Stroke.

Apart from the high mortality rate - it is estimated that CVD kills 140,000 people a year under 75 years old, chronic heart disease causes incapacitation, suffering and pain in many of it's victims. Much heart disease is also self-inflicted and therefore avoidable.

Atherosclerosis and Arteriosclerosis

The underlying cause of CHD, strokes and other diseases of the blood vessels is usually atherosclerosis. Atherosclerosis is caused by the build up of cholesterol and other fatty substances in walls of arteries. Firstly the deposits form small streaks on the endothelium of the artery, but gradually build up to form patches known as atheromatous plaques. The deposit is called an atheroma and causes the arterial walls to thicken, hence narrowing the lumen of the artery.

The onset of an atheromatous plaque may be caused by some physical damage to the artery, sometimes caused by high arterial pressure - hypertension. Smooth muscle cells proliferate at the site of damage and then lipids and cholesterol are deposited from the blood. The cholesterol deposited in the walls may be attacked by free radicals released by phagocytes which may slow down the passage of low density lipoproteins which carry cholesterol back into the blood with the result of increased deposition of cholesterol.

Atheromatous plaques roughen the lining of the artery and disturb the flow of blood, which can stimulate the formation of a clot known as a thrombus. When blood comes into contact with fatty and fibrous tissue, platelets stick to the roughened surface and release clotting factors called thromboxanes. In healthy arteries the amount of thromboxane and prostaglandin is balanced, but in damaged arteries the balance is upset because the endothelial cells lining the artery are damaged so blood clots form.

This can block the blood vessel it is forming in, or small pieces known as emboli can break off and travel through the blood vessels and jam at any narrow point in the system, causing a restriction of blood flow to the affected area.

Another process - arteriosclerosis is also associated with atherosclerosis. Arteriosclerosis is the deposition of fibrous sediments in damaged areas and calcium is also deposited, leading to calcified plaques. Fibrosis and calcification cause the artery wall to harden and loose it's elasticity. These hardened arteries are more prone to rupture and are also liable to initiate development of a thrombus, particularly if the atheroma breaks through the endothelium of the blood vessel.

The artery walls become weakened by plaque, if the weakness causes the artery to stretch the artery may rupture causing a haemorrhage known as an aneurysm.

Diagram showing how atheromatous plaques can cause a blood clot to form.

Coronary Heart Disease (CHD)

CHD, also known as Ischaemic Heart Disease (ischaema - reduction of blood supply to a tissue) is a disease of the two coronary arteries supplying the heart muscles with oxygenated blood and nutrients. CHD causes damage to these arteries by blocking the lumen of the vessels with plaques which leads to damage to the heart as it becomes deprived of oxygen therefore causing the heart tissue to become oxygen starved.

The consequence of this is that part of the heart becomes deprived of oxygen and therefore dies as it is being effectively suffocated unless an interconnecting blood vessel can take over the supply.

There are two forms of CHD - angina and myocardial infarction.

Angina

As the coronary arteries are not supplying heart muscle with a sufficient amount of volume they are respiring anaerobically. This causes a build up of lactic acid and the muscle cramps causing pain in the centre of the chest which radiates out to the neck, jaws and arms and back. Even gentle exercise such as climbing stairs or walking across a room may bring on an angina attack. Difficulty in breathing, sweating and dizziness may also occur.

Angina is a chronic disorder rather than an acute disorder, it is one of the symptoms of CHD and can be treated with vasodilators such as amyl nitrate and nitro-glycerine which cause veins to dilate, reducing the amount of blood returning to the heart therefore lowering its work load. Beta blockers have been used to block the sympathetic nervous stimulation of cells called beta-receptors in the heart and blood vessels, thus reducing the heart rate to about 60-64 bpm. The lowered rate reduces oxygen consumption of the heart by about 20%.

Coronary Thrombosis and Myocardial Infarction.

Coronary thrombosis is the blockage of a coronary artery by a thrombus. If a coronary artery becomes blocked by a thrombus or embolus, heart muscle will become starved of oxygen leading to myocardial infarction (heart attack). The area deprived of blood, hence oxygen will become damaged and die.

Severe damage to the heart results in a reduced cardiac output (less blood is pumped out in a given time) and a build up of blood in the veins increasing their blood pressure. When the heart does not pump out blood as fast as it arrives heart failure is said to occur - the heart is not working as efficiently. Infarction on the left side of the heart causes a build up of blood in the pulmonary veins, fluid leaves the blood and enters the lungs causing difficulty in breathing and poor oxygenation of blood. Infarction on the right side causes build up of blood in the veins of the body causing oedema due to back pressure on the capillaries.

Strokes

A stroke is known medically as a cerebro-vascular accident, it is a sudden interference with the circulation of arterial blood to part of the brain. A lack of oxygen to the brain will usually cause some permanent damage as the brain tissue is being starved.

There are two main types of strokes, cerebral thrombosis and cerebral haemorrhage. A blood clot may develop on a atherosclerotic deposit in a major cerebral artery, this is known as cerebral thrombosis and is the cause of about 25% of strokes. About 75% of strokes are caused by a haemorrhage of a cerebral artery which may be caused by excess blood pressure or the artery becoming weakened by atherosclerosis.

The effects of a stroke depend on the extent of damage to the brain and what areas of the brain have been damaged. As the brain is sectioned into different parts according to their function, a stroke in one area will cause a different effect on the sufferer than a stroke in another section. The brain has remarkable recovery powers and areas next to the damaged areas are able to undertake the activities of the damaged areas.

Prevention of CVD

CVD is a long term degenerative disease and people must be made aware of the complications of an unhealthy lifestyle early to try and educate them towards a healthy lifestyle. It has long been considered that CVD is a self inflicted disease because the lifestyle led by sufferers has influenced the onset of the disease.

The main risk factors that can lead to CVD are as follows:

Diet

A diet that is high in saturated fats causes a rise in blood cholesterol. In countries such as Japan where CVD is relatively rare, lower fat intakes and lower blood cholesterol are found than is typical of people in Britain. The amount of blood cholesterol is influenced mainly by the amount of saturated fats in the diet rather than the amount of cholesterol. This increases the deposition of cholesterol in the arteries leading to the formation of atheromatous plaques which are the underlying cause of CVD.

Hypertension

Hypertension, or high blood pressure, is associated with stress, smoking, obesity, excessive alcohol consumption and lack of exercise.

Long term hypertension places an extra strain on the heart and cardiovascular system making it work harder, speeds up the development of atheromatous plaques and increases the chances of suffering from angina, myocardial infarction or stroke. Hypertension may lead to heart failure, which occurs when heart muscles weaken and are unable to pump properly.

A blood pressure of 170/100 increases the chance of dying from CHD twofold compared to that of men with a normal blood pressure of 120/80.

Smoking

Smoking cigarettes has both a harmful effect on the respiratory system as the cardiovascular system.

Carbon Monoxide and nicotine are both toxic to the endothelium of arteries and therefore make the penetration of cholesterol plaques easier causing atheromatous plaques.

Carbon monoxide reacts irreversibly with haemoglobin to form carboxy-haemoglobin. This decreases the volume of oxygen carried in the blood and will therefore induce angina attacks.

Nicotine causes a higher concentration of fibrinogen which stimulates the clotting of platelets thus increasing the chance of developing a thrombus in an artery as the platelets are stimulated to stick to the surface of the endothelium.

Nicotine increases blood pressure and heart rate, but also constricts the blood vessels. This increases the chances of thrombosis especially stokes if the carotid arteries are effected as well as putting the heart under extra strain.

Atherosclerosis of peripheral arteries supplying the legs (also known as Beurger's Disease) causes crippling pain on walking and may lead to the death of tissues, subsequent gangrene which leads to amputation. More than 90% of sufferers of this condition have smoked at least 20 cigarettes a day for more than 20 years.

Physical Exercise

A lack of exercise will lead to a weak heart with a low cardiac output as the heart muscle is rarely exercised. Like any other muscle, exercise will increase the strength of the heart muscle and will enable a larger stroke volume to occur, therefore the heart doesn't need to beat as fast to pump as much blood around the body.

Lack of exercise will increase the risk of CVD because the heart is working much harder to pump blood around the body, therefore is being put under extra strain as with hypertension.

Gender

Men are twice as likely to suffer from CVD than women. Testosterone has a harmful effect on the cardiovascular system and pre-menopausal women produce oestrogen which protects against CHD. Post menopausal women tend to have an increase in blood fat levels, so the risk of developing CVD increases, but treatment with hormone replacement therapy will protect the body again from CVD. Although men cannot help their gender, to lower their risk they should make extra considerations about diet, exercise and smoking.

Stress

Leading a stressful lifestyle may increase the risk of heart attacks and angina attacks. Stressful lifestyles are also often coupled with lack of exercise (sedentary jobs in offices), smoking, excessive alcohol intake and poor diet.

Genetic factors

Heart disease has an inherited component, the more close relatives you have who develop heart disease, the more likely you are to suffer too. The main reasons that CVD runs in families is that it has a genetic component - such as certain genes that may increase the risk of developing atheromatous plaques. The second reason is that families share a common environment such as diet and being in an environment with smoke from cigarettes.

Treatment for sufferers of CVD

Heart Transplants

With organs such as the heart, transplantation is used only if the alternative to early death. Close matching organs are therefore sometimes difficult due to the urgency of obtaining the donor heart. The demand for donor hearts is very high, with an estimated 400 people per million needing a heart or heart/lung transplant.

The surgical process of heart transplantation is relatively straight forward as the heart is a simple organ. The major medical problem is that of the body rejecting the heart, although immuno-suppressant drugs curb the rejection of the heart, few recipients of a transplanted heart live longer than 5 years after the operation. This is longer than the recipient of the heart would have lived without the surgery and there is a much improved quality of life and relief from pain, fatigue and breathlessness. The Immuno-suppressive treatment also could lead to infections such as pneumonia and the growth of tumours, damage to bones and body organs occurring very easily as the immune system is not working to full standards. These drugs must be taken for the rest of the person's life.

Due to the problems however, few heart transplants are carried out, there is also a great shortage of suitable donor hearts. The use of artificial hearts and xenographs from animals such as pigs are being researched into to for future heart transplantation methods. Transplants are also very costly to the NHS and donors may not always be available.

A better method may be to repair the heart with bypass operations - an autograft, if areas of the coronary artery have become blocked with atheromatous plaques. A vein from the leg is grafted on to the heart to bypass the blocked coronary artery. As the tissue comes from the same patient there is no need for immuno-suppressive drugs as the tissue is already genetically matched.

Diagram showing bypass of diseased coronary artery

An angioplasty may also be carried out which is the mechanical widening of the lumen of an artery affected by atheromatous plaques. A deflated balloon is attached to a fine catheter and inserted into the partially blocked artery. When inflated it stretches the lumen, widening it enough to increase the flow of blood and reduce the risk of a thrombus forming.

Although these surgical methods can alleviate the symptoms of CVD, after surgery the patient must also be willing to take care of their health with a good diet, stop smoking if a smoker and gentle exercise to experience the benefits of their operation. If not the whole operation was pointless as they will damage their 'fixed' body once again and be in no better health physically.