Heart Disease

Coronary Heart Disease

• Arteries supplying the heart become narrowed and the blood supply to cardiac tissues is reduced
• Heart has to work harder to force blood through narrowed vessels / blood pressure increases
• Angina
  • Chest pain due to severe shortage of blood to the heart muscle - cells do not die
  • Pain only occurs during activity but not at rest
  • Caused by narrowing of coronary arteries (atherosclerosis)
• Heart attack (myocardial infarction)
  • When a coronary artery is totally blocked by a thrombus/embolus
  • No blood supply to heart muscle and cells die - often fatal
• Heart failure
  • Blockage leads to damage of heart muscle and to gradual weakening of muscle
  • Less efficient pumping
  • Often accumulation of blood on right side → enlargement of heart

Causes of Coronary Heart Disease

• The main cause is atherosclerosis
• Often called hardening of the arteries
• Inner layer of artery wall thickens with deposits of
  • Cholesterol
  • Fibrous (scar) tissue
  • Dead muscle cells
  • Blood platelets
• Fats, in the form of lipoproteins, accumulate beneath the endothelium
  • Form plaque on the wall of arteries, also called atheroma
  • Arteries become less elastic and partially narrowed
  • Accelerated by high blood pressure
  • Arterial endothelium damage is more likely but also leads to further weakening
• Aneurysm: weak walls may burst leading to severe loss of blood (haemorrhaging)
  • Brain aneurysm is called a stroke
• Atheroma increases the risk of blood clotting
  • Thrombus (blood clot) may break away and lodge elsewhere in the circulation (e.g. brain, heart)
  • Circulating thrombus is called an embolus

Cholesterol and Atherosclerosis

• Cholesterol has important functions and is needed for
  • Vitamin D production in skin
  • Sex hormone production in gonads and adrenal glands
  • Making cell membranes
  • Make bile acid (salts)
• Cholesterol is an alcohol, not a fat but has properties similar to fats - soft, waxy, and insoluble (difficult to remove if deposits form)
• Cholesterol is transported in the blood stream from the liver to tissues
  • Safe transport is needed due to its insolubility
  • This is achieved by lipoproteins, which are soluble fatty proteins
  • These are wrapped around the cholesterol
  • Usually, only small amounts of free cholesterol escape
• Fatty streaks adhere to wall of arteries - Atheroma/atherosclerosis/plaque forms
  • Narrows lumen of artery
  • Damages endothelium
  • Can lead to formation of thrombus/blood clot

Lipo-Proteins

Low density lipo-proteins LDL's

• Carry cholesterol from the liver to the tissues
• Normal levels: some cholesterol 'leaks' from the lipoprotein and is absorbed to build cell membranes
• High levels: too much cholesterol leaks out
  • Cholesterol is deposited on the arterial walls
  • White blood cells are trapped within the cholesterol
  • Free radicals are released by white blood cells and react with cholesterol
  • This damages artery wall which allows further cholesterol deposits (i.e. Atherosclerosis)
  • Blood platelets are activated and stick to damaged areas releasing clotting factors (thromboxanes)
  • Healthy arteries produce anti-clotting factors (prostaglandins)
  • Normally a balance between these two. Healthy vessels do not form clots

High density lipo-protein HDL's

• Carry cholesterol away from tissues, including artery walls
• Travels to liver, is broken down and removed with bile

Smoking

• Reduces levels of antitoxidants (vitamins), more damage due to release of free radials by phagocytes
• Nicotine constricts arteries causes platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases blood pressure [EXAM]
• Raises conc. of fibrinogen (in blood) → increased risk of clotting
• Higher blood pressure causes damage to blood vessel lining/endothelium/collagen [EXAM]
  • Leads to rise on blood platelets and makes them more sticky/form a plug/adhere to collagen fibres
  • Release of thromboplastin/thrombokinase
  • Fibrinogen converted to insoluble fibrin
  • Platelet plug trapped by fibrin mesh
• Raises blood cholesterol by causing a rise in LDLs in blood
• Carbon monoxide reduces the efficiency of the blood in terms of carrying oxygen
  • Haemoglobin combines with CO more readily than with oxygen → forms carboxyheamoglobin
  • Associated with plaque formation
• Principle CHD = heart muscle receives inadequate amount of blood or oxygen/(coronary) blood supply reduced

Treatment

• Lower blood pressure
  • Drugs which regulate heart rate/beat - prevent abnormal rhythms (beta blockers)
  • Drugs which prevent blood clotting making thrombosis less likely (warfarin)
• Heart by-pass
  • Vein from the leg is used to by-pass the blocked region of the coronary artery
  • Involves open heart surgery
• Angioplasty
  • Deflated balloon-like device is passed up to the heart via the aorta
  • Guided into damaged coronary artery and inflated to stretch the artery
• Transplant
  • Need to find a suitable donor
  • Need to prevent rejection → drugs that suppress immune system needed for rest of life

Prevention is more cost effective then treatment

• 1. Screen the population for
  • High blood pressure
  • High cholesterol
  • Stop smoking, healthier diet, more exercises
  • Men over 35 are at highest risk
• 2. Monitor the behaviour of the heart during exercise
  • Difficult but encouraging the population to adopt a more healthy lifestyle from an early age is important
  • Often leads to changes in diet and weight management
• 3. Giving up smoking and reducing alcohol intake
  • Reduces blood pressure
  • Many people do not heed the advice until it is too late
  • Coronary heart disease is a long-term degenerative disease, starts at birth