1.
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When should the surgeon
recommend the use of an aortic homograft for aortic valve replacement?
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| Adult patients with persistent native valve or prosthetic valve
endocarditis involving the aortic valve usually require aortic valve replacement as part
of their medical care. Homograft aortic valve replacement has been shown to have a
decreased incidence of recurrent bacterial endocarditis in patients with native valve or
prosthetic valve endocarditis. For this reason, many surgeons believe that in patients
with aortic valve endocarditis the replacement of choice is the aortic homograft.
Recently, young patients requiring aortic valve replacement for endocarditis have been
successfully treated with a Ross Operation. This appears to have a similar incidence of
recurrent endocarditis and the pulmonary autograft valve replacement, a viable valve, may
not require replacement or reoperation. Patients with a small aortic annulus can have
aortic valve replacement without annular enlargement using an aortic homograft or a Ross
Operation as these valves do not downsize the aortic annulus.
Patients with a medical contraindication to anticoagulation or a strong personal desire
to avoid anticoagulation (female patient of child bearing age, etc.) may be candidates for
a homograft valve rather than a mechanical prosthesis.
Patients with periprosthetic insufficiency and evidence of dehiscense of the prosthetic
aortic annulus and the native aortic annulus can be managed with aortic homograft root
replacement of the prosthetic valve. This is particularly effective in patients who have
developed valve insufficiency on more than one occasion.
Patients requiring replacement of their ascending aorta and aortic valve associated
ascending aortic aneurysm and aortic valve disease are candidates for homograft aortic
valve replacement. |
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2.
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What is the preferred
technique for implantation of an aortic homograft?
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| Aortic homografts can be inserted as a scalloped sub-coronary implant,
an inclusion cylinder or as a root replacement. Recently, many surgeons with extensive
experience with homograft aortic valve replacement have recommended root replacement for
all homograft aortic valve replacement. The free-standing root replacement is less likely
to be distorted at the time of implantation, sizing to the host aortic annulus is less
critical, the technique is familiar to most cardiac surgeons (Bentall Procedure) and
reoperation on the homograft root replacement has not been a major difficulty. |
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3.
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Should an aortic homograft
be used to replace the aortic valve and ascending aorta in a patient with Marfan's
Syndrome or annulo-aortic ectasia?
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| Replacement of the ascending aorta and aortic valve with an aortic
homograft in patients with Marfan's Syndrome or in patients with annulo-aortic ectasia can
be accomplished as a root replacement with reduction of the size of the aortic annulus t o
the size of the available aortic homograft and fixation of the size of the aortic annulus
with an external cuff of Dacron. This technique is applicable in young patients and in
patients for whom anticoagulation should be avoided. |
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4.
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Should a pulmonary
homograft valve be used to replace the aortic valve?
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| Replacement of the aortic valve with a pulmonary homograft valve has
been performed by a number of surgeons with good short-term results. The allograft
pulmonary valve leaflet has similar radial and longitudinal stress characteristics to the
allograft aortic valve leaflet. The pulmonary artery or root has very dissimilar
characteristics to those of the aorta or aortic root and therefore use of the pulmonary
allograft root as a replacement of the aortic root is not recommended. Our early, limited,
short-term experience with pulmonary homograft replacement of the aortic valve and root
was not satisfactory and has been subsequently avoided. |
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5.
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How does one
"size" an aortic homograft and does insertion technique affect size selection?
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| The size selection of an aortic homograft becomes more important in
patients for whom an intra-aortic implant is to be utilized. The measured aortic annulus
diameter, as measured with a valve sizer or by echocardiography, is the internal diameter
of the aortic annulus and represents the diameter of the aortic annulus of the homograft,
and when the homograft is implanted as an intra-aortic implant, the wall of the homograft
will occupy some of the aortic annulus diameter. In general, after proper preparation, the
aortic homograft wall will occupy 3 to 4 mm of the aortic annulus diameter at insertion.
Therefore, the aortic homograft should be 3 to 4 mm smaller than the measured aortic
annulus (i.e., a 20 mm aortic homograft would be appropriate for a 24 mm aortic annulus).
When an aortic homograft root replacement is used, the aortic homograft should be the same
size as the measured annulus or within 1 or 2 mm of the size of the aortic annulus (i.e.,
a 22 to 26 mm aortic homograft can be used to replace the aortic root with a 24 mm aortic
annulus). In patients with significant dilatation of the aortic annulus from aortic
insufficiency or in patients with annulo-aortic ectasia, the aortic annulus can be reduced
to the size that is appropriate for the body surface area of the patient and an
appropriate sized aortic homograft can be utilized after the reduction annuloplasty. |
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6.
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What are the expected late
results with homograft aortic valve replacement?
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| O'Brein and his colleagues have recently reported their results with
cryopreserved aortic valve replacement of the aortic valve (Ann Thorac Surg
1995;60:S878-91). The operative mortality for 146 aortic root replacements was 1.7%.
Patient survival was 85% and actuarial freedom from structural deterioration of the
allograft valve was 86% + at 8 years. Actuarial freedom from structural deterioration of
534 cryopreserved non-root replacement aortic allograft valves was 77% at 18 years. This
is the largest series that has been reported with long-term results of cryopreserved
allograft aortic valve replacements. Comparison of the root replacements and the
intra-aortic implants at 8 years has shown no statistical difference, although possible
advantages of the root replacement may be demonstrated with longer follow-up. |
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