PROSTHETIC VALVES

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SEMINAR ON PROSTHETIC VALVES

Transcript of PROSTHETIC VALVES

  1. 1. DEFINITION Prosthetic heart valve is a device implanted in the heart of a patient with valvular heart disease. - Brunner & Suddarths (2012)
  2. 2. A surgical implant used to replace an abnormal heart valve. Most prosthetic valves require open heart surgery. The implanted valves can be porcine (from a pig) or mechanical (man-made). Also known as porcine heart valve, heart graft, mechanical heart valve. - Jose Vega (2010)
  3. 3. ANATOMY & PHYSIOLOGY OF HEART
  4. 4. HEART VALVES
  5. 5. TYPES OF PROSTHETIC VALVES
  6. 6. MECHANICAL VALVES CAGED BALL:- The first artificial heart valve was the caged-ball, which utilizes a metal cage to house a silicone elastomer ball. When blood pressure in the chamber of the heart exceeds that of the pressure on the outside of the chamber the ball is pushed against the cage and allows blood to flow. At the completion of the heart's contraction, the pressure inside the chamber drops and is lower than beyond the valve, so the ball moves back against the base of the valve forming a seal.
  7. 7. Advantages Oldest prosthetic valve. Durabilty upto 40 yr Disadvantages High profile Hemolysis High thrombogenecity Poor hemodynamics in small sizes Unique features Occluder travels completely out of the orifice, reduces thrombus & pannus growing from the sewing ring. Continuously changing points of contact of the ball reduces the wear & tear in any one area Thrombogenic risk 4-6% per year.
  8. 8. TILTING DISC VALVE Tilting disk valves have a single circular occluder controlled by a metal strut. They are made of a metal ring covered by an Eptfe fabric, into which the suture threads are stitched in order to hold the valve in place. The metal ring holds, by means of two metal supports, a disc which opens and closes as the heart pumps blood through the valve. The disc is usually made of an extremely hard carbon material (pyrolytic carbon), in order to allow the valve to function for years without wearing out.
  9. 9. Advantages Low profile Good hemodynamics even in small sizes Excellent durability Permit central laminar flow. Disadvantages Anticoagulation mandatory Higher risk of thrombosis than cage ball Sudden catastrophic valve thrombosis.
  10. 10. BILEAFLET VALVES They have two semicircular leaflets retained within the ring by hinges. The potential for impeded leaflet movement due to interference with cardiac structures is slim, as the open leaflets are positioned in the middle of the blood stream and enclosed within the ring in the closed position. Bileaflet valves are the most protected as the leaflets hardly protrude from the valve ring, even during maximum opening.
  11. 11. Advantages:- Low bulk - flat profile. Less thrombogenicy. Central laminar flow. Two semicircular discs that pivot between open and closed positions. No need for supporting struts. Good hemodynamics even in small sizes. 2 lateral, 1 central minor orifice , no chance of sudden catastro thrombosis. Disadvantages:- Anticoagulation mandatory risk of thrombosis.
  12. 12. TISSUE (BIOLOGICAL) HEART VALVES Tissue valves (also called biologic or bioprosthetic valves) are made of human or animal tissue. Some valves may have some artificial parts to help give the valve support and to aid placement. Once the tissue is removed from the animal, it is chemically treated to preserve the tissue and prevent immulogic reactions once it is placed in a patient. There are three types of tissue valves: pig tissue (porcine), cow tissue (bovine), and human (allografts or homografts).
  13. 13. Porcine Stented valves The porcine stented valve was the first generation of porcine tissue valves. They have been available for more than 30 years. The valves are made from natural porcine aortic valves, but may be used for aortic or mitral valve replacement. They are trimmed and then fixed in buffered glutaraldehyde at high pressure.
  14. 14. Porcine stentless valve The porcine stentless valve is used for aortic valve replacement. The valve is made from a natural porcine aortic valve and is fixed in buffered glutaraldehyde solution at a low pressure. No stents or synthetic sewing rings are used. Therefore, these valves are very similar to the homograft valve (see below). These valves are technically more difficult to implant but are useful in patients with small hypertrophied hearts.
  15. 15. Pericardial valves The Carpentier-Edwards PERIMOUNT Pericardial Bioprosthesis Pericardial valves include the Perimount series valves (Edwards LifeSciences). Ionescu-Shiley pericardial valves have been discontinued. More recently, stentless porcine valves have been used. They offer improved hemodynamics with a decreased transvalvular pressure gradient when compared with older stented models.
  16. 16. Other types of biological valves Xenografts are tissue valves (eg, bioprostheses, heterografts); most are from pigs (porcine), but valves from cows (bovine) may also be used. Their viability is 7 to 10 years. They do not generate thrombi, thereby eliminating the need for longterm anticoagulation.
  17. 17. Homografts, or allografts (ie, human valves), are obtained from cadaver tissue donations. The aortic valve and a portion of the aorta or the pulmonic valve and a portion of the pulmonary artery are harvested and stored cryogenically. Homografts are not always available and are very expensive.
  18. 18. Autografts (ie, autologous valves) are obtained by excising the p atients own pulmonic valve and a portion of the pulmonary artery for use as the aortic valve. Anticoagulation is unnecessary because the valve is the patients own tissue and is not thrombogenic. The autograft is an alternative for children (it may grow as the child grows), women of childbearing age, young adults, patients with a history of peptic ulcer disease, and those who cannot tolerate anticoagulation.
  19. 19. Radiologic Identification Starr-Edwards caged ball valve : Radiopaque base ring Radiopaque cage Three struts for the aortic valve; 4 struts for the mitral or tricuspid valve
  20. 20. Cinefluoroscopy: Structural integrity Motion of the disc or poppet Excessive tilt ("rocking") of the base ring - partial dehiscence of the valve Aortic valve prosthesis
  21. 21. Fluoroscopy of a normally functioning CarboMedics bileaflet prosthesis in mitral position A=opening angle B=closing angle
  22. 22. MRI: Not useful in assessing prosthetic-valve structure Used only when prosthetic-valve regurgitation or para valvular leakage is suspected but not adequately visualized by echocardiography
  23. 23. Cardiac Catheterization: Measure the transvalvular pressure gradient, from which the EOA can be calculated Can visualize and quantify valvular or paravalvular regurgitation
  24. 24. Echocardiography of Stentless Aortic Homografts Doppler flow characteristics similar to native valve. Only 2-D evidence: Increased Echo intensity, and Thickness of aortic annulus.
  25. 25. Valve dysfunction complication example Role of echo Primary mechanical failure Ball variance Strut fracture Visualize structure, assess gradient & regurgitation Nonstructural dysfunction Pt- prosthesis mismatch pannus Gradient, visualize tissue in & around the sewing ring Bleeding event Intracranial hge Source of embolus, presence & mobility of masses Endocarditis Vegetation, abcess, dehiscence Visualize area around the sewing ring, echo dense / lucent area, perivalvular regurgitation Thrombosis Thrombus impedes opening &closing of occluder mechanism Localize mass, assess gradient, detect regurgitation Embolism stroke Identify & characterize the source of emboli
  26. 26. Patient-prosthesis mismatch When the effective prosthetic valve area, after insertion into the patient less than that of a normal valve (Rahimtoola in 1978) EOA indexed to BSA is less than 0.85 cm2/m2 EOA (echo) differs from geometric orifice area (measured directly) EOA for each prostheses type & size obtained in literature from pts normally functioning prostheses Average if > 1 value -- mild (0.9 - 1 cm /m -- moderate (0.6 - 0.9 cm2/m -- severe (iEOA < 0.6cm/m (Rahimtoola)
  27. 27. Three-step algorithm Step 1: Calculation of the patient BSA. Step 2: Reference to the specific table for identification of the adequate valvular EOA according to the patient BSA. Step 3: Selection of the most appropriate type and size of valve prosthesis according to the target iEOA
  28. 28. Valve thrombosis Incidence of 0.1 to 5.7 % per patient/year 10.0 with bleeding)
  29. 33. Paravalvular Regurgitation Mild or moderate paravalvular leakage - asymptomatic , may have only a mild hemolytic anemia - can be observed carefully with serial echo Severe paravalvular leakage - usually have symptoms of heart failure or severe anemia - should be treated with surgical repair or replacement of the valve