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. 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.
6. 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 .
8. 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
9. 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
10. 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.
12. 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.
13. 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.
15. 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.
16. 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
17.
18. 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
19. 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.
20. 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
21. 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
22. 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.
23. 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
24. 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 .
25. 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
26.
27. 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 .
28. 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
29. 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
30.
31. The Hancock II features low pressure fixation,
a calcification retardant treatment and a
thinner stent
32. 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
33.
34. 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
35. 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.
36. 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
37. 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
38.
39. 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.
44. 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.
45.
46. Complications of prosthetic valves
(1) thrombosis and thromboembolism
(2) Structural valvular deterioration and
failure
(3) Endocarditis
(4) Paravalvular leak
47. 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
48. 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
49. 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
50. 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.
51. 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.
52. 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.
53. 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
54.
55. 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%.
56. 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
57.
58.
59.
60.
61. 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.
62. 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
63. 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
64.
65.
66.
67. 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
