Heart Valves

Heart Valves

1. Stenosis- can't open properly

2. regurgitation : won't close properly

3. causes of valve defects

   • Rheumatic fever
     • major cause of valve defects
     • side effect of common bacterial infections
     • tissue damage and scaring of heart valves
   • infective endocartitis
     • bacterial infection in blood affects valves
     • immune response leads to local damage and scarring
     • may occur after infection during surgery
   • Calcific degeneration
     • imbalance in body chemistry leads to build up of calcium on aortic or mitral valves= causes them to thicken

4. Valve repair

   • Decalcification
     • remove calcium build up from leaflets, enables them to close properly
   • reshaping
     • cut out a section of a leaflet, sew back together, valve can close properly
   • commissurotomy
     • if leaflets are thick or stuck together, surgeon opens valve by cutting points where leaflets meet

5. Mechanical heart valves

   • first = ball and cage
     • mimicked industrial valves
       • not good design, didn't mimic heart valve
       • didn't allow central flow
         • diversion around ball caused momentum change, heart must do more work
         • high does of anti coagulants
     • first one 1955, died, ball came out of cage
   • Starr-Edwards valve
     • first long term valve
       • still ball and cage
     • nine commandments
       • embolism prevention
       • durability
       • ease/security of attachment
       • preservation of surrounding tissue
       • reduction of turbulence
       • reduction of blood trauma
       • reduction of noise
       • use of materials compatible with blood
       • development of methods of storage and sterilisation
   • Tilting disc design
     • 1960's, improved central flow
       • outlet struts under cyclic stress, fatigue failure = escape of disc = death
     • Bjork-Shiley
       • tilting disc
       • disc = pyrolytic carbon, sewing ring = teflon, cage = Haynes 25
       • 82,000 implanted, fatigue failure = death, taken out of use
   • Bi-leaflet valve
     • good central flow
       • design close to bicuspid and tricuspid
         • seen in majority of modern valves
       • closure is not perfect, therefore mimics regurgitation
   • Materials
     • research = materials that do not cause clotting
     • not got a valve that wont induce coagulation
     • common materials
       • stainless steel alloys
       • molybdenum alloys
       • pyrolytic carbon for valves housing + leaflets
       • Polyester (Dacron) for sewing rings
   • advantages
     • high durability
     • placed in young children as they last lifetime of patient
   • disadvantage
     • risk of blood clotting
       • heart attack / stroke
       • must take anticoagulants
         • borderline haemophiliacs
         • also cause birth defects
           • unsuitable for woman wanting children
   • don't need replacement surgery

6. Animal tissue valves

   • common tissue
     • Pig = porcine
     • cow= bovine
   • advantages
     • do not need anticoagulants
     • inexpensive, mass produced
   • disadvantage
     • uncertain durability
     • valves break down even faster in children/ young adults
       • often used in elderly patients

7. angioplasty and stents

   • narrowing of arteries, restricts blood flow = pressure UP
   • angioplasty = extends arterial walls mechanically
     • balloon is deflated, inserted along catheter, inflated near narrowing
       • stretches artery, narrowing wall as radius extends
       • wall thinning reduces strength, so put in a stent