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主動脈瓣移植的臨床展望

主動脈瓣移植的臨床展望

Aortic Valve Homografts A Cinical Perspective
Michael E. Staab, MD
Rick A. Nishimura, MD
Joseph A. Dearani, MD
Thomas A. Orszulak, MD

Mayo Clin Proc 1998; 73:231-238
Valve Prosthesis
Mechanical
types: caged-ball, tilting-disk, bi-leaflet
advantage: durability
limitation: thrombogenicity
Bioprosthetic
types: heterografts, homografts
advantage: short term anticoagulation
limitation: structural failure
Mechanical Valve Prosthesis
Types
caged-ball (Starr-Edwards)
tilting-disk (Medtronic-Hall)
bileaflet (St Jude)
Advantage: durability (1)
Limitation: thrombogenicity
1. N Engl J Med 1996;335:407-416
Bioprosthetic Heterografts
advantage
long term anticoagulation unnecessary (1)
limitation: structural failure
leaflet calcification & tissue degeneration leading to valvular regurgitation
stenosis is uncommon
rate of porcine valve degeneration 26% (aortic), 39% (mitral) in 10 yrs (2)
1. N Engl J Med 1993; 329:524-529
2. Ann Thorac Surg 1990; 49:370-383
Bioprosthetic Homografts
1956 - first aortic valve homograft was used in the descending thoracic aorta for aortic regurgitation
1962 - first sub-coronary use
high incidence of post-op failure *
  (years)   5 10 15 20
survival rate (%)  85 66 53 38
re-operation (%)  22 62 85 95
* Circulation 1991; 84(suppl 3):III81-III88
Bioprosthetic Homografts
early preservation techniques
formaldehyde, chlorhexidine, propiolactone, ethylene oxide, ?-irridiation, freezing at -70oC
grafts are nonviable
high incidence of cusp rupture

Bioprosthetic Homografts advances
Improving valve durability
newer preservation techniques: cryopreservation by liquid nitrogen with low-dose antibiotics
homovital grafts (fresh unpreserved)
reduced time for graft procurement
donor rather than autopsy specimens

Bioprosthetic Homografts University of Alabama
1981-1991
cryopreserved aortic grafts in 178 pts
survival rate
91% at 1 year
85% at 8 years
freedom from re-operation
95% at 8 years

J Thorac Cardiovasc Surg 1993; 106:154-165
Bioprosthetic Homografts Prince Charles Hsopital
1975-1994
cryopreserved aortic grafts in 680 pts
hospital mortality 2.8%
survival rate
77% at 10 year; 45% at 20 years
freedom from re-operation
69% at 15 years

O’Brian. Ann Thorac Surg 1996;60:S65-S70
Homovital homografts London
grafts are harvested, stored in tissue culture medium, and used in 3 days
275 grafts implanted over 13 years: 147 subcoronary, 128 aortic root
no transmission of disease reported
cumulative survival
85% at 10 yrs (94% in the aortic root gp)
freedom from re-op: 91% in 10 yrs
J Thorac Cardiovasc Surg 1995;110:186-193
Bioprosthetic Homografts implantation techniques
Freehand scalloped technique
retention of minimal donor tissue
technically challenging, require exact sizing to prevent regurgitation
Cylinder technique
retention of native aortic sinuses and sinotubular junction
requires coronary reimplantation
Ann Thorac Surg 1996;62:1069-1075
Bioprosthetic Homografts implantation techniques
Mayo Clinic series 1985-1994
implantation     scalloped   cylinder
numbers   59       78
late mod-sev AR 26%       12%
7 yr re-op rate  24.2%      11.5%
Ann Thorac Surg 1996;62:1069-1075
Bioprosthetic Homografts cylinder techniques
improved outcome
maintaining the natural valve geometry and structure
ensures better aortic cusp coaptation
reduces the risk of aortic regurgitation
Ann Thorac Surg 1996;62:1069-1075
The “Ross procedure”
A double valve procedure
transfer the patient’s native pulmonary valve into the aortic position
insert a homograft into the resected pulmonary position
long term follow-up of 131 pts
47% survival at 20 yrs (age 11 - 52)
35% re-op (15% aortic, 10% pulmonary)
Circulation 1997;96:2206-2214
Aortic Valve Homograft complications
aortic regurgitation is the major mode of graft failure
early aortic regurgitation technical factors (sizing, distortion)
late aortic regurgitation commissural malalignment, cuspal distortion, cuspal prolapse from root enlargement
cuspal deterioration is less common
Aortic Valve Homograft  endocarditis
Low incidence of endocarditis affecting homografts: 6% at 15 yrs (1)
Treatment of choice for prosthetic valve endocarditis (PVE)
mortality for PVE has been 20-50%
hospital mortality reduced to 8.3% with homografts in the treatment of PVE (2)
1. Ann Thorac Surg 1995;60:S65-S70
2. Semin Thorac Cardiovasc Surg 1997;11:53-61
Aortic Valve Homograft anticoagulation
Mechanical valves
risk of thromboembolism, major bleeding, stroke is approx 3% (1) with INR of 2.5-4.9
Aortic homografts
anticoagulation is unnecessary
1. N Engl J Med 1995; 333:11-17
Aortic Valve Homograft Conclusion
Advantage of not needing anticoagulation
Not yet a perfect valve
Aortic regurgitaiton still occurs with modern preservation techniques
structual failure also a limitation, particularly in the young patient
Aortic Valve Homograft Conclusion
In older patients (age >60), heterografts have a relatively low rate of structural failure, the advantage of homografts is minimal
Surgical expertise required; may not be available at all institutions

Aortic Valve Homograft indications
active endocarditis, particularly those with concomitant root abscess
complex aortic pathology (aneurysm or dissection) when the valve is not amenable to repair or resuspension
young patients (age <60) when long-term anticoagualtion is not desired or is contraindicated



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