Heart Disease

Atherosclerosis

Hardening of arteries

   Tunica intima thickens with deposits of Cholesterol, Fibrous (scar) tissue, Dead muscle cells, Blood platelets        

      Arteries become less elastic and partially narrowed

        ↑BP which in turn accelerates atherosclerosis

         Leads to endothelium damage and weak walls

Mechanism

   Excess cholesterol leaks from lipoproteins (LDLs)

   Deposited on arterial walls

   Macrophages (white blood cells) are trapped within cholesterol

   Release free radicals which damage the arterial wall

   Activates blood platelets which stick to damaged areas releasing clotting factors (thromboxanes)

   Forms a plaque which may rupture to produce a thrombus

   Circulating thrombus is called an embolus

   Embolus may lodge elsewhere in the circulation (brain, heart arteries)

   NB: healthy arteries produce anti-clotting factors (prostaglandins) → don't form clots

Factors that aggravate atheroma formation / atherosclerosis:

   Hypertension (↑BP)

   Smoking (release of free radicals)

   High LDL and low HDL

   NB: they all cause endothelial damage

Aneurysm

   Weak arterial walls may burst leading to severe loss of blood (haemorrhaging)

   Brain aneurysm is called a stroke

Deep Vein Thrombosis

   Clots are formed by

   Endothelial damage (see atherosclerosis)

   Altered blood components (dehydration, too many platelets)

   Altered blood flow (stasis of veins) → this is what causes DVT

      Prolonged immobility

      Such as paralysis, long-distance flights, lying down for weeks after surgery

   Thrombus often originates in calf veins

   Inflammation of vein walls → destroys vein valves

   Causes leg pain, swelling, and redness

   Elastic support stockings required for life

   Prevented by taking aspirin or warfarin which inhibit blood clotting

Coronary Heart Disease

   Atherosclerosis causes arteries to become narrowed

      More force required to move blood through narrowed vessels

      Blood pressure increases

   Stable angina

      ↑exercise leads to ↑oxygen requirements by heart

      Narrowed arteries prevent more blood to pass through

      Shortage of blood to heart muscle causes chest pain

      Cells do not die as some blood can still pass through

      Pain only occurs during activity but not at rest

Myocardial infarction (MI)

   Coronary artery is totally blocked by a thrombus/embolus

   No blood supply to heart muscle and cells die

   Irreversible if not treated within 90min

Heart failure

   Prolonged blockage of artery causes damage to heart muscle

   ↓contractions / ↓cardiac output / ↓pressure generated / less blood leaves heart

   More blood is stored:

       on the right side of the heart → enlarged heart

       in veins → swollen legs and enlarged liver

Lifestyle

Cholesterol

  Needed for

     Vitamin D production in skin

     Sex hormone production in gonads and adrenal glands

     Making cell membranes

     Produce bile acid (salts)

  Has properties similar to fats → soft, waxy, and insoluble (difficult to remove if deposits form)

  Transported in blood from liver to tissues

  Safe transport is needed due to its insolubility

  Achieved by lipoproteins, which are soluble fatty proteins

  These are wrapped around cholesterol

  Normally, only small amounts of free cholesterol escape

LDL

   Low density lipoproteins

  Carries cholesterol from liver to tissues

  Normally, some cholesterol 'leaks' from the lipoprotein and is absorbed to build cell membranes

   Excess LDL/cholesterol → too much cholesterol leaks out and causes atherosclerosis

HDL

   High density lipoprotein

   Picks up cholesterol from arterial walls and carries it away from tissues

   Travels to liver where cholesterol is removed with bile

Smoking

↓antitoxidants (vitamins), more damage due to release of free radicals by phagocytes

Nicotine constricts arteries causing platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases BP

↑BP causes damage to blood vessel lining / endothelium / collagen

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 conc. of fibrinogen (in blood) → increased risk of clotting

↑LDL causes more cholesterol to leak out 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

Medication

Beta blockers reduce heart rate and reduce oxygen required by heart

Aspirin prevents blood clotting and thrombosis formation

ACE inhibitors stabilize plaques → prevent thrombus to break off

Statins reduce LDL and increase HDL

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

Heart by-pass graft

Leg veins and arteries from chest are used to by-pass the blocked region of the coronary artery

Involves open heart surgery

Reperfusion therapy after a myocardial infarction

Angioplasty done within 90 minutes of onset of chest pain

May prevent irreversible damage to the heart muscle

Prevention

1. Screen population for

   High BP

   High cholesterol

   Uncontrolled diabetes

   Smoking? Unhealthy diet? No exercises?

   Men over 55 and women over 65 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

    Coronary heart disease is a long-term degenerative disease, starts at birth