Prosthetic Heart Valves


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Prosthetic Heart Valves

  1. 1. Prosthetic Heart Valves Dr Mohamed Salih Aziz MRCP- UK
  2. 2. introduction The first mechanical prosthetic heart valve was implanted in 1952. Over the years, 30 different mechanical designs have originated worldwide. These valves have progressed from simple caged ball valves, to modern bileaflet valves.
  3. 3. Prosthetic Heart Valves In 1961, Starr and Edwards reported the first clinically successful placement of a prosthetic heart valve. Since that time, great strides in the development of new prosthetic valves (PVs) and in the surgical technique for their placement have led to improved valvular hemodynamics and durability and decreased valvular complications.
  4. 4. Prosthetic Heart Valves Types of Prosthetic Heart Valves ; (1) Mechanical (2) Bioproshetic
  5. 5. Mechanical Valves Mechanical valves have evolved over the past 30 yrs from the initial caged- ball model of Starr & Edwards to a tilting- disk design . The tilting-disk design of Bjork & Shiley and Medtronic-Hall valves improved hemodynamics flow characteristics and increased the effective orifice area EOA over the caged-ball valve .
  6. 6. Mechanical Valves
  7. 7. The caged ball design - is one of the early mechanical heart valves - It uses a small ball that is held in place by a welded metal cage. -The ball in cage design was modeled after ball valves used in industry to limit the flow of fluids to a single direction. - Natural heart valves allow blood to flow straight through the center of the valve - This property is known as central flow, which keeps the amount of work done by the heart to a minimum
  8. 8. The caged ball design  With non-central flow, the heart must work harder to compensate for the momentum lost to the change of direction of the fluid.  Caged-ball valves completely block central flow, therefore the blood requires more energy to flow around the central ball.  the ball is notorious for causing damage to blood cells due to collisions thus the pt is required to take life long anticoagulants
  9. 9. The tilting-disc valves - In the mid-1960s, a new class of prosthetic valves were designed that used a tilting disc to better mimic the natural patterns of blood flow. -The tilting-disc valves have a polymer disc held in place by two welded struts. -The titling-disc valves open at an angle of 60° and close shut completely at a rate of 70 times/minute.
  10. 10. Mechanical Valves
  11. 11. The Tilting-disc Valves -This tilting pattern provides improved central flow while still preventing backflow. -The tilting-disc valves reduce mechanical damage to blood cells. This improved flow pattern reduced blood clotting and infection. -the only problem with this design is its tendency for the outlet struts to fracture as a result of fatigue from the repeated ramming of the struts by the disc.
  12. 12. Medtronic-Hall single tilting disk valve has a Teflon sewing ring, and titanium housing machined from solid cylinder and a carbon-coated disk with flat parallel sides. The disk which opens to 75 degree in the aortic model and 70 in the mitral, is retained by an S shaped guide strut that protrudes through a hole in the center of the disk.
  13. 13. Medtronic-Hall single tilting disk valve
  14. 14. Bileaflet Valves * In 1979, a new mechanical heart valve was introduced. *These valves were known as bileaflet valves, and consisted of two semicircular leaflets that pivot on hinges. The carbon leaflets exhibit high strength and excellent biocompatibility. The leaflets swing open completely, parallel to the direction of the blood flow. *They do not close completely, which allows some backflow.
  15. 15. Bileaflet valves *Since backflow is one of the properties of defective valves, the bileaflet valves are still not ideal valves. *The bileaflet valve constitutes the majority of modern valve designs. *These valves are distinguished mainly for providing the closest approximation to central flow achieved in a natural heart valve
  16. 16. Advantages of mechanical valves; The main advantages of mechanical valves are their high durability. Mechanical heart valves are placed in young patients because they typically last for the lifetime of the patient
  17. 17. Disadvantages of mechanical valves; increased risk of blood clotting mechanical valve recipients must take anti-coagulant drugs (sodium warfarin) chronically, which effectively makes them borderline hemophiliacs.
  18. 18. PROSTHETIC TISSUE VALVES Bioproshetic heart valves are divided into: A) Heterografts( from another species) B) Allografts/Homografts( human cadever) The design of bioprosthetic valves are closer to the design of the natural valve. Bioprosthetic valves do not require long-term anticoagulats, have better hemodynamics, do not cause damage to blood cells, and do not suffer from many of the structural problems experienced by the mechanical heart valves
  19. 19. Human Tissue Valves Homografts; valves that are transplanted from another human being. Autografts; valves that are transplanted from one position to another within the same person
  20. 20. Human tissue valves A homograft is a valve that is transplanted from a deceased person to a recipient. they do not require immunosuppressive therapy. A homograft that has been donated must be cryopreserved in liquid nitrogen until it is needed. homografts tend to have good hemodynamics and good durability. it is not clear whether homografts have better hemodynamics or durability than animal tissue valves.
  21. 21. Human tissue valves Autografts are valves taken from the same patient that they are implanted into. The most common autograft procedure is the Ross procedure, which is used in patients with diseased aortic valves (The dysfunctional aortic valve is removed and the patient's pulmonic valve is then transplanted to the aortic position) A homograft pulmonic valve is usually used to replace the patient’s pulmonic valve
  22. 22. Continue Ross procedure  The Ross procedure allows the patient the advantage of receiving a living valve in the aortic position.  The long term survival and freedom from complications for patients with aortic valve disease are better with the Ross Procedure than any other type of valve replacement .  After 20 years, only 15% of patients require additional valve procedures .
  23. 23. Continue Ross procedure  In cases where a human pulmonary artery homograft is used to replace the patients’ pulmonary valve, freedom from failure has been 94% after 5 years time, and 83% at 20 years.  The tissues of the patients’ pulmonary valve have not shown a tendency to calcify, degenerate, perforate, or develop leakage
  24. 24. Animal Tissue Valves  Animal tissue valves are often referred to as heterograft or xenograft valves.  These valves are most often heart tissues recovered from animals at the time of commercial meat processing.  The leaflet valve tissue of the animals is inspected, and the highest quality leaflet tissues are then preserved.  They are then stiffened by a tanning solution .
  25. 25. Animal Tissue Valves The most commonly used animal tissues are: A) porcine, which is valve tissue from a pig B) bovine pericardial tissue, which is from a cow
  26. 26. Porcine valves  the valve tissue is sewn to a metal wire stent, often made from a cobalt-nickel alloy.  The wire is bent to form three U-shaped prongs.  A Dacron cloth sewing skirt is attached to the base of the wire stent, and then the stents themselves are also covered with cloth.  Porcine valves have good durability and usually last for ten to fifteen years
  27. 27. The Hancock II features low pressure fixation, a calcification retardant treatment and a thinner stent
  28. 28. Bovine pericardial valves  Are similar to porcine valves in design.  The major difference is the location of the small metal cylinder which joins the ends of the wire stents together.  In the case of pericardial valves, the metal cylinder is located in the middle of one of the stent post loops.  Pericardial valves have excellent hemodynamics and have durability equal to that of standard porcine valves after 10 years
  29. 29. St. Jude Toronto Stentless Porcine Valve (SPV)  It represents a recent advance in the use of heterograft valves  Are Stentless valves made by removing the entire aortic root and adjacent aorta as a block, usually from a pig.  The coronary arteries are tied off, and the entire section is trimmed and then implanted into the patient .  Reports have documented superior hemodynamics when matched with
  30. 30. LV mass index and wall thickness normalizes sooner postoperatively. Early data suggest that durability and valvular characteristics are similar to those in the homografts. If an elderly pt requires bioproshesis, the stentless heterograft valve appears to be indicated, especially in a pt with small aortic annulus.
  31. 31. Evaluation The evaluation of prosthetic valve begins with careful cardiac auscultation and understanding of normal findings for each type of valve in both the aortic and mitral positions. Mechanical valves produce high-pitched crisp valve sounds; - in tilting discs models, closure is louder than opening. - in caged-ball design opening is louder than closure
  32. 32. Continue auscultation; Bioproshetic valve sounds are similar to native valves and would be difficult to distinguish purely by auscultation. Prosthetic valves: - In the Aortic position: Ejection systolic murmur = normal finding Diastolic murmur of reg = valve dysfunction In the Mitral position: Soft diastolic rumble = normal Significant pansystolic = valve dysfunction
  33. 33. Continue auscultation; Ingeneral, a change in the intensity or quality of the valve sounds or a new changing murmur would signify abnormal valve function and warrant further evaluation.
  34. 34. Evaluation; Echocardiography Advantages; 1) determine baseline function immediately after surgery 2) Monitor performance serially over time 3) Detecting dysfunction
  35. 35. Diagram illustrating the normal pattern of regurgitant flow in the plane perpendicular to the disk. During systole, reg normally occurs at both the disk margins and at the extreme of the closure line.
  36. 36. Complications of prosthetic valves (1) thrombosis and thromboembolism (2) Structural valvular deterioration and failure (3) Endocarditis (4) Paravalvular leak
  37. 37. Prosthetic valve thrombosis - 0.1% to almost 6% per patient-year depending on the valve type, anticoagulation status, and valve position. - Thromboebolism in patients with mechanical valves has an incidence of : * 4% per patient –year eout anticoagulation. * 2% ~ ~ ~ ~ e antiplatelet ttt. * 1% ~ ~ ~ ~ e adequate warfarin ttt
  38. 38. Prosthetic valve thrombosis Risk factors for thrombosis and thrombo- embolism include: - caged-ball valves - valves in mitral position - inadequate anticoagulation. - multiple prosthetic valves - pts > 70yrs, AF, LV dysfunction
  39. 39. Adequacy of anticoagulation depends on a number of factors and should be individualized based on type of PV, age, and associated clinical risk factor for TE
  40. 40. In general, for mechanical valves INR values: * < 2.0 are inadequate. * from 2.5 to 3.5 are adequate for most newer mechanical valves. * > 3.5 are reserved for higher risk patients.
  41. 41. ASA/WARFARIN  The addition of low dose ASA to warfarin therapy reduce overall mortality, especially from major systemic embolism, but also may increases the risk of bleeding.  ASA/warfarin may best be used in high-stroke- risk pts with a newer mechanical valve and therefore a therapeutic INR of 2.5.
  42. 42. Clinical presentation of PV thrombosis  Insidious onset of fatigue and SOB  acute CV collapse . Clinical findings  Decreased PV sounds  A new murmur  Change of a previous detected murmur.
  43. 43. Echo findings of PV thrombosis  decreased movement of the disk  increased transvalvular gradient  significant valvular regurgitation  thrombus size, number, and location TEE is better able to visualize and determine the number of PV thrombi. TEE can miss anterior AV thrombi and may be inferior may be inferior for accurate Doppler measurements of transvalvular gradient
  44. 44. Treatment of PV thrombosis Heparin anticoagulation:  If the thrombus is < 5mm and nonobstructing, heparin may be all that is required.  When thrombi are > 5mm or significantly obstructing valvular flow, the pt should undergo valve replacement. Thrombolysis has been suggested as an alternative to surgery, but there is a 20% chance of cerebral embolism and a rethrombosis rate as high as 15-20%.
  45. 45. Structural Valve failure Structural valve failure is essentially confined to bioprosthetic valves with one historical exception: The Bjork-Shiley single tilting disk was withdrawn from use in 1986 after reports of strut fracture
  46. 46. Structural Valve damage (SVD)  Homograft valves, in general, last longer than heterograft.  SVD occurs more rapidly in younger pts and in pts with PVs in mitral position.  valves in mitral versus aortic position are subjected to a higher closing pressure and increased stress on the valve  reoperation for bioproshetic valve failure has significantly higher mortality ( 25-30%) than initial valve replacement.
  47. 47. Prosthetic Valve Endocarditis PVE  Incidence is 3-6%  Early PVE , occurring <60 days from valve surgery, usually results from contaminated surgical devices or a postoperative wound infection , common bacteria are staph epedermidis, staph aureus, and gram negative bacteria
  48. 48. Late PVE > 60 days  pathophsiology is similar to native valve endocarditis, common organisms are strep species.  risk factors for PVE are; -multiple valves -antecedents native valve endocarditis  signs and symptoms are similar to those in native valve endocarditis. Fever in a pt with a PV should be considered endocarditis until proved otherwise .  TEE is highly senstie and specific for the diagnosis of PVE
  49. 49. Treatment of PVE  identification of the organism - appropriate antibiotics.  valve replacement is indicated in pts with PVE when: - medical ttt fails - they developed life threatening complications - infected with virulent bacteria or fungi