Congenital and acquired valvular heart diseases often require surgical intervention. It is well known that conservative surgery by valve repair gives better long-term results. However if satisfactory repair is not possible valve will have to be replaced. In that case one has to choose the ideal valve based on the age, sex of the patient, necessity and problems of lil'elong anticoagulation. Conlplications of prosthetic valves and those associated with anticoagulation have to be taken into account while making a choice.Prosthetic valves are prone to endocarditis and patients will need prophylactic antibiotics.
Types of Valves
Prostlletic Valves
a) Starr-Edward (S-E) Silastic Ball Valve Prostltesis
This was introduced in 1961 by Albert S t m and has different models for mitral and aortic positions. It is a cage and ball valve with the cage made of stellite alloy and ball 111ade of silicoll rubber containing barium sulphate. The haenlodynarnics of any mechanical valve depends on the effective orifice area (EOA). Starr-Edward (S-E) has one of the lowest effcctive orifice areas (EOA). These valves need life long anticoagulation and antibiotic prophylaxis against prosthetic valve endocarditis.Mechanical failure is unreported.
b) St. Jrtde Medical Valve (SJM)
This is a low profile bi-leaflet valve, which was introduced in 1977. The leaflets and the housing are made of pyrolitic carbon. The currently available models are rotatable after valve is sutured and fixed. This helps to achieve unobstructed opening and closing of the leaflets in aortic and mitral positions. Two relatively high velocity regurgitation jets (seen in echocardiography) allow 10 per cent regurgitation, preventing blood stasis and thrombosis at the pivots. Anti coagulation and prophylaxis against prosthetic endocarditis are Mechanical failure is uncommon.
c) Medtronic-Hall Valve
This is a low proiile central tilting disc valve. The disc is lnade of pyrolitic carbon and housing is single piece of machined titanium.Introduced in 1977, this is one of the first rotatable valves. Afkr sutures are tied-off, valve can be rotated to the ideal position without obstruction of the disc. Allticoagulation and prophylaxis against endocarditis are mandatory. Mechanical failures have not been reported.
d) Carbomcdics Valve
Almost similar to StJude Medical valve, h i s is a low profile bileaflet valve made of pyrolitic carbon. On echo cardiography four small jets of regurgitant jets can be seen. It is also fully rotatable after fixation.Like other prosthetic valves, life long anticoagulation and prophylaxis against endocarditis are recommended. Mechanical failure is uncommon.
e)Bjork-Slziley Valve (B-S)
This is one of the earliest types of tilting disc valves introduced in early 70's. The earlier models like concavo-convex disc valves were withdrawn cardiovascular Surgery from market because of mechanical failure. The monostrut B-S valve was introduced in 1982. It has a pyrolitic carbon disc and cage made of cobalt-chromium alloy. The disc opens to 70". Anticoagulation and endocarditis prophylaxis are mandatory. Mechanical failure is not reported. This valve is rarely used now.
f)Omni Science Valve
This is another type of tilting disc valve available from 1978. The cage is made of titanium and disc out of pyrolitic carbon. There have been a few cases of mechanical failures.
Chitra Valve
This valve was designed and developed at Sri.Chitra Institute of Medical Sciences in Thiruvananthapurarn and marketed by TTK Industries. It is a tilting disc valve. The occluder (disc) is made of ultra high inolecular weight poly ethelene (UHMWPE). The housing (cage) is made of Haynes-25 alloy. Haemodynamics of the valve are excellent and even though the disc is not rigid, mechanical failures have not been reported.Like all other prosthetic valves, anticoagulation and endocarditis prophylaxis are required.
Biological Valves
Biological valves are available for all positions. For mitral position they are usually mounted on a stent (stent mounted) whereas for aortic position they may be stentless or stented. The different varieties that have been tried are allograft (homograft) aortic valves, xenograft (procine or bovine) aortic valves,pericardial, fascia lata or durarnater valves. The latter two types have been discontinued because of slructural failure.
a)Carpentier -Edwards Valve (C-E)
This is porcine aortic valve preserved in gluteraldehyde and mounted on flexible stent made of cobalt-chromium-nickel alloy (ELGILOY). Gluteraldehyde, a chemical used for tanning of leather causes stability to valve leaflets due to cross linkage of collagen fibres and it reduces antigenicity. It has sewing ring with polytetra fluoro ethylene (PTFE-Goretex), incorporating silicon rubber. Valves are available for aortic and mitral position in various sizes. Biological deterioration will occur after 7-10 years but mechanical failure is uncommon. The rate of biological deterioration 'is faster in children.
b)Medtronic Hancock (Standard Model)
These are gluteraldehyde preserved xenograft aortic valve, which are mounted. The modified orifice version (M-0) is one where the right coronary cusp (which in a porcine valve has a muscular ridge) is excised and replaced with another leaflet of a valve of the same size. A new variety of second generation Hancock valve in which the fixation pressure is zero and toludine blue is added to inhibit calcium deposition is now available.
C)Pericardiul Valves:
Types of Valves
Prostlletic Valves
a) Starr-Edward (S-E) Silastic Ball Valve Prostltesis
This was introduced in 1961 by Albert S t m and has different models for mitral and aortic positions. It is a cage and ball valve with the cage made of stellite alloy and ball 111ade of silicoll rubber containing barium sulphate. The haenlodynarnics of any mechanical valve depends on the effective orifice area (EOA). Starr-Edward (S-E) has one of the lowest effcctive orifice areas (EOA). These valves need life long anticoagulation and antibiotic prophylaxis against prosthetic valve endocarditis.Mechanical failure is unreported.
b) St. Jrtde Medical Valve (SJM)
This is a low profile bi-leaflet valve, which was introduced in 1977. The leaflets and the housing are made of pyrolitic carbon. The currently available models are rotatable after valve is sutured and fixed. This helps to achieve unobstructed opening and closing of the leaflets in aortic and mitral positions. Two relatively high velocity regurgitation jets (seen in echocardiography) allow 10 per cent regurgitation, preventing blood stasis and thrombosis at the pivots. Anti coagulation and prophylaxis against prosthetic endocarditis are Mechanical failure is uncommon.
c) Medtronic-Hall Valve
This is a low proiile central tilting disc valve. The disc is lnade of pyrolitic carbon and housing is single piece of machined titanium.Introduced in 1977, this is one of the first rotatable valves. Afkr sutures are tied-off, valve can be rotated to the ideal position without obstruction of the disc. Allticoagulation and prophylaxis against endocarditis are mandatory. Mechanical failures have not been reported.
d) Carbomcdics Valve
Almost similar to StJude Medical valve, h i s is a low profile bileaflet valve made of pyrolitic carbon. On echo cardiography four small jets of regurgitant jets can be seen. It is also fully rotatable after fixation.Like other prosthetic valves, life long anticoagulation and prophylaxis against endocarditis are recommended. Mechanical failure is uncommon.
e)Bjork-Slziley Valve (B-S)
This is one of the earliest types of tilting disc valves introduced in early 70's. The earlier models like concavo-convex disc valves were withdrawn cardiovascular Surgery from market because of mechanical failure. The monostrut B-S valve was introduced in 1982. It has a pyrolitic carbon disc and cage made of cobalt-chromium alloy. The disc opens to 70". Anticoagulation and endocarditis prophylaxis are mandatory. Mechanical failure is not reported. This valve is rarely used now.
f)Omni Science Valve
This is another type of tilting disc valve available from 1978. The cage is made of titanium and disc out of pyrolitic carbon. There have been a few cases of mechanical failures.
Chitra Valve
This valve was designed and developed at Sri.Chitra Institute of Medical Sciences in Thiruvananthapurarn and marketed by TTK Industries. It is a tilting disc valve. The occluder (disc) is made of ultra high inolecular weight poly ethelene (UHMWPE). The housing (cage) is made of Haynes-25 alloy. Haemodynamics of the valve are excellent and even though the disc is not rigid, mechanical failures have not been reported.Like all other prosthetic valves, anticoagulation and endocarditis prophylaxis are required.
Biological Valves
Biological valves are available for all positions. For mitral position they are usually mounted on a stent (stent mounted) whereas for aortic position they may be stentless or stented. The different varieties that have been tried are allograft (homograft) aortic valves, xenograft (procine or bovine) aortic valves,pericardial, fascia lata or durarnater valves. The latter two types have been discontinued because of slructural failure.
a)Carpentier -Edwards Valve (C-E)
This is porcine aortic valve preserved in gluteraldehyde and mounted on flexible stent made of cobalt-chromium-nickel alloy (ELGILOY). Gluteraldehyde, a chemical used for tanning of leather causes stability to valve leaflets due to cross linkage of collagen fibres and it reduces antigenicity. It has sewing ring with polytetra fluoro ethylene (PTFE-Goretex), incorporating silicon rubber. Valves are available for aortic and mitral position in various sizes. Biological deterioration will occur after 7-10 years but mechanical failure is uncommon. The rate of biological deterioration 'is faster in children.
b)Medtronic Hancock (Standard Model)
These are gluteraldehyde preserved xenograft aortic valve, which are mounted. The modified orifice version (M-0) is one where the right coronary cusp (which in a porcine valve has a muscular ridge) is excised and replaced with another leaflet of a valve of the same size. A new variety of second generation Hancock valve in which the fixation pressure is zero and toludine blue is added to inhibit calcium deposition is now available.
C)Pericardiul Valves:
Carpentier Edwards (Perimount Valve) I Pericardium preserved in gluteraldehyde and mounted on flexible stent is available for rnitral and aortic positions. (Perimount) C-E aortic valves have been tested for longer period and are considered to be the best among stent mounted bio-prosthetic valves.
d)Stentless Devices
A bioprosthesis mounted on a stent reduces the effective orifice area (EOA). The newer version (third generation) stentless gluteraldehyde preserved porcine valves are now available for clinical use. The comnonly used one is Toronto stentless prosthetic valve (SPV) made by St. Jude Medical. The other type is Medtronic free style porcine bioprosthesis. Both are preserved in gluteraldehyde. It can be iinplanted in the sub-coronary position in the aorta or as a full aortic root replacement with reiinplantation of corollary arteries. Usually thc cusps remain free of' calciuin at six years and 85 per cent have freedom from structural deterioration at the end of nine years.
e)Aortic Allograft (Hornograf)
In the earlier years fresh antibiotic preserved aortic allografts were tried.As the shelf life is limited, availability of all sizes at all times could not bc guaranteed. At present cryopseservation is prererred. The valve is harvested under sterile conditions and is frozen i~sing liquid nitrogc~i i n tissue culture ~nediuin contailling 10 per cent dimethyl sulpl~oxicie (DMSO). It is stored a1 -180°C. They are durable sund frcc from structural deterioration in 80 per cent of the patients at 15 ycars.
Y~ltrzorzary Autograft and Ross Procedztre
f)Sir Donald Ross in 1967 introduced the concept of using patient's own pulmonary valve (autograft) lor aortic valve rcplacen~ent and a pulnloniuy allograft to replace thc excised pulmonary valve. This cryopreservetl pulmonary allograft does not deteriorate in the low-pressure puln~onary circulation. The pullnonary :tulograSi in aortic position has fi~nctionecl well over a long period of follow-up.
g)Mitial Valve Rephceine~zt with Allograft (Mitral Honzograjt) C. Acar and collertgucs uscd mitral allograft for rnitrnl valvc replacement using a new tcchniquc of fixation of papillary musclcs. They also inserted an annuloplasty ring along with lhc cryopreservcd initral vnlvc. This complcx procedure is yet to be universally accepted.
Haemodynamics
The type of' valves chosen should have excelle~it haen~odyuamics. In studies at rest and on exercise the valve sl~ould produce only acceptable diastolic gradients in the mitral position and systolic gradient in the aortic position.This will depend mainly on the erfective orifice area (EOA) of the particular valve.
Prosthetic Valve Haemadyna~nics
d)Stentless Devices
A bioprosthesis mounted on a stent reduces the effective orifice area (EOA). The newer version (third generation) stentless gluteraldehyde preserved porcine valves are now available for clinical use. The comnonly used one is Toronto stentless prosthetic valve (SPV) made by St. Jude Medical. The other type is Medtronic free style porcine bioprosthesis. Both are preserved in gluteraldehyde. It can be iinplanted in the sub-coronary position in the aorta or as a full aortic root replacement with reiinplantation of corollary arteries. Usually thc cusps remain free of' calciuin at six years and 85 per cent have freedom from structural deterioration at the end of nine years.
e)Aortic Allograft (Hornograf)
In the earlier years fresh antibiotic preserved aortic allografts were tried.As the shelf life is limited, availability of all sizes at all times could not bc guaranteed. At present cryopseservation is prererred. The valve is harvested under sterile conditions and is frozen i~sing liquid nitrogc~i i n tissue culture ~nediuin contailling 10 per cent dimethyl sulpl~oxicie (DMSO). It is stored a1 -180°C. They are durable sund frcc from structural deterioration in 80 per cent of the patients at 15 ycars.
Y~ltrzorzary Autograft and Ross Procedztre
f)Sir Donald Ross in 1967 introduced the concept of using patient's own pulmonary valve (autograft) lor aortic valve rcplacen~ent and a pulnloniuy allograft to replace thc excised pulmonary valve. This cryopreservetl pulmonary allograft does not deteriorate in the low-pressure puln~onary circulation. The pullnonary :tulograSi in aortic position has fi~nctionecl well over a long period of follow-up.
g)Mitial Valve Rephceine~zt with Allograft (Mitral Honzograjt) C. Acar and collertgucs uscd mitral allograft for rnitrnl valvc replacement using a new tcchniquc of fixation of papillary musclcs. They also inserted an annuloplasty ring along with lhc cryopreservcd initral vnlvc. This complcx procedure is yet to be universally accepted.
Haemodynamics
The type of' valves chosen should have excelle~it haen~odyuamics. In studies at rest and on exercise the valve sl~ould produce only acceptable diastolic gradients in the mitral position and systolic gradient in the aortic position.This will depend mainly on the erfective orifice area (EOA) of the particular valve.
Prosthetic Valve Haemadyna~nics
A high profile valve like Starr-Edward may cause problems if not properly used. In rnitral stenosis with small left ventricle such a valve is better avoided.Similarly when the ascending aoita is narrow it has to be enlarged to accommodate a Stm-Edward valve.
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