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Description  |
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BACKGROUND
1. Field of the Invention
The present invention relates to an improved heart valve prosthesis for use
in improving the function of the mitral and/or tricuspid heart valves.
2. The Prior Art
The bicuspid or mitral valve is located in the left atrioventricular
opening of the heart. It is encircled by a dense fibrous ring and consists
of two valve leaflets of unequal size. The larger valve leaflet (called
ventral or anterior cusp) is placed adjacent the aortic opening. The
smaller leaflet is the dorsal or posterior cusp. The leaflets are composed
of strong fibrous tissue which is thick in the central part but thin and
translucent near the margin. The valves are constructed so as to pass
blood unidirectionally from the left atrium to the left ventricle of the
heart.
The tricuspid valve is located in the right atrioventricular opening and
comprises three leaflets sometimes referred to as the anterior, posterior
and septal cusps. The leaflets are roughly triangular in shape and
attached to a fibrous ring with the apices projecting into the ventricular
cavity.
Both the mitral and tricuspid valves are intended to prevent regurgitation
of blood from the ventricle into the atrium when the ventricle contracts.
In order to withstand the substantial back pressure and prevent
regurgitation of blood into the atrium during the ventricular contraction,
the cusps are held in place by delicate but strong fibrous cords which
anchor the valve cusps to the muscular wall of the heart.
In some well recognized instances of heart disease, however, valve leaflet
prolapse is evident. Prolapse of the valve leaflet appears to result from
a dilatation or elongation of the posterior two-thirds of the valve
annulus. A number of circumstances may cause the valve defect. The result
of the defect, however, is the failure of normal apposition of the
leaflets. When the leaflets fail to close completely during ventricular
systole, the leaflets become damaged, the cords ruptured and the
atrioventricular annulus distended. The result of the valve prolapse is a
syndrome often associated with chest pain, cardiac arrythmias, dyspnea,
and other adverse clinical symptoms.
One obvious solution to a serious valve prolapse is total valve
replacement. It is generally agreed, however, that total valve replacement
is too radical except in the most advanced cases. Accordingly, treatment
of valve prolapse by techniques of annuloplasty have become more
commonplace.
One of the more common annuloplastic techniques is schematically
illustrated in FIG. 1 of the drawing and consists of suturing (plicating)
the two valve leaflets together at the commissures so as to reduce the
size of the opening through which blood can pass. The purpose of this
suture is to draw the anterior and posterior cusps sufficiently close
together that normal apposition will occur during ventricular systole.
Experience has proved, however, that plication of the annulus at the
commissures places extreme stress on the tissue adjacent the sutures with
the unfortunate result that the sutures tear from the tissue damaging the
leaflets and recreating the conditions susceptible to prolapse.
A valve prosthesis for mitigating the serious valve insufficiency described
above is suggested by Carpentier in the Journal of Thoracic and
Cardiovascular Surgery Volume 61, No. 1, January 1971. The prior art valve
prosthesis described therein consists of a rigid circular or oval ring
covered with a Teflon fabric which permits the ring to be sutured in
place. The Carpentier ring was an improvement in many respects over
earlier techniques. However, two inherent disadvantages in the Carpentier
ring have become apparent. First, in order to secure the ring in place,
suture placement is required along the anterior section of the annulus
adjacent the aortic valve. Not infrequently, sutures are inadvertently
passed into the aortic valve so as to interfere with the valve function.
Moreover, to secure the rigid structure adjacent the largest (anterior)
leaflet has the effect of interfering with mitral valve function. Second,
with the passage of time sutures used for securing prior art prostheses
may be subject to degeneration as a result of continual heart and valve
action. Suture degeneration can result in separation of the prosthesis
from its secured position causing at least partial failure of the
prosthesis and risking interference with valve function.
Accordingly, it would be a significant improvement in the art to provide a
heart valve prosthesis which restores valve function without interfering
with adjacent valves and which would promote tissue adherence through
natural fibroblastic growth and endothelization through natural processes
so as to maintain the prosthesis securely in place. Such an improvement is
disclosed and claimed herein.
BRIEF SUMMARY AND OBJECTS OF THE INVENTION
The present invention comprises a uniquely shaped open ring valve
prosthesis having a special velour exterior for effecting mitral and
tricuspid annuloplasty and for overcoming valve incompetence. The surface
of the valve promotes a surprising degree of tissue infiltration and
adherence.
It is, therefore, a primary object of the present invention to provide an
improved heart valve prosthesis.
It is another valuable object of the present invention to provide a valve
prosthesis for the mitral and tricuspid valves which are configurated in
the form of an open ring.
Another important object of the present invention is to provide a heart
valve prosthesis having an exterior coating of velour fabric.
Another object of the present invention is to provide an open ring mitral
valve prosthesis constructed to leave at least the anterior valve
completely without rigid support while at the same time contracting the
valve annulus in the vicinity of the posterior leaflet and valve
commissures.
Another object of the present invention is to provide a tricuspid valve
prosthesis configurated as an open ring, the open portion of the ring
being constructed to leave most of the posterior leaflet mobile while
securing the tricuspid valve annulus.
These and other objects and features of the present invention will become
more fully apparent from the following description and appended claims
taken in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic illustration of the prior art technique of effecting
annuloplasty through plication of annulus at the commissures.
FIG. 2 is a presently preferred mitral valve prosthesis embodiment.
FIG. 3 is a cross section taken along lines 3--3 of FIG. 2.
FIG. 4 is a schematic illustration of a presently preferred tricuspid valve
prosthesis.
FIG. 5 is a cross section taken along lines 5--5 of FIG. 4.
FIG. 6 is an illustration of the mode of implantation of the mitral valve
embodiment of FIG. 2.
FIG. 7 is a schematic illustration of the mitral valve embodiment of FIG. 2
sutured in place upon a mitral valve.
FIG. 8 is a graphical illustration of the surprisingly improved tissue
adhesion effected through the use of the double velour fabric utilized by
the prosthesis embodiments of this invention.
FIG. 9 is a schematic plan view of a flexible valve prosthesis embodiment,
the broken line portion representing the configuration into which the
prosthesis will be bent upon securement to the mitral valve annulus.
FIG. 10 is a schematic cross-sectional view of the embodiment of FIG. 9 in
a state of partial disassembly to reveal interior construction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention, as represented by the presently preferred
embodiments disclosed herein, provide a valve collar prosthesis which
restores valve competence and at the same time promotes a surprising
degree of fibroblastic growth and endotheliazation to assure that the
prosthesis will remain in place and continue its function even if the
sutures should degenerate over time.
Referring now to FIG. 1, a schematic illustration of one widely recognized
prior art technique for valve annuloplasty is illustrated. In FIG. 1, a
mitral valve generally designated 12 is illustrated. The mitral valve has
an anterior leaflet 14 and a smaller posterior leaflet 16. For
convenience, the left atrium 18 is illustrated schematically.
At the commissures 20 and 22, the leaflets 14 and 16 are secured together
with sutures 24 for the purpose of reducing the enlarged opening between
the leaflets 14 and 16. It is the stretched and enlarged opening between
the leaflets which permits prolapse of the valve under pressure from the
blood. Unfortunately, however, the sutures 24 tend to tear from the
delicate tissue forming the leaflets 14 and 16 under the significant back
pressure exerted by the blood.
In accordance with the present invention, one preferred embodiment of which
is illustrated in FIG. 2, an open ring valve prosthesis generally
designated 26 can be used to effect annuloplasty of a distended mitral
valve. Referring now more particularly to FIG. 2, it will be observed that
the valve prosthesis is shaped as an open ring having an elongated central
member 28 and integral, coplanar ends 30 and 32 which are bent each toward
the other. As shown best in FIG. 3, the prosthesis 26 preferably includes
a spine comprising comparatively stiff interior rod 34, preferably formed
of metal such as titanium. Clearly, other suitable stiff or semirigid
materials could be used to form rod 34. The exterior of the rod 34 is
encapsulated in a sheath 36 of double velour fabric. The term "double
velour" fabric, as used herein means fabric having a velour nap on both
front and back surfaces. The ends of the double velour fabric are joined
together and project laterally away from the rod 34 to form an appendage
38 of fabric. While any suitable velour fabric could be used, a double
velour knitted material formed of Dacron polyester has been found highly
effective.
The velour fabric has two significant advantages. First, it provides a
convenient medium through which suture can be placed to secure the
prosthesis 26 to the surrounding fibrous tissue. Second, the velour fabric
has been found surprisingly effective in encouraging endotheliazation. In
order to adequately fill the desirable criteria for a valve prosthesis,
the encapsulating fabric should be strong, durable and biocompatible and
at the same time permit long term healing and incorporation into
sorrounding tissues. The "velour" construction has tiny loops of polyester
fabric presenting a soft surface with high pile and more pliable
consistency which facilitates passage of the suture. Notably, the velour
surface of the fabric is present entirely around the rod 34 to permit
tissue infiltration from any direction. It was determined that the double
velour fabric exhibited surprising resistance to separation from the
infiltrated tissue (adventitia). These surprising results were evidenced
in part by laboratory investigations comparing double velour, warp knitted
fabric and woven Dacron fabric of the low porosity type (see FIG. 8).
In conducting the investigations, anesthetized dogs were intubated
endotracheally for respiratory support and the abdominal aorta was exposed
by a midline laparotomy. The aorta from just below the renal arteries to
the trifurcation was removed and replaced by grafts of the double velour,
knitted and woven types. Anastomoses were made with 5-0 polypropylene
continuous sutures. The peritoneum was closed over the graft and the
abdominal incision was repaired. Intramuscular streptomycin was given for
prophylaxis against infection. The dogs were well attended, fed and
exercised during the ensuing six weeks and then sacrificed.
The grafts were opened longitudinally and examined. Peel tests were
performed using a modified Instron tensile strength testing device to
ascertain the degree of adherence of the three graft types to the
surrounding external tissue. The results of the investigation are
illustrated in FIG. 8. The double velour fabric proved to be strikingly
more adherent to the surrounding tissue demonstrating more than ten times
the force of adherence of the non-double velour fabrics. It is believed
that the profound adherence of the double velour grafts to surrounding
tissue is the result of rapid fibrous tissue infiltration.
Insertion of the mitral valve prosthesis, as will be understood by persons
skilled in the art, is performed by using a standard midline sternotomy.
Temporary cardiopulmonary bypass with hemodilution is employed and the
mitral valve is exposed through an incision medial to the right pulmonary
veins. The distance between the peripheral extent of the commissures or
the actual width of the anterior leaflet is measured or estimated and a
prosthesis 26 of appropriate size is selected. Typical of adequate sizes
for the prosthesis 26 would include 25, 30, and 35 millimeters maximum
diameter.
The prosthesis 26 is positioned such that the anterior leaflet 12 of the
mitral valve is situated in the free zone between the ends 30 and 32 of
the prosthesis 26. As shown best in FIG. 6, mattress sutures are
symmetrically placed around the prosthesis 26 and through the fabric 36 to
maintain proper spacing. A double-needle suture of braided 2-0 polyester
is used with a Teflon felt pledget 40 attached individually to the ends of
the suture 42.
Use of alternating colored sutures facilitates identification and
separation of the suture for tying. The sutures are placed carefully into
the fibrous portion 44 of the annulus but not deeply enough to encircle or
injure the underlying circumflex branch of the left coronary artery or the
coronary sinus. When all of the sutures are tied, the distended annulus is
constricted to its normal size and the mitral valve has renewed competence
with free action of the anterior leaflet 14. FIG. 7 illustrates the
prosthesis in its fully implanted position.
Another valve prosthesis embodiment generally designated 50 is illustrated
in FIGS. 4 and 5. This collar ring prosthesis 50 has a configuration which
differs from the configuration of the embodiment of FIG. 2 primarily to
accommodate annuloplasty of a tricuspid valve. The prosthesis 50 has an
enlarged coplanar ascending portion 52 which turns inwardly at 54 and
terminates at end 56. The opposite end 58 traverses a slight bend which,
by contrast to the embodiment of FIG. 2, is significantly less than the
angle traversed by the end 56. The prosthesis 50, as shown in FIG. 5, has
a spine comprising an interior rod 60 which is circumscribed by a velour
fabric 62. The rod 60 is preferably formed of titanium metal, however, any
suitable biocompatible stiff or semirigid material could be used. The ends
of the fabric are joined together to form an appendage 64. Thus, the
entire exterior surface of the prosthesis 50 is covered with velour
fabric. Preferably the velour fabric is a double velour having nap on both
sides thereof.
The tricuspid prosthesis 50 is secured in essentially the same manner as
that described in connection with FIG. 6. In the prosthesis 50, however,
the ends 56 and 58 are positioned on either side of the posterior or
septal leaflet such that the septal leaflet is situated in the free zone
between ends 56 and 58 of prosthesis 50. As with the mitral valve
prosthesis 26, the prosthesis 50 does not interfere with leaflet function.
Referring to FIGS. 9 and 10, still another presently preferred heart valve
prosthesis generally designated 70 is illustrated. The prosthesis 70
differs from the embodiments illustrated in FIGS. 2 and 4 primarily in
that the prosthesis has a more flexible construction. With particular
reference to FIG. 10, the prosthesis 70 is interiorly provided with a
flexible interior spine 78 preferably formed of braided dactron tape. The
flexible spine 78 is sutured at 79 to a second velour fabric 80.
Preferably, the fabric 80 is a double velour fabric for maximizing the
advantages of early endotheliazation.
The first fabric spine 78 is desirably folded axially and rolled into the
velour fabric 80. The velour fabric 80 is sufficiently greater in lateral
dimension that the entire spine fabric 78 is sheathed within the velour
fabric 80. The velour fabric 80 is then sutured as at 77 along the forward
edge of the prosthesis 70.
The flexible prosthesis 70 thus constructed, can be easily configurated in
any one of a variety of suitable heart valve configurations including both
of those illustrated in FIGS. 2 and 4. The broken line position
illustrated in FIG. 9 represents the configuration into which the
prosthesis would be configurated upon placement during mitral valve
annuloplasty. The length of the prosthesis 70 is specifically constructed
such that the ends 72 and 74, when displaced into the proper
configuration, will be spaced so as to correspond essentially to the
arcuate distance between commissures of the mitral heart valve leaflet.
Clearly, the length of the prosthesis 70 may be varied to correspond to
any selected heart valve subject to valvular annuloplasty. This flexible
prosthesis embodiment has been found highly effective in restoring valve
function by constricting the valve annulus without interfering with
leaflet mobility.
The invention may be embodied in other specific forms without departing
from its spirit or essential characteristics. The described embodiments
are to be considered in all respects only as illustrative and not
restrictive and the scope of the invention is, therefore, indicated by the
appended claims rather than by the foregoing description. All changes
which come within the meaning and range of equivalency of the claims are
to be embraced within their scope.
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