How is a knowledge of the structure and functioning of the heart relevant to the treatment of heart problems?

Coronary Heart Disease

What is it?

The second heart problem that I will discuss is called Coronary Heart Disease. It is probably the most heart of all the heart problems as well as the most common. Coronary Heart Disease affects 300,000 people in Britain each year and kills 160,000 people¹. For that reason it is the UK's and the developed world’s largest killer.

Coronary Artery Disease (CAD) is when a blockage or blockages occurs in the vessels, which supply the heat with blood. This is a result of arteriosclerosis or atherosclerosis more commonly known as the ‘hardening of the arteries’. This is a build up of fatty deposits, such as cholesterol, on the endothelium of arteries. This may then lead up to a large abnormal mass on the arterial wall – an atheroma. Atherosclerosis is the most likely to occur in the coronary arteries. These blockages obstruct the flow of blood to cardiac muscle, causing a thrombosis (or blood clot) and can damage the heart in numerous ways, depending on severity – this is what causes coronary heart disease.

Figures  ¹ and 1.1 taken from Human Health and Disease, Ann Fullick

Angina – it is the most common symptom of coronary heart disease. It occurs during exercise when the heart is having to work harder to supply more oxygen to our muscles. As the cardiac muscle is beating faster, more oxygen is needed – however blood flow is obstructed by the narrowing in the coronary arteries (called atherosclerosis). This results in a painful tightening of the chest, which discontinues after exercise has stopped but can be very distressing at the time. Angina can make simple exercises such as walking across a room impossible therefore severely debilitating the sufferer.

Heart Attack – scientifically known as myocardial infarction (MI), MI occurs when total closure of a coronary artery occurs because of atherosclerosis and thrombosis. This causes the death of some heart muscle as a result of lack of oxygen and other vital nutrients. The pain is very similar to that of angina but it is more severe and persistent. It continues after exercise has stopped and may even start even though there is no exertion at all. MI can be fatal in a few minutes, hours or even days if the problem is not treated early enough.

Treatment of Coronary Heart Disease

There are a variety of ways in which coronary heart disease can be treated but this depends of the severity of the disease and the patient’s health. Coronary heart disease can be treated both surgically and through the use of drugs.

Medication

• Glyceryl Trinitrate – this drug causes “rapid dilation of the blood vessels and so improves the supply of oxygen to the cardiac muscle” (Human Health and Disease, Ann Fullick, 1998). Dilation of this kind enlarges the lumen in arteries hence giving the blood more room to flow past fatty build-ups (atheroma) under less pressure. This drug provides a fast relief from the symptoms of Angina, but it does not stop MI.  
• Calcium antagonists – these “dilate arteries and arterioles by preventing calcium ions moving into the smooth muscle cells” (Human Health and Disease, Ann Fullick, 1998). Therefore there is less resistance of blood flow in the coronary arteries. Calcium antagonists are for constant use and are prescribed when a patient suffers from acute angina, making a simple walk across a room impossible. They do not work as quick dilators like Glyceryl Trinitrate does.

Surgical Treatment

• Balloon Angioplasty – scientifically known as Percutaneous Transluminal Coronary Angioplasty. This technique was pioneered in the 1970s. A catheter is inserted in to an artery in the leg and when treaded up through the body to the aorta, where it is fed down the coronary artery affected by an atherosclerosis build-up. A balloon is then inflated, compressing the build-up to the walls of the artery and allowing normal blood flow to resume This operation is fairly simple and can be done under a local anaesthetic, taking approximately 40 minutes to complete² (Heart, BBC Documentary). It is believed that angioplasty could replace “one in six” (Encarta Encyclopaedia 1998, Microsoft) coronary bypass operations.

• Heart bypass – there are four main arteries supplying the heart with blood; the left coronary artery, the right coronary artery, the left circumflex and the left anterior descending. If a 100% blockage occurs in any of these major arteries then it is often necessary to bypass it. The procedure is complicated compared to balloon angioplasty, however if successful the patient can enjoy a much increased quality of life – in many cases bypass surgery can save the patient’s life. In the procedure veins are taken from either the legs or arms and sewn to the aorta and the sewn back beyond the blockage of the affected coronary artery. Depending on how many arteries have an atherosclerosis build up, the patient may require double, triple or even quadruple bypasses to bypass all the damaged arteries.

• Heart Transplant – if the heart and cardiac muscle have become so badly damaged my MI or any other disease and no other treatment will save the patient’s life than a heart transplant is the only option available. This involves replacing the damaged heart with one from a person (who has died in an accident) or with recent developments, a pig’s heart. The procedure is itself dangerous and involves pumping the patient’s blood artificially through a machine while the new heart is attached. If the patient survives the operation then they will have to use immunosuppressive drugs for the rest of their life to stop their body from rejecting their donor heart. However these drugs reduce the patient’s immune system and can make them highly vulnerable to infections and other diseases. The operation has become more commonplace in the developed countries of the world and advances in the field have enabled people with transplants to live for up to ten to fifteen years.

• Artificial Hearts – artificial hearts provide an ideal long short term solution for those people who are in need of a transplant, and have the potential to be more successful than donor. In an article in the Guardian Newspaper it was said that, “…. Heart transplants have revolutionised the treatment of heart disease but a desperate shortage of donors means that there is still a need for an effective artificial heart” (The Guardian 2001). In its early pioneering, mechanical hearts mimicked a bionic heart with four chambers. However surgeons now realise that it is simpler to use just a single chamber pump. One of the most recent one chamber heart transplants has been Jarvik 2000 (Microsoft Encarta 1998). It is small enough to fit into the left ventricle but it can pump ten litres of blood per minute. On June 20th 2000 it was given to the first British recipient. Due to his patient’s age, a heart transplant would not have been a viable option. The operation was successful and lasted longer than some transplanted hearts.

• Pacemakers – there are many reasons why a person may require a pacemaker, sometimes because their heart is beating to slow, sometimes because their heart is beating to fast or because there is a block effecting the excitation of the heart. Through radical improvements in the medical field, pacemakers are becoming very common and effective. The procedure if fairly straight forward and takes approximately sixty minutes to implant. To begin with an incision is made and a pocket if formed overlaying the muscle on the outside of the chest wall. It is large enough to insert the pulse generator. Then the pacemaker is thread through the right subclavian vein using a fluoroscope to visualise the leads. This makes sure that the leads are in the most suitable position.

The pacemakers themselves can control the atrium by itself or both the atrium and ventricle. These are called dual chamber pacemakers and are more expensive. Many permanent pacemakers are now ‘rate responsive’ meaning that they can change the rate of the heart depending on the physiological condition so that when a person is exerting themselves e.g. in exercise, the pacemaker can increase their rate hence increasing blood flow to the cells.