U.S. patent application number 09/982609 was filed with the patent office on 2002-02-28 for heart valve having tissue alignment with anchors and an outer sheath.
Invention is credited to Hemsley, David, Lane, Ernest, Tompkins, David.
Application Number | 20020026238 09/982609 |
Document ID | / |
Family ID | 22582838 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020026238 |
Kind Code |
A1 |
Lane, Ernest ; et
al. |
February 28, 2002 |
Heart valve having tissue alignment with anchors and an outer
sheath
Abstract
An apparatus and a method for constructing a heart valve
prepared from autologous tissue is disclosed. Three tissue leaflets
are held in place with tissue anchors on a tissue mounting frame
having an annular base and a plurality of commissure posts
extending from the base. An elastomeric sheath rests gently on the
tissue leaflets to prevent the leaflets from coming off of the
anchor hooks and encloses the leaflets to form valve cusps. The
leaflets touch each other on a coaptation line with an angle of
approximately 65.degree. C. relative to the commissure post. The
heart valves can be constructed intraoperatively in a short time,
typically ten minutes. The low coaptation angle and the fact that
the leaflets are held in place without being clamped between two
unyielding members minimize stress on the tissue.
Inventors: |
Lane, Ernest; (Huntington
Beach, CA) ; Tompkins, David; (Surrey, GB) ;
Hemsley, David; (Hertz, GB) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
620 NEWPORT CENTER DRIVE
SIXTEENTH FLOOR
NEWPORT BEACH
CA
92660
US
|
Family ID: |
22582838 |
Appl. No.: |
09/982609 |
Filed: |
October 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09982609 |
Oct 16, 2001 |
|
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|
09161809 |
Sep 28, 1998 |
|
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Current U.S.
Class: |
623/2.14 ;
623/2.41 |
Current CPC
Class: |
A61F 2/2415 20130101;
A61F 2220/0075 20130101; A61F 2/2409 20130101; A61F 2/2412
20130101 |
Class at
Publication: |
623/2.14 ;
623/2.41 |
International
Class: |
A61F 002/24 |
Claims
What is claimed is:
1. A heart valve comprising: a frame comprising an annular base and
a plurality of posts extending from said base; a plurality of
tissue anchors attached to said frame; a plurality of tissue
leaflets retained by said tissue anchors; and a flexible
elastomeric sheath, wherein said sheath fits around said frame and
said tissue leaflets and retains said tissue leaflets on said
tissue anchors.
2. The heart valve of claim 1, wherein said elastomeric sheath self
adjusts to apply substantially equal force to said tissue leaflets
on said frame.
3. The heart valve of claim 1, wherein the tissue leaflets are
supported and retained by the combination of (i) said tissue
anchors and (ii) said elastomeric sheath engaging a peripheral
portion of said tissue leaflets between said elastomeric sheath and
said frame, without clamping said tissue between two unyielding
members.
4. The heart valve of claim 1, comprising 3 tissue leaflets
retained by said tissue anchors.
5. The heart valve of claim 1, wherein said tissue leaflets
comprise partially fixed autologous tissue.
6. The heart valve of claim 1, wherein said tissue leaflets
comprise partially fixed autologous pericardial tissue.
7. The heart valve of claim 1, wherein said frame is covered with a
fabric.
8. The heart valve of claim 1, wherein said elastomeric sheath is
covered with a fabric.
9. The heart valve of claim 1, additionally comprising a flexible
annular sewing ring.
10. The heart valve of claim 9, wherein said elastomeric sheath and
said annular sewing ring are attached to said frame.
11. The heart valve of claim 1, wherein said tissue leaflets are
assembled to said frame intraoperatively during a valve replacement
operation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of Application Ser. No.
09/161,809, filed Sep. 28, 1998.
FIELD OF THE INVENTION
[0002] This invention relates to improvements in heart valves using
autologous tissue held in place by anchors and an outer sheath. The
heart valve can be constructed intraoperatively within a short
time, typically 10 minutes.
BACKGROUND OF THE INVENTION
[0003] Several types of heart valves are presently available for
use in replacing diseased or malfunctioning heart valves in
humans.
[0004] One form of heart valve is constructed from animal tissue,
typically from bovine or porcine aortic valve tissue. These valves
must typically be constructed in a laboratory well in advance of
when they will be needed and then stored in an aldehyde solution.
Skilled technicians are required to assemble these valves. The
valves constructed from animal tissue have relatively short
lifetimes. The short lifetimes are caused by two factors. First,
there is an antigenic reaction by the body to the animal tissue
which causes the tissue to calcify, making it inflexible and more
susceptible to failure with time. Second, the tissue is often
stored in glutaraldehyde before implantation to try to decrease the
antigenic reaction. The aldehyde tends to tan the tissue to a
leather-like consistency, which makes it wear out from the repeated
stress of opening and closing.
[0005] Thus, although these animal tissue valves are widely used,
they have to be replaced after about five to ten years. Replacing
the valves poses risks to the patient, because a second open heart
operation is then needed, with the attendant possibility of
problems during the operation.
[0006] Mechanical heart valves are also available. These valves are
made from hard, non-biological materials such as metals or
ceramics. Although the mechanical heart valves are durable, the
hard, non-biological surfaces on the valves tend to cause blood
clots. The blood clots can cause heart attacks or strokes, and, as
a result, patients with mechanical heart valves must take
anticoagulant drugs. These drugs can lead to hemorrhagic
complications. Also, patients on these drugs require frequent and
life-long laboratory tests of their clotting time.
[0007] Another type of heart valve, the autogenous tissue valve, is
constructed with the patient's own tissue. A number of patents for
autologous tissue heart valves and methods of making autologous
tissue heart valves have issued to Autogenics, assignee of this
application, including U.S. Pat. Nos. 5,161,955 and 5,326,371.
SUMMARY OF THE INVENTION
[0008] The preferred embodiments provide improved apparatus and
methods for constructing an autologous heart valve. A significant
factor is that both the configuration of the autologous tissue and
its means for attachment to the frame of the valve prevent
deleterious stress on the tissue.
[0009] Accurate placement of the autologous tissue is provided by
forming pericardium tissue taken from the patient into three
separate tissue leaflets, each generally semi-circular shape and
having a plurality of tissue anchor holes located along a tissue
cusp line. The location of these tissue anchor holes correspond to
tissue anchor hooks permanently attached to a tissue mounting
frame.
[0010] These three leaves of tissue are placed sequentially on the
tissue anchor hooks of the tissue mounting frame so as to be
located completely around the circumference of the tissue mounting
frame. An elastomeric sheath is stretched over the exterior of the
tissue mounting frame. This sheath prevents the tissue from coming
off the tissue anchor hooks and rests gently on the tissue around
the cusp line such that the tissue forms a naturally closed
valve.
[0011] A significant feature is that the manner in which the
autologous tissue is supported prevents deterioration stress on the
tissue. The tissue is thus not clamped between two unyielding
members, but rather supported and retained by the combination of
anchors mated in tissue anchor holes and the elastomeric sheath
engaging a peripheral portion of the tissue leaflets between the
elastomeric sheath member and the inner tissue mounting frame.
[0012] Another feature is that the tissue leaflets are formed to
include sufficient extra tissue area to provide a physiologically
representative coaptation line angle to thereby reduce the stretch
in the tissue held in place by the sheath and thus further reduce
the stress in the tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of a preferred embodiment of an
assembled autologous heart valve constructed in accordance with
preferred methods;
[0014] FIG. 2A is a front view during manufacture of the inner
frame portion of the tissue mounting frame;
[0015] FIG. 2B is a front view during manufacture of the outer
frame portion of the tissue mounting frame;
[0016] FIG. 3A is a perspective view of the outer frame after it
has been rolled into a cylindrical configuration;
[0017] FIG. 3B is a perspective view of the inner and outer frames
concentrically joined together;
[0018] FIG. 3C is a perspective of the completed tissue mounting
frame with tissue anchors before it is covered with cloth;
[0019] FIG. 3D is an enlarged perspective view showing one of the
commissure post anchors;
[0020] FIG. 4 is an enlarged view of the commissure tissue
anchors;
[0021] FIG. 5 is an enlarged view of the cusp tissue anchor ;
[0022] FIG. 6 is a cross-sectional view taken along line 6-6 of
FIG. 3C;
[0023] FIG. 7A is a front view of one of the autologous tissue
leaflets;
[0024] FIG. 7B is a front view of the autologous tissue leaflet of
FIG. 7A, showing the excess tissue for overlap of the tissue
leaflets on the commissure hooks;
[0025] FIG. 8 is the cross-sectional view of FIG. 6 with the
addition of two overlapping autologous tissue leaflets;
[0026] FIG. 9A is a perspective view of the elastomeric sheath;
[0027] FIG. 9B is a cross-sectional view taken along line 9B-9B of
FIG. 9A;
[0028] FIG. 10A is a perspective view of the elastomeric sheath
attached to the tissue mounting frame;
[0029] FIG. 10B is a front view of the elastomeric sheath shown in
FIG. 10A;
[0030] FIG. 10C is a sectional view taken along line 10C-10C of
FIG. 1;
[0031] FIG. 11A is a sectional view taken along line 11A-11A of
FIG. 1;
[0032] FIG. 11B is a cross-sectional view of line 11B-11B of FIG.
1;
[0033] FIG. 11C is a cross-sectional view of line 11C-11C of FIG.
1;
[0034] FIG. 12A is a perspective view of the annular sewing ring
before it is covered with cloth;
[0035] FIG. 12B is a cross-sectional view taken along line 12B-12B
of FIG. 12A; and
[0036] FIG. 13 illustrates the reduced coaption angle .theta. of
the preferred embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0037] FIG. 1 illustrates a preferred embodiment of the assembled
autologous tissue heart valve 9. This valve uses the patient's own
tissue and is constructed intraoperatively from several factory
manufactured components. Referring to FIGS. 3C and 7A, these
components include a tissue mounting frame 40 (FIG. 3C) having a
plurality of tissue anchor hooks 34 and 36. This tissue mounting
frame 40 mounts three individual autologous tissue leaflets 50, one
such leaflet being shown in FIG. 7A. The final assembled
configuration of the three leaflets is shown at 90 in FIG. 1. An
elastomeric outer sheath 42 covers the tissue mounting frame and
assists in holding the tissue in place on the frame without placing
undue stress on the tissue leaflets. An annular sewing ring 70 is
mounted at the base of the tissue mounting frame and elastomeric
sheath and used in the conventional manner to hold the assembled
valve 9 in place within the patient's heart. As described below,
this valve is designed to be intraoperatively assembled by the
surgeon during the open heart procedure. Typical assembly times are
of the order of 10 minutes.
Tissue Mounting Frame 40
[0038] The components of tissue mounting frame 40 are shown in
FIGS. 2A, 2B, 3A, 3B, 3C, 3D, 4 and 5. Shown in FIG. 2A is the
inner frame 10 preferably manufactured with a base 12 having three
commissure posts 14 extending from the base. In the constructed
valve shown in FIG. 1, these commissure posts 14 are located along
the axis of the valve in the direction of blood flow through the
valve. Preferably, the three commissure posts 14 are spaced
uniformly along the inner frame so that when the inner frame is
assembled, the three commissure posts are separated by 120 degrees.
The posts are preferably connected with scalloped walls 16 and the
ends 18 of the inner frame are preferably slanted at an angle
rather than being perpendicular to the base 12. A plurality of
inner frame holes 20 are located along the perimeter of the
scalloped walls 16 and commissure posts 14.
[0039] The inner frame 10 may be made of a variety of materials
suitable for in vivo use, including certain metals and plastics.
Metal is generally preferred over plastic as a material of
construction and ELGILOY is an especially preferred metal for
fabricating the inner frame 10. DELRIN is an especially preferred
plastic.
[0040] FIG. 2B shows the outer frame 24 portion of the tissue
mounting frame 40. The outer frame, just as the inner frame, is
constructed with a base 12a with a plurality of commissure posts
14a connected by a scalloped walls 16a. The ends 18a of the outer
frame are also preferably slanted. A plurality of outer frame holes
26 are located along a cusp line 30, shown as a dashed line in FIG.
2B. This cusp line 30 is located close to the perimeter of the
scalloped walls 16 and commissure posts 14a. The number of inner
outer frame holes depend on the size of the valve but are generally
in the range of 21 to 24. As described below, the outer frame holes
are formed to be juxtaposed with the corresponding inner frame
holes when the inner and outer frames are assembled together. The
outer frame can also be made of a variety of materials including
certain metal and plastic. ELGILOY is especially preferred.
[0041] The general location of a weld area 32 is shown on FIG. 2B
with cross hatching. This weld area generally defines the area on
the inner surface of the outer frame 24 which is later welded to
the outer surface of the inner frame 10 to permanently bind the two
frames together.
[0042] The inner frame 10 and outer frame 24 are rolled to form a
cylindrical configuration. The appearance of the two cylindrically
shaped members are quite similar so that only the outer frame 24 is
shown in FIG. 3A. The two members 10 and 24 are then placed
concentrically together and spot welded in the weld area 32 around
the base 12 to form the structure shown in FIG. 3B. The frame ends
18 and 18a are placed 120 degrees apart when the two frames are
welded together.
[0043] Commissure post anchors 34 (FIG. 4) and cusp line anchors 36
(FIG. 5) are fabricated from metal, preferably ELGILOY. These
anchors 34, 36 each include hook portions and a tang portion (34a
and 36a), the latter being used to permanently attach the anchors
to the tissue mounting frame 40. The hook portions are inserted
from within the cylinder of the joined inner and outer frames
through the inner frame holes 20 and outer frame holes 26 so that
the hook portion extends outside of the surface of the outer frame
(as shown in FIGS. 3C and 3B). The tang portion 36 is spot welded
to the inner surface of the outer frame 24 through the
corresponding larger inner frame hole 20 located in the inner frame
10. As best shown in FIG. 6, the tang portion 34a abuts the inner
surface of the outer frame 24 and resides within the corresponding
larger inner frame hole 20. As shown in FIGS. 4 and 5, and as will
become clear below, the commissure post anchors 34 are slightly
longer than the cusp line anchors 36, because they hold two layers
of tissue rather than one layer for the cusp line anchors.
[0044] FIG. 3D shows a more detailed view of the commissure post
anchors 34 which extend through the outer frame hole 26 in the
outer frame 24. The tang portion of the commissure post anchor 34
is spot welded to the inner wall of the outer frame 24 through the
larger inner frame hole 20 (not shown) of the inner frame 10.
[0045] As shown in FIGS. 3C, 3D and 6, the hook portions on the
commissure post anchors 34 point upwardly, while FIG. 3C shows that
the hook portions of the cusp line anchors 36 point away and
downwardly from the cusp line 30. Normally, but not necessarily,
there are two commissure post anchors 34 on each commissure post
14.
[0046] The tissue mounting frame 40 is manufactured in several
sizes to suit the particular needs of the patient after the surgeon
has removed the patient's valve during open heart surgery. Typical
sizes in current use include 19, 21, 23 and 25 mm valves. The
number of cusp line anchors vary, depending on the size of the
tissue mounting frame. Normally, there are 6 commissure post
anchors (2 per post) and 15-18 cusp line anchors per valve. The
number of cusp line anchors depends on the size of the valve.
[0047] FIG. 6 shows a cross-sectional view of one side of the
assembled tissue mounting frame 40 showing the inner frame 10,
outer frame 24, and commissure post anchors 34. The two commissure
post anchors 34 are welded to the inner wall of the outer frame 24
through the inner frame holes 20. Although not shown, the cusp line
anchors 34 are similarly welded to the lower part of the frame
40.
[0048] After the inner frame 10, outer frame 24, commissure post
anchors 34, and cusp line anchors 36 have been assembled and welded
together, the assembled tissue mounting frame 40 is covered on both
sides with DACRON cloth 38 (see FIG. 11B). DACRON is the
trademarked name registered to DuPont for polyethylene
terephthalate.
[0049] Since it is difficult to illustrate the cloth in the
drawings, certain of the cross-sectional views, FIGS. 10C, 11B,
11C, show DACRON cloth 38 as a broken line 38 over the mounting
frame 40 as well as the sheath 42 and sewing ring 70, described
below. The commissure post anchors 34 and cusp line anchors 36
extend through the DACRON. As noted above, the spot welded anchors
are flush with and only slightly protrude (typically 0.003 inches)
above the inner surface of the inner frame. As a result, when the
frame is covered with DACRON, the inside surface is smooth, except
for the knitted surface of the DACRON. Covering the frame with
DACRON isolates the non-biological material, such as the metal of
the frame, from the body. It also accomplishes the purpose of
promoting tissue ingrowth into the interstices of the fabric, to
further isolate the non-biological material from the body and
integrate the valve into the heart. This helps avoid the problem of
thromboembolism. Additionally, it provides a gentle interface
between the metal and plastic components of the valve and the
tissue and helps to nurture the tissue and promote its viability by
allowing free passage of blood to the tissue.
[0050] Although the DACRON cover for the frame can be prepared in a
variety of ways, one advantageous method was described in U.S. Pat.
No. 5,163,955, herein incorporated by reference. A three-fingered
DACRON sock or glove is described and shown in FIG. 4A of the
patent. The three-fingered sock is formed by heat seaming sections
of DACRON fabric together utilizing either hot wire, hot soldering
iron, or ultrasonic techniques. Alternatively, the entire glove can
be woven or knitted as one piece. The glove is then turned inside
out (to remove the seam from the bloodstream), pulled over the
tissue frame and secured with a heat seam at the base of the glove.
Similar fabrication methods can be used for the other DACRON
coverings described herein.
Autologous Tissue Leaflets
[0051] The autologous tissue leaflets 50 have a roughly
semicircular shape as shown in FIG. 7A. Details of these leaflets,
including the manner in which they are formed, is provided below.
These tissue leaflets 50 are formed with a plurality of tissue
anchoring holes 58 located along a tissue cusp line 62, shown as a
dashed line on FIG. 7A. A tissue leaflet chamfer 66 is preferably
cut in one corner to identify which leaflet is to be placed on top
and overlap a portion of the preceding leaflet. During the
intraoperative construction of the valve, these tissue holes 58 are
fitted over the commissure post anchors 34 and cusp line anchors 36
to properly position the tissue leaflets to the assembled tissue
frame. The attachment of the tissue leaflets 50 to the commissure
post anchors is shown in FIG. 8. As shown, overlapping tissue
leaflets 50a and 50b are attached to the tissue mounting frame 40
by having the tissue anchoring holes 58 inserted over the hook
portions commissure post anchors 34. As a result, two layers of
tissue leaflets 50 are attached to each of the commissure post
anchors 34. However, only one tissue leaflet is present in the
lower part of the frame where the leaflets do not overlap. The cusp
line anchors 36 (not shown in its FIG. 8) have a hook portion that
does not extend as far out from the frame 40.
Elastomeric Sheath
[0052] The elastomeric sheath 42 is shown in FIG. 9A. This
elastomeric sheath has a generally similar shape to that of the
tissue mounting frame 40, with an annular elastomeric sheath base
44 and three elastomeric sheath commissure posts 46 extending from
the base. The elastomeric sheath commissure posts 46 are connected
with elastomeric sheath scalloped walls 48. A plurality of
elastomeric sheath holes 64 correspond in position and number to
those of the commissure post anchors 34 and the cusp line anchors
36 on the frame 40. The elastomeric sheath 42 is preferably made
from silicone rubber covered on both sides with DACRON cloth.
[0053] Additional views of the elastomeric sheath 42 are shown in
FIGS. 9A, 10A, 10B, 10C, 11A and 11B. Please note that the FIGS.
10A, 10B and 11A are for illustrative purposes only since the
sheath is shown in these figures attached to the frame 40 without
the autologous leaflets 50. Such would not occur during
construction of the valve since these leaflets would be first
attached to the tissue mounting frame 40 by the tissue anchors 34,
36 and only afterwards is the sheath 42 moved into position. The
cross-section of the elastomeric sheath 42, shown best in FIG. 9B,
is somewhat like an inverted "J" with two rims adjacent to the
elastomeric sheath base 44. The elastomeric sheath 42 is designed
to be stretch-fit over the assembled frame structure having the
three leaflets 50 attached. When the elastomeric sheath 42 is
stretched over the assembled frame structure, the tissue anchors 34
and 36 locate loosely within the DACRON covered elastomeric sheath
holes 50, as best shown in FIG. 11B.
[0054] The top of the inverted "J" of the outer elastomeric sheath
fits over the top of the commissure posts 14 of the frame 40. The
tissue leaflets 50 attached to the commissure post anchors 34 and
the cusp line hooks 36 and are then held in place between the inner
wall of the elastomeric sheath 42 and the tissue mounting frame 40.
The elastomeric sheath holes 64 accommodate the hook section of the
commissure post anchors 34 and cusp line anchors 36 which protrude
beyond the tissue. FIG. 10A shows the commissure post anchors 34
fitted into the elastomeric sheath holes 64.
[0055] The elastomeric sheath 42 is fixed by its DACRON cover to
the base of the frame assembly by thermally welding, suturing, or
sewing it to the DACRON cover of the frame assembly. The
elastomeric sheath 42 is also held in position on the commissure
posts 14 of the frame by a elastomeric sheath pocket 84 situated at
the top of the inverted "J" of the outer sheath (FIG. 11B).
Sewing Ring
[0056] A DACRON covered sewing ring 70, shown in FIGS. 11A, 11B,
11C and 12A, 12B, is located at the base of the assembled valve.
The sewing ring advantageously has a wedge shaped cross-section and
is preferably made of silicon rubber, though other materials can be
used, provided that they are flexible, resilient, and durable. The
sewing ring is thin and flexible so that it can accurately conform
to the scalloped shape of the aortic root when the valve is
implanted into the patient.
[0057] The sewing ring, tissue mounting frame, and elastomeric
sheath are joined together by joining all six layers of DACRON
together in a thermal weld point 110, shown in FIGS. 11B and 11C.
The thermal weld 110 is formed with the sewing ring almost in line
with the tissue mounting frame. When the sewing ring is moved into
the position shown in FIG. 11B, the weld point is hidden between
the sewing ring and the outer sheath. This prevents
thromboembolisms from forming on the relatively smooth surface of
the weld.
[0058] The tissue mounting frame, tissue anchors, and elastomeric
sheath comprise a kit which can be preassembled in the factory and
shipped for use in an operating room. The kit can be fitted
together and the elastomeric sheath aligned with the tissue
mounting frame in the factory. Preferably, the tissue mounting
frame, and elastomeric sheath are covered with DACRON, and the
layers of DACRON are welded together with the thermal weld point
110 shown in FIGS. 11B and 11C, as previously described.
[0059] Optionally, the kit can additionally comprise a sewing ring
attached to the tissue mounting frame and elastomeric sheath.
Preferably, the sewing ring is also covered with DACRON and is
attached to the tissue mounting frame and elastomeric sheath by
welding the six DACRON layers together in a thermal weld point 110,
as previously described.
Preparation of the Autologous Tissue Leaflets 50
[0060] The general shape of each tissue leaflet 50 is shown in FIG.
7A. The shape has been designed to form a cusp shape and to
minimize tissue stress. The length of tissue along the tissue cusp
line 94 is slightly greater than the cusp line length 30 of the
tissue frame, as shown in FIG. 2B, so that the extra tissue can
form a cup shape, a process not dissimilar from that used to form
the bust in ladies dresses. Although there is more tissue than
required for the cusp length, it is not sufficient to cause folds
or wrinkles in the tissue.
[0061] The tissue leaflets are typically cut with a tissue cutting
die configured to both the size of the ultimate valve and also to
provide for additional tissue on one side of the leaflet. Examples
of cutting dies suitable for cutting predetermined shapes in
autologous tissue are shown and described in U.S. Pat. Nos.
5,163,955 and 5,425,741. In the preferred embodiment, disposable
tissue cutting dies will be supplied and used in a housing which
may be non-disposable.
[0062] For use in the preferred embodiments, the cutting die is
configured so that the tissue leaflets 50 are cut in a manner to
take account of the extra tissue required for the overlap on the
commissure posts 14 as shown in FIG. 11B. The radius along the
coaptation line of the leaflet whose tissue, at the commissure
post, is on top of the adjacent leaflet (leaflet 50a in FIG. 11B)
is lengthened by the extra amount needed to overlay the inner
leaflet. The tissue cutting die or other cutting device is
configured to provide for this extra tissue on one side of the
leaflet and also chamfer one comer of the cut leaflet to identify
which leaflet is placed on top of the preceding leaflet. The tissue
leaflet chamfer 66 is shown in FIG. 7A.
[0063] The greater length of the side of the tissue leaflet which
is on top is shown in FIG. 10C. The radius along the coaptation
line of the leaflet whose tissue is on top of the adjacent leaflet
(leaflet 50a in FIG. 11B) is lengthened by the extra amount needed
to overlay the inner leaflet. The extra tissue, as measured from
the centerline of the tissue leaflet, is shown as the crosshatched
area 98 in FIG. 7B.
[0064] In addition to the tissue cutting die, other techniques can
be employed to precisely cut the tissue leaflets, examples being
water jet or laser cutting apparatus.
[0065] A feature of the preferred embodiment of the invention is
that it does not require a horizontal coaptation line. As shown in
FIG. 13, such a horizontal coaptation line 104 significantly
increases the stress in the tissue at the commissure post 14. This
is analogous to the tension required to hold a washing line very
taut compared to a line which is allowed to have a degree of
curvature. In the heart valves constructed according to preferred
embodiments, the outer elastomeric sheath 42 holds the tissue
leaflets 50a and 50b around the commissure post 14 of the tissue
mounting frame 40. The tissue length along the coaptation line is
more than twice the radius of the valve. Taking account of tissue
stretch, this extra tissue results in a coaptation to commissure
post angle of approximately 65 degrees labelled as 102 in FIG. 13.
This reduced coaptation angle .theta. greatly reduces the stress in
the tissue leaflets at the commissure post 14.
[0066] The tissue for constructing the tissue leaflets 50 is
preferably autogenous tissue, such as pericardial tissue, but it
may also be fascia lata, rectus fascia, or vein tissue. These
tissue sources are all relatively flimsy and difficult to handle.
This is because, once harvested, the tissue will have a thickness
of about 10-12 mils. By comparison, bovine pericardium is about
15-20 mils thick. After the tissue is harvested, it is usually
partially fixed by immersion in 0.625% glutaraldehyde solution for
approximately 10 minutes. This both toughens the tissue and makes
it easier to handle.
[0067] Other tissue sources besides autogenous tissue are, of
course, possible, such as bovine pericardium or other xenograft
tissue or the like. Further, homograft tissue is possible. These
tissues could be pre-cut by the valve builder or manufacturer
outside the operating room and stored via conventional methods. If
other tissue sources are used, however, the dimensions of the
components would be adjusted to accommodate the tissue, which is
generally thicker than the preferred tissue sources.
Intraoperative Valve Construction
[0068] The cleaning, harvesting, and fixing processes for the
autologous tissue are known in the art and described, for example,
in U.S. Pat. No. 5,163,955.
[0069] Following fixing, the three separate leaflets 50 are cut, as
described above.
[0070] The three leaflets, the dimensions of which allow for
overlap with the cropped comer 66 (FIG. 7A) are placed on top of
the preceding leaflets. The leaflets are placed sequentially on the
tissue anchor hooks 34, 36 in the cloth covered tissue mounting
frame 40.
[0071] The elastomeric sheath 42 is then rolled-up over the frame
40 and the mounted tissue leaflets so that the concave pocket 84
situated at the top of each elastomeric sheath commissure post
section 46 of the sheath 42 is hooked over to a commissure post 14
of the tissue mounting frame 40. In the preferred embodiment, the
DACRON covered elastomeric sheath rests gently on the tissue
leaflets around the cusp line (see FIG. 11C) such that the tissue
leaflets form the naturally closed valve shown in FIG. 1. Sheath 42
prevents the tissue leaflets 50 from coming off the tissue anchor
hooks 34, 36, and the sheath substantially encloses and "hugs" the
upper portion of the commissure posts 14 and the tissue leaflets
attached thereto, as shown in FIG. 10C, so that the adjacent
leaflets touch each other in the coaptation line.
[0072] The completed valve is tested and then mounted to a holder
for implantation in accordance with the teachings of the prior art.
See, e.g., U.S. Pat. No. 5,163,955.
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