U.S. patent application number 09/785976 was filed with the patent office on 2001-09-13 for expandable annuloplasty ring.
Invention is credited to Carpentier, Alain, Carpentier, Alexandre.
Application Number | 20010021874 09/785976 |
Document ID | / |
Family ID | 27536976 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021874 |
Kind Code |
A1 |
Carpentier, Alexandre ; et
al. |
September 13, 2001 |
Expandable annuloplasty ring
Abstract
An expandable annuloplasty ring which may either expand
spontaneously, in situ, as the patient grows or be expanded by
surgical intervention by balloon dilatation. The distensible
annuloplasty ring of the invention may be usable in pediatric
patients whose growth, subsequent to surgical implantation of the
ring, will necessitate subsequent enlargement of the ring to
accommodate growth of the annulus. The ring may include a solid
core of non-elastic material which plastically retains its shape
upon natural expansion of the annulus, or after surgical expansion.
A discontinuity may be positioned along the anterior side of the
ring or around the posterior side.
Inventors: |
Carpentier, Alexandre;
(Paris, FR) ; Carpentier, Alain; (Paris,
FR) |
Correspondence
Address: |
Stout, Uxa, Buyan & Mullins
c/o Edwards Lifesciences LLC
Law Dept.
One Edwards Way
Irvine
CA
92614
US
|
Family ID: |
27536976 |
Appl. No.: |
09/785976 |
Filed: |
February 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09785976 |
Feb 16, 2001 |
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09124657 |
Jul 29, 1998 |
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6217610 |
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09124657 |
Jul 29, 1998 |
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08898176 |
Jul 22, 1997 |
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09124657 |
Jul 29, 1998 |
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09100451 |
Jun 19, 1998 |
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09100451 |
Jun 19, 1998 |
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08898908 |
Jul 22, 1997 |
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08757693 |
Dec 3, 1996 |
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08283059 |
Jul 29, 1994 |
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5593435 |
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Current U.S.
Class: |
623/2.37 |
Current CPC
Class: |
A61F 2/2448 20130101;
A61F 2250/0082 20130101; A61F 2250/0004 20130101 |
Class at
Publication: |
623/2.37 |
International
Class: |
A61F 002/24 |
Claims
What is claimed is:
1. An expandable annuloplasty ring for implantation in a heart
valve annulus, comprising: a ring segment defining a periphery of
the ring discontinuous at a single location, the ring segment being
formed of a non-elastic material which is capable of deformation
and shape retention thereafter from expansion forces; and a
radially expandable fabric covering surrounding the ring segment to
enable attachment to the annulus.
2. The annuloplasty ring of claim 1, wherein the non-elastic
material is a material which exhibits plastic deformation
properties and creeps over time.
3. The annuloplasty ring of claim 1, wherein the non-elastic
material is a polyacetal.
4. The annuloplasty ring of claim 1, wherein the single location is
positioned in a more stable area of lower growth of the heart valve
annulus.
5. The annuloplasty ring of claim 4, wherein the ring is generally
D-shaped with a straight side, and the single location is in the
straight side.
6. The annuloplasty ring of claim 5, wherein the single location is
in the middle of the straight side.
7. The annuloplasty ring of claim 5, wherein the single location is
offset from the middle of the straight side.
8. The annuloplasty ring of claim 1, wherein the single location is
formed by a break in the ring periphery, so that the ring is
open.
9. The annuloplasty ring of claim 1, wherein the single location is
formed by a section of the ring that is relatively weaker than the
remaining section.
10. The annuloplasty ring of claim 1, wherein the fabric covering
has a longitudinal seam.
11. The annuloplasty ring of claim 1, wherein there is no inner
stiffening portion in the ring segment such that the ring has
sufficient pliability to spontaneously expand on growth of the
annulus, and sufficient plasticity to retain the expanded shape and
provide adequate support for the developing annulus.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. Ser. No.
09/124,657, filed Jul. 28, 1998, which is a continuation-in-part of
U.S. Ser. No. 08/898,176, filed Jul. 22, 1997, and a
continuation-in-part of U.S. Ser. No. 09/100,451, filed Jun. 19,
1998, which in turn is a continuation of U.S. Ser. No. 08/898,908,
filed Jul. 22, 1997. Both U.S. Ser. No. 08/898,176 and U.S. Ser.
No. 08/898,908 are continuations-in-part of U.S. Ser. No.
08/757,693, filed Dec. 3, 1996, which is a continuation of U.S.
Pat. No. 5,593,435, filed Jul. 29, 1994. The disclosures of these
prior applications are hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to medical devices,
and more particularly to an annuloplasty ring useable for surgical
correction of certain disorders of the atrioventricular (i.e.,
mitral and tricuspid) valves of the human heart.
BACKGROUND OF THE INVENTION
[0003] In many patients who suffer from disfunction of the mitral
and/or tricuspid valves(s) of the heart, surgical repair of the
valve (i.e., "valvuloplasty") is a desirable alternative to valve
replacement. One specific group of patients who are typically
candidates for such surgery is children who suffer from congenital
valvular anomaly (CVA) or rheumatic valvular disease (RVD).
[0004] Remodeling of the valve annulus (i.e., "annuloplasty") is
central to many reconstructive valvuloplasty procedures. In 1968,
Dr. Alain Carpentier published studies which demonstrated that such
remodeling of the valve annulus might be accomplished by
implantation of a prosthetic ring (i.e. "annuloplasty ring") to
stabilize the annulus and to correct or prevent valvular
insufficiency that may result from defect disfunction of the valve
annulus. Annuloplasty rings are typically constructed of a
resilient core covered with a fabric sewing ring. Annuloplasty
procedures are performed not only to repair damaged or diseased
annuli, but also in conjunction with other procedures, such as
leaflet repair.
[0005] The prior art has included numerous annuloplasty rings, such
as those described in U.S. Pat. No. 4,042,979 (Angell), U.S. Pat.
No. 4,290,151 (Massana); U.S. Pat. No. 4,489,446 (Reed); U.S. Pat.
No. 4,602,911 (Ahmadi et al.); U.S. Pat. No. 5,061,277 (Carpentier
et al.); and U.S. Pat. No. 5,201,880 (Wright et al.), as well as
International Patent Publication WO 91/17721 and Foreign Patent
Publication SU 197710.
[0006] One problem associated with the annuloplasty rings of the
prior art is that when such annuloplasty rings are implanted into
children or adolescents (such as pediatric patients with CVA or
RVD) the subsequent growth of the patient may render the
annuloplasty ring too small for its intended function, thus
abnormally constricting the annulus. The mitral annulus, for
example, typically grows from about 16 mm across its longest
dimension, to about 34 mm in adults. Follow-up surgery would be
necessary to replace the originally implanted annuloplasty ring
with a larger ring suitable for the then-current size of the
patient. However, the tissue of the heart valve annulus grows into
the fabric suture ring by design so that the ring is soon embedded
in living tissue, making such replacement surgery problematic.
Therefore, reconstructive valvuloplasty surgery on younger patients
is often done using just sutures to bolster the annulus, or in
conjunction with pieces of woven polyester or other biocompatible
material. Such repairs may restore the normal geometry of the
annulus, but are unlikely to maintain that geometry without
additional structural support, and therefore are associated with
less reliable and durable results.
[0007] Although some of the annuloplasty rings of the prior art
have incorporated means for adjusting the size of the ring at the
time of implantation, the inventors are aware of no prior art
annuloplasty ring constructed and equipped for post-implantation
size adjustment, in situ, to accommodate changes in annular size
due to growth of the patient.
SUMMARY OF THE INVENTION
[0008] The present invention provides an expandable annuloplasty
ring for implantation in a heart valve annulus. Desirably, the ring
is adapted to expand upon natural growth of the patient's annulus,
or upon application of a dilatation force surgically applied. A
fabric covering is preferably radially expandable.
[0009] In accordance with the invention, the annuloplasty ring may
be formed of a non-elastic polymer or other distensible material,
such as polyacetyl, which will remain distended after the
application of natural growth forces or outward dilatory pressure
has been terminated. Desirably, the non-elastic ring includes a
discontinuity positioned in a more stable area of lower growth such
as in the straight side of a D-shaped ring that is positioned on
the anterior side of the mitral valve annulus.
[0010] In a preferred method of repairing a heart valve annulus, an
adjustable annuloplasty ring is implanted in the annulus. The size
of the implanted annuloplasty ring may be adjusted by inserting a
dilation apparatus into the valve in which the annuloplasty ring is
implanted and distending the annuloplasty ring to a larger annular
size. The step of adjusting may include advancing a catheter
transluminally through the vasculature to a point where the distal
end of the catheter is positioned adjacent the valve wherein the
annuloplasty ring is implanted, and subsequently advancing said
dilation apparatus through said catheter and into its desired
position within the valve for subsequent dilation of the
annuloplasty ring. Alternatively, the ring may be capable of
expanding upon growth of the annulus. Expansion of the implanted
self-expanding annuloplasty ring may still be assisted by inserting
a dilation apparatus into the valve in which the annuloplasty ring
is implanted and distending the annuloplasty ring to a larger
annular size.
[0011] In accordance with a further aspect of the present
invention, a distensible annuloplasty ring is provided which may
expand, in situ, spontaneously from the forces exerted by growth of
the heart, or by way of transvascularly and/or transseptally
positionable valve expansion apparatus. When dilatory or outward
pressure is exerted against the ring, as may be accomplished
spontaneously from the forces exerted by growth of the heart, or by
way of a radially expandable member (e.g., a balloon or expandable
wire cage) introduced within the annulus of the remodeled valve,
such pressure will expand the ring to a larger annular size.
[0012] Still further in accordance with the invention, there is
provided a method for performing remodeling annuloplasty of an
atrioventricular valve, with, if necessary, a subsequent
transluminal and/or transeptal procedure for enlargement of the
annuloplasty ring to accommodate growth of the patient.
[0013] Further objects and advantages of the invention will become
apparent to those skilled in the art, upon reading of the following
Detailed Description of the Preferred Embodiments and consideration
of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a plan view of a first embodiment of the
adjustable annuloplasty ring of the present invention;
[0015] FIG. 2 is a partial cut-away plan view of a second
embodiment of the adjustable ring of the present invention;
[0016] FIG. 3 is a reduced plan view of a third embodiment of the
adjustable annuloplasty ring of the present invention;
[0017] FIG. 3a is an enlarged cut away plan view of a portion of
the annuloplasty ring of FIG. 3;
[0018] FIG. 4 is a sectional illustration of a human heart having
an adjustable annuloplasty ring of the present invention implanted
at the mitral position, and showing the manner in which a dilation
apparatus (e.g., a balloon catheter or expandable cage) may be
advanced through a catheter, positioned transeptally, and utilized
to effect in situ enlargement of the adjustable annuloplasty ring
in accordance with the method of the present invention;
[0019] FIG. 5 is a plan view of a further embodiment of an
adjustable annuloplasty ring of the present invention showing an
outer suture covering partially removed to expose an inner ring
structure;
[0020] FIG. 6 is a perspective exploded view of the annuloplasty
ring of FIG. 5 with the outer suture covering removed;
[0021] FIG. 7 is an enlarged cross-sectional view of one end of a
ring segment forming a portion of the annuloplasty ring of FIG. 5
taken along line 7-7 of FIG. 6;
[0022] FIG. 8 is a perspective view of an end of a coupling tube
forming a portion of the annuloplasty ring of FIG. 5;
[0023] FIG. 9 is a perspective view of an end of an alternative
coupling tube for the annuloplasty ring of FIG. 5;
[0024] FIG. 10 is a perspective view of an end of a ring segment
within a coupling tube of an alternative adjustable annuloplasty
ring of the present invention;
[0025] FIG. 11 is a plan view of a portion of a fabric tube
conventionally used in covering annuloplasty rings;
[0026] FIG. 12 is a plan view of a portion of an enlarged tube of
fabric material having a similar weave as the smaller tube shown in
FIG. 11, and used for the annuloplasty rings of the present
invention;
[0027] FIG. 13 is a plan view of the annuloplasty ring of FIG. 5
showing a section of the enlarged fabric tube of FIG. 12
surrounding the inner ring structure just prior to a final step in
forming the ring;
[0028] FIG. 14 is a plan view of an adjustable annuloplasty ring
made of a single discontinuous, non-elastic segment and a suturable
covering;
[0029] FIG. 15a is a partial sectional view of a four-part
expandable annuloplasty ring of the present invention;
[0030] FIG. 15b is a partial sectional view of a further four-part
expandable annuloplasty ring of the present invention;
[0031] FIG. 16 is a partial sectional view of a still further
four-part expandable annuloplasty ring of the present
invention;
[0032] FIG. 17 is a schematic view of an alternative four-part
expandable annuloplasty ring superimposed over a misshapen mitral
valve annulus;
[0033] FIG. 18a is a plan view of the expandable annuloplasty ring
of FIG. 17 after implantation to restore the proper shape to the
mitral valve annulus;
[0034] FIG. 18b is a plan view of the annuloplasty ring of FIG. 18a
after a period of time after implantation, and subsequent growth of
the mitral valve annulus;
[0035] FIG. 18c is a plan view of the annuloplasty ring of FIG. 18a
after further elapsed time and growth of the mitral valve
annulus;
[0036] FIG. 19 is a plan view of an embodiment of a three-part
expandable annuloplasty ring of the present invention illustrating
certain force and moment conventions;
[0037] FIG. 20 is a schematic plan view of the three-part
expandable annuloplasty ring of FIG. 19 in various stages of
expansion upon growth of the annulus;
[0038] FIG. 21 is a partially cut away plan view of an expandable
annuloplasty ring of the present invention utilizing telescoped
segments;
[0039] FIG. 22 is a cross-sectional view of the expandable
annuloplasty ring of FIG. 21 implanted in tissue;
[0040] FIG. 23 is a plan view of a further embodiment of an
expandable annuloplasty ring having telescoped segments and no
fabric covering; and
[0041] FIG. 24 is a plan view of the expandable annuloplasty ring
of FIG. 23 simulating the expansion thereof after a period of time
after implantation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] The following detailed description and the accompanying
drawings are intended to describe and show certain presently
preferred embodiments of the invention only, and are not intended
to limit the spirit or scope of the invention in any way.
[0043] The present invention provides annuloplasty rings which
correct various valvular deficiencies stemming from a number of
conditions such as congenital valvular anomaly (CVA) or rheumatic
valvular disease (RVD), are expandable after implantation, and
provide support over extended periods. In addition, the rings are
used in conjunction with other procedures, such as leaflet repairs.
Some annuloplasty rings presently available can be adjusted during
the step of implantation to better fit the ring to the particular
annulus size, but the nominal ring size then remains constant for
its implanted life. The post-implantation expandability of the
present ring prolongs its implanted life and eliminates later
surgical removal and replacement operations in some instances. The
expandable annuloplasty rings of the present invention are
primarily intended for implantation in pediatric or younger
patients whose annuli are not fully developed. Depending on the
final adult annulus size, the present ring could provide a
permanent annulus support for the life of the patient. Because of
the expandable nature of the rings, a resection operation may not
be necessary. Larger patients may have to undergo a second
reconstructive valvuloplasty operation, however, to ensure optimum
ring performance.
[0044] The adjustability of the ring can be accomplished in two
primary ways: surgically or naturally. In a surgical adjustment
method, a balloon dilatation catheter or other such device is
positioned within the ring annulus and expanded. This dilates the
ring and increments its size. Though the surgical expansion is
beneficial for some patients, one primary advantage of the present
ring over the prior art is the capability of the ring to
self-expand upon natural growth of the valve annulus. This natural
expansion obviates further surgery to adjust the ring size and is
thus preferable over the surgical expansion method.
[0045] In one embodiment, upon balloon dilatation or as the patient
grows, the ring incrementally expands and "locks" into gradually
larger sizes. The particular construction of the ring allows
incremental expansion and prevents contraction. The present
invention also discloses a number of annuloplasty rings that expand
upon growth of the natural annulus without structure for
maintaining (or locking) the expanded shape. The rings are intended
to conform to the shape of the natural annulus, and maintain or
approximate that shape as the annulus grows.
[0046] Although the various embodiments of the expandable
annuloplasty ring of the present invention are designed to correct
deficiencies in the mitral valve annulus, those of skill in the art
will recognize that other shapes of rings for correcting other of
the heart's annuli (such as the tricuspid annulus) may be
constructed in accordance with the teachings of the present
invention.
[0047] Closed, Ratcheted, Segmented Annuloplasty Rings
[0048] With reference to the drawings, FIG. 1-3 show alternative
ways of constructing the adjustable ring member 10, 10a and 10b of
the invention. The ring members 10, 10a and 10b shown in FIG. 1-3
have a generally "D-shaped" configuration which corresponds to the
normal anatomical shape of the mitral valve annulus during closure.
In the annulus, a straight portion is formed by the attachment of
the anterior leaflet. It will be appreciated that if these ring
members 10, 10a and 10b were intended for use in remodeling of the
tricuspid valve, they would have the generally egg-shaped
configuration of the normal anatomical shape of the tricuspid valve
annulus, with a portion of the annulus being tough and a portion
being flexible.
[0049] The ring member 10 shown in FIG. 1 comprises first 12,
second 14 and third 16 tubular segments. Each segment 12, 14, 16 is
coupled to the two other segments to form a substantially unitary
ring structure. The first segment 12 is tubular in configuration,
having open ends A and B into which the corresponding ends of the
second and third segments 14, 16 are inserted. The second segment
14 has a blunt tipped or closed first end C and an open tubular
second end D. The third segment 16 has blunt tipped or closed first
and second ends E and F, respectively.
[0050] The segments include integrally formed coupling structure on
adjacent ends to link the segments in a chain and define the
periphery of the ring. The first end C of second segment 14 is
inserted into the open second end B of the first segment 12. A
series of raised lugs or teeth 18a protrude from one side of the
portion of the second segment 14 which inserts into the second end
B of the first segment 12. A corresponding series of apertures or
detents 20a is formed in the side walls of the first segment 12.
The individual teeth 18a snap into and frictionally engage the
individual detents 20a, as shown.
[0051] Similarly, the first end E of the third segment 16 is
inserted into the open second end D of the second segment 14. A
series of raised lugs or teeth 18b protrude from one side of the
portion of the third segment 16 which inserts into the first end A
of the first segment 12. A corresponding series of apertures or
detents 20c is formed in the side wall of the first segment 12. The
individual teeth 18c snap into and frictionally engage the
individual detents 20c, as shown.
[0052] The individual teeth 18 are configured and constructed such
that upon application of an enlarging force, the segments 12, 14,
16 will spread apart and the teeth 18 will be caused to move out of
the detents 20 within which they are positioned and will slidably
advance and snap into the next available detent in the series,
thereby effecting one incremental increase in the annular size of
the ring. Further application of an enlarging force will cause the
teeth 18 to move to the next available detents 20 in the series,
thereby effecting a second incremental increase in size, and so on.
After an incremental expansion, the teeth 18a, 18b, and 18c are
shaped to prevent contraction of the ring member 10. This is
necessary to provide structural support for the constantly flexing
annulus to avoid collapse thereof.
[0053] A suture ring 38, formed of material such as a woven
polyester mesh, is mounted about the periphery of the ring member
10, 10a and 10b to facilitate suturing-in-place of the ring member
10, 10a and 10b to surrounding anatomical tissue.
[0054] FIG. 2 shows an alternative ring 10a comprising first and
second semi-annular tubular segments 30, 32 which are joined
together in end to end fashion, as shown, to form the desired
annular configuration of the ring 10a. Rack bars 34, 36 insert into
the opposing ends of the first and second tubular segments 30, 32.
Teeth 18 protrude laterally from the portions of each rack bar 34,
36 which insert into the juxtaposed ends of the first and second
semi-annular tubular segments 30, 32 as shown. Corresponding
apertures or detents 20 are formed in the side walls of the tubular
members 30, 32. The individual teeth 18 snap into and frictionally
engage the individual detents 20, as shown.
[0055] It will be appreciated that the components which make up the
ring member 10 need not necessarily be of tubular configuration as
shown in the embodiments of FIGS. 1 and 2. Indeed, as shown in FIG.
3, the ring member 10b may comprise a plurality of non-tubular
arcuate leaves 40, 42, 44, 46 assembled in overlapping relation to
one another and contained within a distensible outer sheath 48, as
shown. In this particular embodiment, each leaf 40, 42, 44, 46
includes coupling structure formed thereon for cooperating with
complementary structure on another leaf to allow expansion of the
ring 1Ob but restrict contraction thereof In the illustrated
embodiment, this coupling structure includes ratchet teeth 18 and
detents 20.
[0056] As mentioned above, the application of an enlarging force to
the ring 10a causes the semi-annular tubular segments 30, 32 to
move apart and the individual teeth 18 to advance, and seat within,
the next available detents 20, thereby increasing the size of the
ring 10a by a predetermined incremental amount. The enlarging force
may derive from manually applied dilatory pressure, or from
terisile forces on the ring applied by growth of the patient's
annulus. The former method of manual application of a dilatory
pressure is now described in the context of a balloon catheter.
Those of skill in the art will recognize, however, that there are
other surgical methods for applying an enlarging force to the
annuloplasty ring of the present invention.
[0057] Surgical Annuloplasty Ring Expansion
[0058] FIG. 4 shows schematic illustration of the human heart
having an adjustable annuloplasty ring 10 of the present invention
implanted at the mitral position therein. The anatomical structures
and major blood vessels of the heart are labeled, on FIG. 4, in
accordance with the following legend:
1 PV Pulmonary Veins PA Pulmonary Artery SVC Superior Vena Cava IVC
Inferior Vena Cava AO Aorta RA Right Atrium RV Right Ventricle LA
Left Atrium LV Left Ventricle IS Interatrial Septum AV Aortic Valve
Position MV Mitral Valve Position TrV Tricuspid Valve PuV Pulmonic
Valve
[0059] As shown in FIG. 4, the size of the annuloplasty ring 10 may
be adjusted through introduction of a guide catheter 50, via
catheterization of the superior vena cava such that the distal end
of the catheter is passed through the interatrial septum IS, using
known septal penetration technique, and into the left atrium LA. A
balloon dilation catheter 52, such as a valvuloplasty catheter of
the type commercially available, is then advanced through the lumen
of the guide catheter 50, and positioned such that the balloon 60
of the balloon catheter 52 is within the annulus of the mitral
valve MV. Thereafter, the balloon 60 is inflated, as shown, to
cause the adjustable annuloplasty ring 10 to expand to a larger
annular configuration.
[0060] In embodiments, such as those described and shown here above
in FIG. 1-3, it will be appreciated that the balloon 60 may be
expanded to a specific diameter which will evoke a single
incremental increase (i.e., from one notch to the next) of the
mechanical expansion-controlling system of teeth and notches formed
in the annuloplasty ring 10.
[0061] Similarly, when the annuloplasty ring 10 is implanted at the
tricuspid valve TrV it will be desirable to advance the guide
catheter 50 through the superior vena cava SVA to a point where the
distal end of the guide catheter 50 is positioned within the right
atrium RA of the heart. The balloon dilation catheter 52 is then
advanced to a point where the distal portion of the balloon
catheter 52 extends through the tricuspid valve TrV. Thereafter, a
balloon 60 will be dilated so as to expand an annuloplasty ring of
the present invention (not shown) when implanted within the
tricuspid valve TrV.
[0062] Natural Annuloplasty Ring Expansion (Self-Expansion)
[0063] In a preferred method of adjustment of the annuloplasty ring
10, no surgical intervention is necessary. In one example, a ring
10 having a major dimension of 20 mm is implanted in a child. Over
the developing years, the patient's annulus may grow to a size of
24 mm or larger. As the annulus grows, the ring 10 accommodates
this growth by incrementally increasing in size. The number of
incremental size increases depends on the number individual teeth
18 and detents 20, but is desirably at least two and no more than
four. In one specific example, therefor, two teeth 18 and
associated detents 20 are provided at the junction of each ring
segment and the ring is incrementally expansible in two to four
stages from 20 mm to 24 mm.
[0064] Alternative Closed, Ratcheted, Segmented Annuloplasty
Rings
[0065] FIGS. 5 and 6 illustrate another embodiment of an adjustable
annuloplasty ring 100 comprising a pair of identical ring segments
102 and 104 joined by a first coupling tube 106 and a second
coupling tube 108. The annuloplasty ring 100 includes an outer
fabric covering 110 having a circumferential seam 112 (partially
shown in FIG. 5). The covering 110 ftunctions as a sewing ring for
the annuloplasty ring 100. As with the earlier described
embodiments, the annuloplasty ring 100 has a generally D-shape with
a length dimension D and a width dimension W. The shape of a mitral
annulus is sometimes given in terms of its aspect ratio, or the
width W over the length D. A preferred aspect ratio is about 3/4,
although certainly not all healthy anatomies conform to this
ratio.
[0066] Commissures C are shown at opposed ends of a straight
portion of the ring 100. The commissures C delimit the relatively
straight area of attachment of the anterior mitral leaflet. This
forms a tough fibrous edge on the inner septal wall as contrasted
with outer flexible muscular portions of the mitral valve annulus.
Generally, growth of the annulus occurs in the muscular portions,
while the fibrous edge experiences minimal growth. Natural or self-
expansion of the ring is therefore caused by outward growth
generally along the axis of the straight portion, and growth
radially outward around the curved portions. As will be clear from
the description below, the construction of the adjustable ring 100
takes this natural growth into account and expands concurrently
with minimal stress on attaching sutures.
[0067] With reference to FIG. 6, each of the ring segments 102 and
104 comprises a short straight portion 114 terminating in a free
end 116, and a longer curvilinear portion 118 terminating in a
short curvilinear portion 119 and free end 120. The ends 116 and
120 will be referred to hereafter as the straight end and curved
end, respectively. The first coupling tube 106 is straight and
includes opposed open mouths 122 within which are received the
straight ends 116 of the ring segments 102 and 104. In this regard,
the ring segments 102, 104 are mirror images of each other across
the width axis of the ring, with their free ends 116 and 120 facing
each other. The second coupling tube 108 is curvilinear, conforms
to the shape of the short curvilinear portions 119 of the ring
segments 102 and 104, and includes opposed open mouths 124 for
receiving the curved ends 120.
[0068] Each of the ring segments 102 and 104 comprises a generally
cylindrical composite rod having an exterior portion 125
surrounding an interior stiffener 126. Preferably, the exterior
portion 125 is made of ultra-high molecular weight resin polymer.
More preferably, the exterior portion 125 is made of a polyacetal,
polyethylene, or an acetal resin. The interior stiffener 126 is
preferably made of a metallic rod such as titanium or Elgiloy.RTM..
The first and second coupling tubes 106 and 108 are preferably made
of Elgiloy.RTM., titanium, or other biocompatible metal.
[0069] The curvature of the second coupling tube 108 and the
curvilinear portion 118 is shown with respect to a horizontal axis
in FIG. 5. For purposes of orientation, the horizontal axis is
parallel to the length dimension D. More particularly, a line
tangent to the curve at the point at which the ring segment 102
extends within the coupling tube 108 makes an angle .epsilon. with
the horizontal. This angle is important for maintaining a preferred
shape, or aspect ratio, for the annuloplasty ring 100 upon
expansion, as described below.
[0070] As with the embodiments of FIGS. 1-3, the annuloplasty ring
100 is adjustable in size. When the ring 100 is assembled for
implantation, the straight ends 116 and curved ends 120 extend
within respective tubes 106 and 108 as seen in FIG. 5. From this
position, the ring segments 102 and 104 may gradually retract from
within the tubes 106 and 108 by an external or host-generated
force. More particularly, the annuloplasty ring 100, as with the
annuloplasty ring described previously, may be expanded upon
application of a dilatory force from a balloon catheter, or may be
expanded upon growth of the patient's annulus. In the latter
situation, the annuloplasty ring 100 is self-expanding and a
further procedure to extend a balloon catheter within the ring is
unnecessary. As the patient's annulus grows from childhood, the
annulus grows and the ring 100 gradually expands therewith.
[0071] As the ring is dilated or otherwise expands, the preferred
D-shape is retained due to the angle .epsilon. shown in FIG. 5.
That is, the straight ends 116 begin retracting from the first
coupling tube 106 along a common axis, while the curved ends 120
retract from the second coupling tube generally along a common
curve. Thus, as the ring segments 102 and 104 pull apart and their
ends retract from the respective coupling tubes 106 and 108, both
the long dimension D and the width dimension W increase. The
preferred angle .epsilon. ensures that these dimensions increase
proportionally to maintain approximately the aspect ratio shown in
FIG. 5. For example, an expandable ring 100 having an aspect ratio
of 3/4 may have an initial length dimension D of 16 mm, with a
width W of about 12 mm. Upon expansion, the length D increases to
24 mm, while the width W increases to about 18 mm. The maximum
expansion of the ring 100, as well as other telescoped rings, may
be limited by the need for an initially overlapping structure.
Preferably, the telescoped rings will have the capacity for
expanding at least 4 mm in the length dimension.
[0072] The angle .epsilon. is a function of the length of the
second coupling tube 108 and the curvature thereof which conforms
to the curvature of the portion 119 of the ring segments 102 and
104. It should be noted that the portions 119 of the ring segments
102, 104 may not have a uniform curvature along their length, and
the overall proportional shape or aspect ratio of the ring 100 may
change slightly by an insignificant degree.
[0073] Structure for Regulation of Annuloplasty Ring Expansion
[0074] The structure for regulating the displacement of the ring
segments 102, 104 with respect to the coupling tubes 106 and 108
will be described with reference to FIGS. 7 and 8. FIG. 7 is a
cross sectional view of the straight end 116 of the ring segment
102, as taken along the sectional line shown in FIG. 6. The
interior stiffener 126 is shown embedded within the exterior
portion 125. It can be seen that the interior stiffener 126 is
positioned off center with respect to the longitudinal axis of the
ring segment 102 to accommodate the expansion regulating structure
described herein. More particularly, the expansion regulating
structure includes a series of grooves extending along the ring
segment 102 from the straight end 116. Beginning closest to the
straight end 116, a terminal groove 128, an intermediate groove
130, and an elongated groove 132 of identical depth are formed in
series. The elongated groove 132 has a length approximately twice
the length of the terminal groove 128 or intermediate groove 130. A
secondary tooth 134 divides the terminal groove 128 from the
intermediate groove 130. The secondary tooth 134 includes an angled
front face 138 on the side of the intermediate groove 130, and a
back face 136 extending generally perpendicularly to the axis of
the ring segment 102 on the side of the terminal groove 128. A
primary tooth 140 separates the intermediate groove 130 from the
elongated groove 132, and includes a front face 144 and a back face
142. A stop face 146 defines an end of the terminal groove 128
opposite the secondary tooth 134, and a stop face 148 defines an
end of the elongated groove 132 opposite the primary tooth 140. The
curved ends 120 of the ring segments 102, 104 desirably include an
arrangement of alternating teeth and grooves similar to the
straight end 116 for mating with the second coupling member
108.
[0075] The front face 144 forms a shallower angle with respect to
the longitudinal axis of the straight end 116 than does the front
face 138 of the secondary tooth 134. In a preferred environment the
front face 144 makes an angle a of about 30.degree. with respect to
the longitudinal axis, while the front face 138 of the secondary
tooth 134 makes an angle P of about 45 .degree.. It will also be
noted that the height of the primary tooth 140 with respect to the
adjacent grooves is slightly less than the height of the secondary
tooth 134 with respect to its adjacent grooves. Furthermore, the
secondary tooth 134 is thicker in the axial direction than the
primary tooth 140. The effects of the differing face angles,
heights, and thicknesses of the teeth 134 and 140 on the ring
expansion will be described in greater detail below. It should be
noted, however, that the relative sizes and shapes of the teeth 134
and 140 are given by way of example only, and numerous variations
will be readily apparent by one of skill in the art from the
functional discussion below.
[0076] FIG. 8 illustrates one end of the first coupling tube 106
terminating in the open mouth 118. The coupling tube 106 includes
structure for mating with the aforementioned teeth and grooves
formed on the ring segment 102. More specifically, a plurality of
apertures separated by bridges is formed on the end of the coupling
tube 106, the apertures receiving the teeth on the ring segment
102. An elongated aperture 150 is formed farthest from the open
mouth 118, a first detent 152 is formed slightly closer to the open
mouth, and a second detent 154 is closest to the open mouth 118.
The length of the elongated aperture 150 is approximately twice the
length of both the first and second detents 152 and 154,
respectively. A first bridge 156 separates the elongated aperture
150 from the first detent 152 and includes a contact edge 157
facing away from the open mouth 118. A second bridge 158 separates
the first detent 152 from the second detent 154 and includes a
contact edge 159, again facing away from the open mouth 118. A
third bridge 160 separates the second detent 154 from the open
mouth 118, and forms a part of the open mouth. It can readily be
seen that the main portion of the coupling tube 106 is tubular in
shape, with the bridges 156, 158 and 160 being somewhat flattened.
In a preferred manufacturing step, the bridges begin as tubular
walls and are flattened into the illustrated shape after forming
the aperture 150 and detents 152 and 154, and after insertion of
the ring segments 102, 104. The second coupling tube 108 includes a
similar arrangement of apertures and bridges for mating with the
curved ends 120 of the ring segments 102, 104. Of course, those of
skill in the art will see that the expansion regulating structure
between the first coupling tube 106 and ring segments 102, 104 and
the second coupling tube 108 and ring segments may differ depending
on performance requirements.
[0077] The interaction of the teeth and grooves of the ring
segments 102 and 104 and the apertures and bridges of the coupling
tube 106 will now be described, with the understanding that the
same applies equally to the interaction with the second coupling
tube 108. With reference to FIG. 6, the straight ends 116 of the
ring segments 102 and 104 are initially inserted within the, open
mouths 122 of the first coupling tube 106. In this step of
assembly, the flattened bridges 156, 158 and 160 have not yet been
formed so that the coupling tube 106 between the mouths 122 is
entirely tubular. Each straight end 116 extends far enough within
the coupling tube 106 so that the primary tooth 140 projects and is
visible from the elongated aperture 150, as seen in FIG. 5.
Subsequently, the first, second and third bridges 156, 158 and 160
are deformed into their flattened shape as shown in FIG. 8 using
metal forming tools and anvils well known in the art. The grooves
formed in the ends of the ring segments 102, 104 accommodate the
bridges.
[0078] Following this operation, the straight ends 116 of the ring
segments 102 and 104 are captured within the tube 106. That is, the
primary tooth 140 is sized to interfere with the contact edge 157
formed by the first bridge 156. Likewise, a similar operation
captures the curved ends 120 within the second coupling tube 108.
Therefore, the ring segments 102 and 104 are effectively captured
within the tubes 106 and 108 to form the D-shaped ring 100. It
should be noted that although the elongated aperture 150 is shown
large enough to expose both the primary tooth 140 and secondary
tooth 134, it need only be large enough to separate and define the
first bridge 156 so as to create an interference between the
contact edge and the primary tooth. The minimum size of the ring
100 is limited by either contact between the stop face 148 and the
mouth 122, or by contact between the straight ends 116 of the ring
segments 102 within the coupling tube 106.
[0079] Regulated Annuloplasty Ring Expansion
[0080] The annuloplasty ring 100 is then surgically implanted
within the annulus of the patient using well known techniques with
the sewing ring or covering 110 secured to the annulus with
sutures. After a number of months or years, a balloon catheter may
be introduced into the patient's venous system to enlarge the ring
100. In a preferred embodiment, however, the ring 100 self-expands
upon application of natural annulus growing forces. More
specifically, the growth of the annulus pulls the ring segments
102, 104 away from each other and out of the coupling tubes 106 and
108. As mentioned previously, growth of the annulus occurs in the
muscular tissue areas outside of the straight portion of the ring
100 defined between the commissures C. This area grows and applies
tensile forces on the ring segments 102, 104 to eventually cause
the primary teeth 140 to deform underneath and past the first
bridges 156 into the first detents 152. When the primary teeth 140
clear the bridges 156, the back faces 142 prevent movement in the
reverse direction and maintain the incremental size expansion. Over
time, growth of the annulus acts on the ring segments to further
expand the ring 100. The secondary teeth 134 deform underneath and
past the first bridges 156, while the primary teeth 140 likewise
are forced past the second bridges 158 into the second detents 154.
The back faces 136 and 142 prevent movement in the reverse
direction and maintain the incremental size expansion of the ring
100. Still further growth of the annulus eventually retracts the
ring segments 102, 104 far enough from the coupling tubes 106, 108
to move the stop faces 146 against the contact edges 157 which
limits the maximum expansion of the ring 100. In practice, though
the annulus grows relatively symmetrically around its periphery
(except for the fibrous septal wall), the ring 100 may be expanded
upon interaction of one or more of the tooth/detent combinations
before the others. Exact synchronism in this respect is not
critical, however, and further natural annulus growth is expected
to even out the peripheral ring expansion.
[0081] The initial free expansion of the ring segments is regulated
by the interference between the primary tooth 140 and the first
bridge 156. Ultimately, the force of growth of the annulus is great
enough to deform the plastic tooth 140 underneath and past the
first bridge 156. The initiation and ease of this deformation is
partly regulated by the angle .alpha. of the front face 144. That
is, the steeper the angle .alpha. the greater the resistance to
deformation of the tooth 140. With a preferred angle of 30 degrees,
for example, the amount of force needed to enlarge the ring 100 is
relatively small. Additionally, the radial height of the primary
tooth 140 in relation to the position of the bridge 156 affects the
timing of and resistance to initial ring expansion. The taller the
tooth 140, the more resistance to deformation, and thus the longer
the period before expansion forces can enlarge the ring by forcing
the tooth 140 under or completely past the bridge 156. Finally, the
thicker the tooth 140 is in an axial direction the more resistance
there will be to deformation. Design specifications for various
ring configurations, and knowledge of patient characteristics
enables the surgeon to select the proper expansible ring 100 in
different situations. For example, the ring 100 shown in FIGS. 5-8
includes a primary tooth 140 that is shorter, thinner and has a
shallower face angle than the secondary tooth 134. Thus, less
expansion force is required to initially enlarge the ring 100 by
deformation of the primary tooth 140 than is required to
subsequently deform the secondary tooth 134 for a second
incremental expansion. In addition, as mentioned above, the second
incremental expansion must overcome not only the secondary tooth
134 and first bridge 156 interaction, but the primary tooth 140
interacts with the second bridge 158 and affects the force needed
to expand the ring. A design in which the initial expansion is
relatively easy and subsequent expansions become gradually more
difficult is preferable for pediatric applications where the
child's annulus is initially fairly weak, but increases in size and
strength over the predicted implanted life of the ring 100. The
force required to enlarge the ring 100 increases from the first
increment to the second because of the differing teeth, while the
strength capacity of the patient increases concurrently, so that
the differences in periods between incremental expansions are
reduced. This control of the expansion characteristics of the ring
100 enables the surgeon to better match rings to different
patients.
[0082] Alternative Expansion Regulation Structure FIG. 9
illustrates an alternative embodiment of a coupling tube 106' in
which the first and second bridges 156' and 158' are severed at
approximately their midpoint. Each bridge 156' and 158' includes a
pair of walls extending from the tubular main body of the coupling
tube 106' and terminating in opposed free ends 170 and 172,
respectively. Thus, the first and second bridges 156' and 158' are
effectively cantilevered from the tubular body. This configuration
encourages more rapid expansion of the annuloplasty ring 100 upon
application of natural annulus or balloon dilatation forces. That
is, the primary tooth 140 deforms to some extent, but also forces
the free ends 170 of the bridges outward. The third bridge 160
remains solid to provide a stop described above. Other variations
of the coupling tubes 106 and 108 are contemplated to reduce,
increase, or otherwise regulate the ease of retraction of the ring
segments 102, 104 therefrom.
[0083] FIG. 10 illustrates a further alternative ring segment 180
and coupling tube 182. In this version, the coupling tube 182
includes an elongated aperture 183 for receiving one or more
generally rounded bumps or protrusions 184 formed on the ring
segment 180. The protrusions 184 interfere with the walls of the
aperture 183 to nominally position the ring segment 180 with
respect to the coupling tube 182. Again, as described above,
external balloon or internal body forces pull the ring segment 180
in the direction of the arrow 185 so that a first protrusion cams
underneath the walls of the elongated aperture 183 and into a
detent 186. A number of the protrusions 184 and detents 186 may be
provided for various levels of adjustability. Furthermore, and
consonant with the discussion of the earlier embodiments, the wall
angles of the protrusions 184, their width, height, and even the
material or surface lubricity, may be varied to regulate the ease
of relative ring segment 180 and coupling tube 182
displacement.
[0084] Expandable Fabric Covering
[0085] The sewing ring or covering 110 is designed to stretch with
the expanding ring segments 102 and 104. The degree of stretchiness
in sewing ring fabrics depends primarily on the weave and
orientation thereof. Many different types of weaves are available,
and custom designed or specified fabrics for use with the
annuloplasty ring 100 can be obtained from textile design houses.
Of course, such specifications may increase the expense of each
ring considerably, and thus the present invention contemplates the
modification of fabric used to cover conventional sewing rings to
save expense. Specifically, FIG. 11 illustrates a conventional
fabric tube 190 used for covering annuloplasty rings and other
medical devices to provide an anchoring surface for sutures. The
weave 192 of the tube 190 is typically such that flexibility in a
radial direction is somewhat greater than in a longitudinal
direction. Note that the weave 192 is illustrated schematically and
should not be construed as an accurate rendition of any one stitch
pattern.
[0086] FIG. 12 illustrates a fabric tube 194 having an identical
weave 196 as the fabric tube 190 shown in FIG. 11, but of a
significantly larger diameter. Again, the weave 196 is less
stretchy in the axial or X direction as it is in the radial or Y
direction (as indicated by the coordinate axis). A series of cut
lines are formed in the tube 194 to provide individual tube
segments 200, seen nearly completely surrounding the ring 100 in
FIG. 13. These tube segments 200 are positioned around the
annuloplasty ring 100 and sewn along the circumferential seam 112.
In this manner, the orientation of the weave 196 is reversed from
conventional sewing ring coverings. That is, the axis in which the
weave 196 has maximum stretch is now oriented in a circumferential
direction around the annuloplasty ring 100. This orientation
accommodates growth or expansion of the ring 100 as the patient
grows.
[0087] Discontinuous, Inelastic, Annuloplasty Rings
[0088] FIG. 14 illustrates a still further embodiment of an
adjustable annuloplasty ring 220 configured in accordance with the
present invention. The ring 220 comprises a solid ring segment 222
having a straight section 224 and a curvilinear section 226, with
the straight section forming free ends of the curvilinear section.
The commissures C as described above are shown generally delimiting
the straight section 224. The straight section 224 includes facing
ends 228 so that the ring 220 is discontinuous, or open. The
discontinuity may be positioned as shown in the middle of the side
of the ring 222 connected to the fibrous septal tissue, or may
alternatively be offset from this symmetric position. Preferably,
however, the discontinuity is within the generally straight portion
between the commissures C between which there is less growth. This
ensures that a continuous segment of the ring 220 surrounds the
muscular portions of the annulus. The discontinuity may be formed
by a break in the ring periphery, so that the ring is open, or it
may be formed by a relatively weak or stretchable section of the
ring.
[0089] A fabric covering 230 surrounds the ring segment 222 and may
have a longitudinal seam 232. The ring 220 is designed to grow in
size along with the patient's annulus, or may be surgically
enlarged such as with a balloon catheter described above with
reference to FIG. 4. The segment 222 is preferably made of a
material which creeps over time; that is, the material exhibits
plastic deformation properties and may be, for example, a
polyacetyl. In this embodiment, there is desirably no inner
stiffening portion, as with the earlier embodiments. The ring 222
has sufficient pliability to spontaneously expand on growth of the
annulus, and sufficient plasticity to retain the expanded shape and
provide adequate support for the developing annulus.
[0090] Discontinuous, Segmented, Expandable Annuloplasty Rings
[0091] A further form of expandable annuloplasty ring of the
present invention comprises segments which are flexibly joined
together at junctions, and which do not form a continuous periphery
(in other words, the ring is open). Some annuloplasty rings of the
prior art are rigid and in one piece with a break in the periphery
to conform to certain anatomical features (notably the midpoint
along the connection point of the anterior leaflet in the mitral
orifice, and at the anteroseptal commissure in the tricuspid
orifice). However the rigidity of these designs prohibits any
expansion upon natural growth of the annulus, or even if a balloon
dilatation procedure was used. The present invention provides
discontinuous rings which are segmented, so as to pivot with
respect to one another at the junction regions. The segments are
sufficiently long and coupled together in a manner such that the
ring adequately supports the annulus, and corrects any defects.
Because of the pivoting action, however, the ring expands with the
growing annulus.
[0092] One primary benefit of constructing the expandable rings
with a discontinuity is the wider capacity for expansion. That is,
there is no initial constraint of providing overlapping structure,
as in the telescoped versions of the ring. Therefore,
theoretically, the ring could open up as wide as possible. Of
course, a preferred aspect ratio of the ring should be maintained,
and thus the expansion is limited in this regard. In one example, a
segmented open ring 100 having an aspect ratio of 3/4 may have an
initial length dimension D of 20 mm, with a width W of about 15 mm.
Upon expansion, the length D increases to 32 mm, while the width W
increases to about 24 mm.
[0093] An exemplary embodiment of a four-part discontinuous,
segmented, expandable annuloplasty ring 320 is seen in FIG. 15a.
The ring 320 shown is intended for support of the mitral valve, and
as such has a somewhat D-shape with a relatively straight side 322
and a convex portion 324 around the remaining periphery. The native
mitral annulus is not a flat plane, and the anterior portion of the
mitral annulus, which is relatively straight in plan view, extends
out of a plane around which the posterior leaflet side extends. The
straight side 322 of the ring 320 is thus designed to match the
anterior portion of the mitral annulus, while the convex portion
324 conforms to the relatively planar posterior leaflet side.
[0094] The expandable annuloplasty ring 320 includes four main
parts; two end segments 326a and 326b make up the straight side
322, while two curvilinear segments 328a and 328b define the convex
portion 324. It should be noted that the end segments 326 are not
entirely straight, and include slight curvatures to transition
toward the curvilinear segments 328. A fabric covering 330 and a
tubular sheath 332 encompass all four of the segments, which are
not otherwise connected.
[0095] Each of the segments 326 and 328 desirably comprise solid
cylindrical lengths of relatively rigid material, such as titanium,
Elgiloy, a thermoplastic or other polymer, or other such
biocompatible material. Alternatively, the segments 326 and 328 may
be semi-rigid, and exhibit some elasticity or plasticity. The
opposite ends of each of the segments 326 and 328 are preferably
rounded to protect the other components of the ring from scoring or
other abrasive damage in either assembly or use. Of course, those
of skill in the art will recognize that other configurations of
segments are possible, such as differing cross-sections, end shapes
and the like.
[0096] In a preferred embodiment, the tubular sheath 332 extends
from a first end 334a to a second end 334b of the ring 320. The
sheath 332 may be made of silicone, or other similar expedient and
closely conforms to the exterior diameter of the cylindrical
segments 326 and 328. At the terminal ends 334a, 334b the sheath
332 extends generally axially beyond the ends of the cylindrical
segments 326 to define a small cavity that is then filled with a
biocompatible material 336, such as silicone. The fabric covering
330 extends around the ends of the tubular sheath 332 and filler
material 336 and is stitched to close the ring ends 334a, 334b and
provide a fabric covering around the entire exterior thereof.
[0097] The cylindrical segments 326 and 328 are spaced from one
another within the tubular sheath 332 by small voids, such a shown
at 338 of the bottom of FIG. 15a. Sutures 340 or other similar
expedient are used to tighten the fabric covering 330 and tubular
sheath 332 in the region of the voids 338. In this manner, the
cylindrical segments 326 and 328 may easily pivot with respect to
one another, but are generally secured from relative misalignment
or longitudinal movement within the ring 320. The voids 338 thus
define three pivot regions between the segments around the ring
320.
[0098] A break or discontinuity in the ring 320 is provided between
the ring ends 334a, 334b, or in the anterior side of the ring. The
discontinuity enables the ring 320 to expand and the segments to
pivot with respect to one another. The open ring 320 can expand a
substantial amount to accommodate growth of an annulus from a size
of about 16 mm to an adult size of about 32 mm. In an alternative
embodiment, the discontinuity in the ring is bridged by a member
capable of great elongation, such as a length of stretchable
material. In this manner, the ring is not "open" per se, but has a
discontinuity in that one section is relatively more expandable
than the remaining ring periphery.
[0099] In an alternative embodiment, an expandable annuloplasty
ring 342 seen in FIG. 15b is substantially identical to the ring
320 of FIG. 15a, with the exception that the voids 338 previously
disclosed are now filled with a pliable or otherwise soft material
344. The remaining elements of the ring 342 are given the same
numbers as in FIG. 15a. Again, the filler material 344 may be an
injectable silicone or other such biocompatible material. The
filler material 344 is preferably injected through the fabric 330
and sheath 332 into the voids 338 after the segments 328 are
positioned within the sheaths. The filler material 344 helps
maintain a preferred shape of the ring 342 prior to implantation,
and thus may be an aid for the surgeon. Of course, techniques of
implantation using a rigid template are available, and would firmly
maintain the ring shape regardless of the relative flexibility of
the coupling regions.
[0100] A still further embodiment of a four-part expandable
annuloplasty ring is seen at 346 in FIG. 16. Again, many of the
elements illustrated are similar if not identical with the elements
seen in FIG. 15a, and thus wherever appropriate like numbers will
be repeated. The ring 346 includes the relatively linear segments
326a, 326b, and the curvilinear segments 328a, 328b, as well as the
continuous surrounding fabric covering 338 and sheath 332. In
contrast to the first embodiments, there are no sutures pinching
the material in the regions between the cylindrical segments 326
and 328. Instead, regions 348 include filler material 350 between
the cylindrical segments. Because of the relative rigidity of the
segments 326 and 328 in contrast to the pliable filler material
350, the regions 348 serve as pivot points for the annuloplasty
ring 346.
[0101] FIG. 17 schematically illustrates a four-part expandable
annuloplasty ring 360 superimposed over a misshapen mitral annulus
361. Only the cylindrical segments of the annuloplasty ring 360 are
shown for simplicity. In this regard, the ring 360 includes two
straight segments 362a and 362b, as well as two curvilinear
segments 364a and 364b. The ring 360 is a slightly modified form of
the rings 320, 342 or 346 in that the straight segments 362 are
shorter than before and entirely straight. The pivot regions
between the segments 362 and 364 are schematically indicated by
small dashed connecting lines 365, and may be formed of the voids
or pliable filler material between the segments, or other structure
as will be appreciated. The mitral annulus 361 comprises a
posterior leaflet 366 attached around a convex posterior side 368,
and an anterior leaflet 370 attached along a straight (in plan
view) anterior side 372. As seen in FIG. 17, one potential
deformation of the mitral annulus is relative widening in the
anterior-posterior direction, accompanied by relative shortening in
the transverse direction. As a result of the misshapen annulus
there may be improper coaptation between the leaflets 364 and 368
and a gap 374 formed causing valvular insufficiency or
regurgitation.
[0102] To correct the valvular deficiency, the annuloplasty ring
360 is implanted around the annulus as seen in FIG. 18a. The arrows
in FIG. 17 indicate the directions that the periphery of the
annulus must move to implant the ring 360. Techniques for
implanting annuloplasty rings are well known in the art and will
not be described herein, other than to note that traditionally,
evenly spaced sutures are used to join the fabric covering and
adjacent tissue. After the annuloplasty ring 360 has been secured
around the mitral annulus, the gap 374 shown in FIG. 17 disappears
and the posterior leaflet 366 properly coapts with the anterior
leaflet 370. The cylindrical segments 362 and 364 have sufficient
rigidity to provide the proper physical support to the deficient
annulus, and maintain its natural physiological shape. Although the
pivot regions 365 permits some flexibility between the segments 362
and 364, the juxtaposed ends of adjacent segments are maintained in
axial aligmnent, thus maintaining the desired shape of the
annuloplasty ring 360. The annuloplasty ring 360 is initially sized
for the not yet fully developed annulus.
[0103] FIG. 18b illustrates the same annuloplasty ring 360 as seen
in FIGS. 17 and 18a, after growth of the mitral valve annulus 361.
As can be seen from the drawing, the overall shape of the
annuloplasty ring 360 remains substantially the same as when
initially implanted, but the size has increased. More specifically,
the left and right curvilinear segments 364a and 364b have spread
out from one another, as permitted by the lower pivot region 365,
and the discontinuity in the ring 360 provided in the anterior side
between the opposing ends of the short segments 362a and 362b. In
addition, the short segments 362 have pivoted slightly outward with
respect to the curvilinear segments 364, as permitted by the pivot
regions 365 therebetween. The end result is that the mitral valve
annulus 361 remains properly supported by the annuloplasty ring
360, with the leaflets 366 and 370 maintaining good coaptation with
no gap therebetween.
[0104] In a final view of the sequence of growth of the mitral
valve annulus 361, FIG. 18c illustrates the annuloplasty ring 360,
which has expanded from the size of FIG. 18b, maintaining proper
anterior/posterior geometry. Again, the curvilinear segments 364
have further spread apart about the lower pivot region 365, while
the short linear segments 362 are permitted to pivot with respect
to the curvilinear segments. The mitral valve annulus 361 is
properly supported so that the leaflets 366 and 370 meet with good
coaptation.
[0105] With reference now to FIG. 19, a three-part embodiment of a
discontinuous, segmented, expandable annuloplasty ring is shown.
The three-part annuloplasty ring 380 comprises a generally linear
segment 382 and two curvilinear segments 384a and 384b. The
generally linear segment 382 is pivotally coupled to the
curvilinear segments 384 at pivot regions 386. More specifically, a
first end 388 of each of the curvilinear segments 384 is pivotally
coupled to one of the ends of the generally linear segment 382. A
break or discontinuity in the ring 380 is formed between the second
ends 390 of each of the curvilinear segments, or around the
posterior side of the ring. The discontinuity allows the
curvilinear segments to spread apart with respect to one
another.
[0106] The annuloplasty ring 380 is shown superimposed over a
misshapen mitral valve annulus 392, seen in dashed line. As with
the four-part annuloplasty ring 360 of FIGS. 17 and 18, upon
implantation using a number of well known surgical techniques the
three-part annuloplasty ring 380 corrects the misshapen annulus
392. The generally linear segment 382 is implanted along a portion
of the annulus to which the anterior leaflet attaches. This portion
is generally considered to be more fibrous and less flexible than
the remaining periphery of the annulus. The curvilinear segments
384, on the other hand, are implanted around the posterior side of
the annulus that comprises flexible muscular tissue and is subject
to a larger growth rate than the anterior side. Therefore, over
time, the generally linear segment 382 is relatively stable, while
the curvilinear segment 384b spreads outward with the growing
annulus and pivots about its first end 388, as permitted by the
pivot region 386.
[0107] As will be understood by those of skill in the art,
correction of a mitral valve annulus such as a shown in the dashed
line 392 imposes certain forces on the curvilinear segment 384b.
FIG. 19 illustrates force and moment conventions imposed on the
curvilinear segment 384b after implantation and correction of the
mitral valve annulus. More particularly, the transverse dimension
of the annulus 392 perpendicular to the anterior-posterior
dimension is increased upon implantation of the ring 380.
Stretching the tissue outward in this manner tends to impose an
inward force on the curvilinear segments 384 as shown by the force
arrow F.sub.1. F.sub.1 is shown acting along an axis of greatest
transverse dimension of both the annulus 392 and a ring 380.
Conversely, the anterior-posterior dimensions of the annulus 392 is
reduced upon implantation of the ring 380, which tends to impose an
outward spring force on the ring along that axis. That force is
represented by the force arrow F.sub.2 acting outward at the second
end 390 of the curvilinear segment 384b. Of course, in reality the
forces imposed on the ring 388 by the corrected annulus 392 are
distributed more evenly than the summed forces shown, which are
used for purposes of clarity to illustrate the preferred design of
the annuloplasty ring 380.
[0108] Assuming the curvilinear segment 384b pivots about the first
end 388, the force F.sub.1 acts along a moment arm having a length
r.sub.1, thus setting up moment M.sub.1. At the same time, the
force F.sub.2 acts along a moment arm having a length r.sub.2, thus
setting up a counter-balanced moment M.sub.2. The two moments
M.sub.1 and M.sub.2 cancel each other now so that the annuloplasty
ring 380 retains its initial pre-implantation shape. In other
words, the ring 380 is designed so that the moments imposed on it
after implantation and beyond are in equilibrium, to ensure the
initial ring shape is maintained. Furthermore, the material of the
curvilinear segments 384 are of sufficient rigidity to prevent
bending.
[0109] It should be noted that the precise forces imposed on the
annuloplasty ring 380 after implantation in any particular patient
cannot be determined with great accuracy prior to surgery, and then
only with careful measurements, which may be impractical. To
estimate the forces that may be imposed on the ring 380, a body of
empirical data regarding misshapen mitral valve annuli in
combination with careful geometric design considerations would be
useful. Such data regarding the forces imposed by mitral valve
annuli may be obtained from studying animal subjects with similar
anatomical features, such as pigs, or by studying human subjects
during autopsy. Ultimately, the data should enable those skilled in
the art to predict the forces associated with correcting a
misshapen annulus, and design the annuloplasty ring accordingly.
Such research may spur the design of a number of different
expandable ring configurations with gradually varying pivot
locations, for example, to enable the surgeon to find a best match
for the particular valvular deficiency. Indeed, the discussion with
respect to forces and moments imposed on a three-part annuloplasty
ring, such as shown in FIG. 19, applies equally to the four-part
rings as shown earlier, and other configurations of expandable
annuloplasty rings.
[0110] Expansion of the annuloplasty ring 380 of FIG. 19 is seen in
schematic in FIG. 20. As mentioned previously, the generally linear
segments 382 remains relatively stable, while the curvilinear
segments 384 pivot therefrom and spread apart. The break or
discontinuity between the second ends 390 of the curvilinear
segments 384 becomes larger as the patient's annulus grows. The
dashed lines 400 for the two larger sizes represent imaginary
extensions of the curvilinear segments 384 toward one another. It
can thus be seen that the overall shape of the annuloplasty ring
380 is substantially maintained even in its expanded
configurations.
[0111] Continuous, Segmented, Expandable Annuloplasty Rings
[0112] In another form of the present invention, the annuloplasty
ring comprises segments which are coupled together in a telescoped
manner. Unlike the earlier described telescoped embodiments which
included various structure to prevent the segments from contracting
after expansion, this embodiment allows both expansion and
contraction. Because of the foreign body response of the patient, a
tubular sheath of tissue forms around annuloplasty rings. By
allowing the segments to freely slide circumferentially, the
telescoped, segmented ring can expand with the growing tissue
sheath.
[0113] FIGS. 21 and 22 illustrate a further embodiment of a
segmented, expandable annuloplasty ring 410 which maintains a
continuous periphery throughout growth of the annulus, and relies
on telescoping as opposed to pivoting segments. FIG. 21 illustrates
the ring 410 in plan view with a portion of an outer fabric
covering 412 cut away to expose the working elements therein. The
ring 410 comprises a pair of symmetrical and generally curvilinear
segments 414 joined by a pair of tubular sheaths 416 and 417. The
segments 414 each comprise a generally linear portion 418 which
corresponds to the region of the mitral annulus to which the
anterior leaflet attaches, and a curvilinear portion 420 which
corresponds to the region of the mitral valve annulus about which
the posterior leaflet attaches. The linear portions 418 of the
segments 414 meet at a junction 422, while the curvilinear portions
420 meet at a junction 424. Because of the generally D-shape of the
ring 410, the junctions 422 and 424 desirably lie along an axis of
symmetry of the ring; the segments 414 thus being mirror images of
one another.
[0114] In the initial, unimplanted, state of the ring 410, the
segments 414 are juxtaposed at the junctions 422 and 444. The
sheath 416, which is preferably linear, surrounds the linear
portions 418 of both segments 414 and the junction 422. Likewise,
the sheath 417, which is curvilinear, surrounds the junction 424
and a length of each of the curvilinear portions 420.
[0115] The arrangement of the elements of the ring 410 after
implantation is seen in cross-section in FIG. 22. After a
sufficient time has elapsed, the host organism foreign body
response creates a tubular growth of tissue 430 in and around the
fabric covering 412, thus encapsulating the elements of the ring
410 within. In a preferred embodiment, the segments 414 and sheaths
416 and 417 are made of a smooth material resistant to tissue
ingrowth. For example, the segments 414 may be made of a relatively
rigid material or a combination of biocompatible metal and
silicone, while the sheaths 416 and 417 are made of pliable
silicone or a biocompatible polymer. In this manner, the tubular
surrounding tissue 430 will not interfere with subsequent expansion
of the ring 410. That is, the ring elements relatively easily slide
with respect to and within the surrounding tissue 430. During
growth of the annulus, which naturally includes growth of the
surrounding tissue 430, the telescoped sections of the ring 410 are
able to move apart under influence of the growth forces of the
annulus. That is, the segments 414 will move apart which respect to
one another within the sheaths 416 and 417. The fabric covering 412
is highly elastic and expands with the growth of the surrounding
tissue 430.
[0116] A further embodiment of the telescoped configuration of
expandable annuloplasty ring the shown at 440 in FIG. 23. In this
version, three segments 442 initially have juxtaposed ends at
junctions 444. Sheaths 446 surround the junctions 444 as well as a
predetermined length of the respective segments 442. In this
embodiment, there is no fabric covering as in FIG. 21, and the
annuloplasty ring 440 is implanted by using a technique in which
sutures passed through the annulus are looped around the ring, as
opposed to being threaded through an associated fabric
covering.
[0117] FIG. 24 illustrates the shape of the ring 440 after a period
of growth of the host annulus. The segments 442 have been pull
apart so that their ends 448 are spaced with respect to one another
within the sheaths 446. The sheaths 446 are sufficiently long
enough to accommodate substantial growth of the ring 440 without
separation of the elements. Again, the shape of the segments 442
and sheaths 446 are such that upon growth of the annulus, the ring
440 maintains its approximate initial shape. The sheaths 446
between curvilinear portions of the segments 442 are deformed to
some extent because of the shape and rigidity of the segments, and
their separation. Nevertheless, the initial shape (i.e., aspect
ratio) is approximately maintained, and the annulus adequately
supported despite the slightly changing shape.
[0118] It will be appreciated by those skilled in the art that
various modification additions and deletions may be made to the
above-described embodiments, without departing from the intended
spirit and scope of the invention. Accordingly, it is intended that
all such modifications, additions and deletions be included within
the scope of the following claims.
* * * * *