U.S. patent application number 09/746379 was filed with the patent office on 2002-06-27 for polymer heart valve with helical coaption surface.
Invention is credited to Moe, Riyad.
Application Number | 20020082687 09/746379 |
Document ID | / |
Family ID | 25000584 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020082687 |
Kind Code |
A1 |
Moe, Riyad |
June 27, 2002 |
POLYMER HEART VALVE WITH HELICAL COAPTION SURFACE
Abstract
A polymer heart valve has a leaflet with a base geometry of a
cylinder for simplicity and effective opening. A helical swept
surface is added to the top of the cylinder to enhance stable
coaption. The heart valve includes a plurality of flexible
leaflets. Each leaflet includes a top portion and a bottom portion.
The bottom portion is an axial section of a cylinder having an axis
and a radius. A first section of the top portion is a surface
defined by a first arc having a first radius swept along a first
helix. The first arc is tangent to the axial section of the
cylinder. A second section of the top portion is a surface defined
by a second arc having a second radius swept along a second helix.
The second arc is tangent to the axial section of the cylinder. The
second helix is a left-handed helix having the same radius and axis
as the cylinder.
Inventors: |
Moe, Riyad; (Austin,
TX) |
Correspondence
Address: |
Timothy L. Scott, Senior Patent Counsel
SULZER MEDICA USA INC.
Suite 1600
3 East Greenway Plaza
Houston
TX
77046
US
|
Family ID: |
25000584 |
Appl. No.: |
09/746379 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
623/2.12 |
Current CPC
Class: |
A61F 2/2412
20130101 |
Class at
Publication: |
623/2.12 |
International
Class: |
A61F 002/24 |
Claims
What is claimed is:
1. A heart valve comprising: a body; a plurality of flexible
leaflets attached to the body, each leaflet including a top portion
and a bottom portion; the bottom portion being a surface defined as
a cylinder having an axis, a radius and an axial section; a first
section of the top portion being a surface defined by a first arc
having a first radius swept along a first helix, the first helix
being a right handed helix having the same radius and axis as the
cylinder; and a second section of the top portion being a surface
defined by a second arc having a second radius swept along a second
helix, the second helix being a left handed helix having the same
radius and axis as the cylinder.
2. The valve as defined in claim 1 wherein the first helix has a
first pitch and the second helix has a second pitch equal to the
first pitch.
3. The valve as defined in claim 1 wherein the first radius is
equal to the second radius.
4. The valve as defined in claim 1 wherein the surface of the
bottom portion has a curvature in one direction and the surface of
each of the first and second top portions has a curvature in
multiple directions.
5. The valve as defined in claim 1 including three identical
leaflets.
6. A heart valve comprising: a body; a plurality of flexible
leaflets attached to the body, each leaflet including a top portion
and a bottom portion; the bottom portion being a surface defined as
a cylinder having an axis, a radius and an axial section; a first
section of the top portion being a surface defined by a first arc
having a first radius swept along a first helix, the first arc
being tangent to the axial section of the cylinder, the first helix
being a right handed helix having the same radius and axis as the
cylinder; and a second section of the top portion being a surface
defined by a second arc having a second radius swept along a second
helix, the second arc being tangent to the axial section of the
cylinder, the second helix being a left handed helix having the
same radius and axis as the cylinder.
7. The valve as defined in claim 6 wherein the first helix has a
first pitch and the second helix has a second pitch equal to the
first pitch.
8. The valve as defined in claim 6 wherein the first radius is
equal to the second radius.
9. The valve as defined in claim 6 wherein the surface of the
bottom portion has a curvature in one direction and the surface of
each of the first and second top portions has a curvature in
multiple directions.
10. The valve as defined in claim 6 including three identical
leaflets.
11. The valve as defined in claim 6 wherein the leaflets are formed
of a synthetic material.
12. A method of forming a heart valve comprising: providing a body;
attaching a plurality of leaflets to the body; providing a top
portion and a bottom portion for each leaflet; forming the bottom
portion from a cylinder having an axis, a radius and an axial
section; forming a first section of the top portion by a first arc
having a first radius swept along a first helix, wherein the first
helix is a right handed helix having the same radius and axis as
the cylinder; and forming a second section of the top surface by an
arc having a second radius swept along the second helix, the second
helix being a left handed helix having the same radius and axis as
the cylinder.
13. The method as defined in claim 12 wherein the first helix has a
first pitch and the second helix has a second pitch equal to the
first pitch.
14. The method as defined in claim 12 wherein the first radius is
equal to the second radius.
15. The method as defined in claim 12 wherein the plurality of
leaflets includes three leaflets.
16. A method of forming a heart valve comprising: providing a body;
attaching a plurality of leaflets to the body; providing a top
portion and a bottom portion for each leaflet; forming the bottom
portion from a cylinder having an axis, a radius and an axial
section; forming a first section of the top portion by a first arc
having a first radius swept along a first helix, the first arc
being tangent to the axial section of the cylinder, wherein the
first helix is a right handed helix having the same radius and axis
as the cylinder; and forming a second section of the top surface by
an arc having a second radius swept along the second helix, the
second arc being tangent to the axial section of the cylinder, the
second helix being a left handed helix having the same radius and
axis as the cylinder.
17. The method as defined in claim 16 wherein the first helix has a
first pitch and the second helix has a second pitch equal to the
first pitch.
18. The method as defined in claim 16 wherein the first radius is
equal to the second radius.
19. The method as defined in claim 16 wherein the plurality of
leaflets includes three leaflets.
20. The method as defined in claim 16 wherein the leaflets are
formed of a synthetic material.
Description
TECHNICAL FIELD
[0001] The disclosures herein relate generally to prosthetic heart
valves and more particularly to tri-leaflet prosthetic heart valves
having polymeric valve leaflets.
BACKGROUND
[0002] Prosthetic heart valves for human patients have been
available since the 1950s, following the advent of blood
oxygenators, which made open heart surgery possible. Today, there
are three general types of prosthetic heart valves, including
mechanical valves, tissue valves and polymer valves. A heart valve
prosthesis is implanted into an annular opening in a patient's
heart following surgical removal of a diseased or damaged natural
valve. The valve can be secured in the annulus of the opening
through the use of sutures or pins that penetrate the host tissue
and an outside edge of the valve. Alternatively, the valve can be
secured in the annulus by suturing the host tissue to a sewing
ring. Heart valves function essentially as one-way check valves for
blood flow through the beating heart.
[0003] The term "mechanical valve" as used herein refers to
bi-leaflet heart valves comprising a valve orifice fabricated at
least in part of a rigid, biologically compatible material such as
pyrolytic carbon, and comprising essentially no biological
components. The term "bioprosthetic valve" refers to a bi-leaflet
or tri-leaflet heart valve comprising at least some biological
components such as tissue or tissue components. The biological
components of tissue valves are obtained from a donor animal
(typically bovine or porcine), and the valve may comprise either
biological materials alone or biological materials with man-made
supports or stents. The term "polymeric valve" refers to a
tri-leaflet or bi-leaflet heart valve comprising at least some
elastomeric polymer components, including at least elastomeric
polymer valve leaflets.
[0004] A bi-leaflet mechanical valve typically comprises an annular
valve body in which two opposed leaflet occluders are pivotally
mounted. The occluders are typically rigid, although some designs
incorporate semi-rigid leaflets, and the occluders move between a
closed position, in which the two leaflets are mated and block
blood flow in the reverse direction, and an open position, in which
the occluders are pivoted away from each other and do not block
blood flow in the forward direction. The energy of blood flow
causes the occluders to move between their open and closed
positions.
[0005] Flexible heart valves seal against reverse flow by having
leaflets whose total surface area is greater than the area of the
orifice. Sections of the leaflets, therefore, contact one another,
or coapt, to close the valve and prevent blood backflow. Coaptive
sealing occurs over an area on the leaflets, rather than merely
along their edges. Two leaflets are unlikely to seal with any
stability if they only contact line to line. This can cause
T-boning, or prolapse. T-boning occurs when the end of one leaflet
slips below the end of the mating leaflet during closing, forming a
line-on-line contact rather than an area contact.
[0006] Although both tissue and polymer valves involve flexible
leaflets, the degree of control possible for the shape of tissue
valve leaflets is extremely small, since the leaflets are formed
from tissue sheets that are trimmed and sewn to a valve stent.
Polymer valves, on the other hand, may be fabricated by molding,
casting, and other known techniques, and therefore allow much
greater control of valve body and leaflet shape. By precise control
of the leaflet shape, polymer heart valves may be fabricated with
improved wear and performance characteristics. In particular, by
providing leaflets having an analytic shape in a selected position
which can be represented generally by analytic geometry. An
analytic shape may include a portion of a cylindrical surface, of
an ellipsoid, of a paraboloid, or of another shape that can be
defined mathematically.
[0007] A tri-leaflet heart valve prosthesis typically comprises an
annular valve body and three flexible leaflets attached thereto.
The valve body comprises an annular base and three leaflet support
posts. A sewing ring annularly coupled to the periphery of the
valve body provides a place for sutures to be applied when the
valve is implanted. The leaflets are attached to the three shaped
posts along an attachment curve, and they also each have a free,
unattached edge remote from the attachment curve. The place where
two adjacent leaflets come together at one of the support posts is
called the commissure, and the generally curved area on the leaflet
between the free edge and the attachment curve is known as the
belly of the leaflet. The free edges of the three leaflets come
together at a "triple point" generally on the axis of the
valve.
[0008] One aspect of the sealing problem for tri-leaflet polymer
valves arises from the nature of the valve geometry. As already
noted, it is desirable to provide leaflets defined by an analytical
shape. Tradeoffs must be made, however, among various possible
geometries. In particular, it is desirable to provide a coaption
surface that seals efficiently and robustly. Many prior art
approaches to the difficult problem of leaflet design have been
made.
[0009] U.S. Pat. No. 4,888,009 shows a prosthetic heart valve
comprising leaflets of a spherical section, with no additional
coaption surface. While this design is simple to fabricate,
provides relatively good fabrication control, and has a small gap
between leaflets, the vertical component of the angle between the
surface tangents of opposed leaflets is not constant. For example,
at the triple point and commissures, the leaflet surface tangent is
nearly vertical, so the angle between the surface tangents of
opposed leaflets is small and an effective and robust seal is
facilitated in these regions. However, at the midpoint of the
leaflet free edge between the commissures and the triple point, the
leaflet surface tangent is much further from vertical.
Consequently, the angle between the surface tangents of opposed
leaflets is large, and the seal may not be effective or robust.
Small deviations in position or load might disrupt the sealing of
the leaflets and cause one free margin to slide below the other.
The leaflets would have a line of contact instead of an area of
contact.
[0010] Coaptive surfaces at the ends of the leaflet can be used to
prescribe the angle between the surface tangents at the ends of
opposing leaflets. The simplest shape for a coaptive surface is to
have a vertical surface (i.e., a surface oriented generally
parallel to the direction of blood flow) at the end of each
leaflet. Such surfaces appear to be vertically aligned when the
valve is in the closed position. For a tri-leaflet valve with
identical leaflets, two vertical coaption surfaces are actually
needed on each leaflet because each leaflet covers 120 degrees (not
180), and the leaflets must bend inward from the commissure to the
triple point before again bending back to the other commissure (see
FIG. 3). Tri-leaflet valves having vertical coaption surfaces,
therefore, all have three general surface areas: the belly of the
leaflet and the two coaptive surfaces. Many leaflet belly surface
configurations have been proposed (with and without vertical
coaption surfaces). Tri-leaflet valves having vertical coaption
surfaces all suffer from a particular problem. Although the sealing
of two vertical surfaces is effective, the discontinuous crease
which transitions the coaptive surface to the leaflet belly resists
the reverse buckling needed to open the valve. The result is high
opening pressures and high pressure drops across the open
valve.
[0011] In addition to leaflets comprising a single analytical
shape, attempts have been made to improve valve performance by
fabricating leaflets comprising more than one analytical shape. In
this regard, WO 98/32400 provides a valve having leaflets
comprising a cylindrical section and having a spherical coaption
end. The transition from the leaflet belly to the coaption surface
is made by revolving an arc around an axis to form a spherical
coaption area. In addition, the specific shape chosen allows the
surface tangencies at the leaflet free edges to be vertical. The
designers conclude that bidirectional curvature in the leaflet
belly produces poor opening characteristics, and that leaflets with
only one degree of curvature in the belly are superior. Although
the WO 98/32400 valve provides better performance than a fully
spherical leaflet or a fully cylindrical leaflet, the valve has
relatively large gaps at the triple point and the commissure.
[0012] General engineering experience with tissue and polymer heart
valves have established a number of criteria for these valves,
including:
[0013] 1) A coaption surface which extends from the triple point to
the commissure.
[0014] 2) A coaption surface which is tangent to the belly geometry
at its bottom and nearly vertical at its top.
[0015] 3) A simple, singly curved leaflet belly.
[0016] 4) A height short enough to fit into the natural
anatomy.
[0017] 5) A small gap area between leaflets to reduce
regurgitation.
[0018] Cylindrical leaflets with revolved leaflet end sections e.g.
spheres and toroids, produce adequate topological solutions for
only a limited range of valve heights and gap areas. Given the
limitations of existing leaflet geometries, it is desirable to have
a valve leaflet defined by an analytic shape that provides a smooth
transition surface from the leaflet belly to the coaption area, but
which avoid large gaps at the commissures and the triple point.
Analytical shapes suggested in the prior art have not achieved
these goals. Therefore, what is needed is a new valve surface
topology with more degrees of freedom so that a shorter valve with
a small gap area, a cylindrical leaflet, and a tangent coaptive
surface can be produced.
SUMMARY OF THE INVENTION
[0019] It has been discovered that a heart valve with leaflets
having a helical swept coaption surface provides advantages not
obtained from prior art analytical leaflet shapes. In one
embodiment, accordingly, the present invention provides a valve
leaflet having a base portion geometry comprising a cylindrical
section and a top portion geometry comprising a swept helix. To
this end, a heart valve includes a plurality of flexible leaflets.
Each leaflet includes a top portion and a bottom portion. The
bottom portion is a cylinder having an axis, a radius and an axial
section. A first section of the top portion is a surface defined by
a first arc having a first radius swept along a first helix. The
first helix is a right handed helix having the same radius and axis
as the cylinder. A second section of the top portion is a surface
defined by a second arc having a second radius swept along a second
helix. The second helix is a left handed helix having the same
radius and axis as the cylinder.
[0020] A principal advantage of this embodiment is that a leaflet
formed by the combination of a base cylinder geometry and a swept
helical top geometry provide a valve with improved closure
characteristics and which can be made of a small enough size to
provide a good fit into the natural anatomy.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0021] FIG. 1 is a perspective view illustrating an embodiment of a
polymer valve in an open position.
[0022] FIG. 2 is a top view of the polymer valve of FIG. 1.
[0023] FIG. 3 is a perspective view illustrating an embodiment of a
polymer valve in a closed position.
[0024] FIG. 4 is a top view of the polymer valve of FIG. 3.
[0025] FIG. 5 is a perspective view illustrating an embodiment of a
partial valve body and a single leaflet.
[0026] FIGS. 6-11 are perspective views illustrating a method of
forming the leaflet of FIG. 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] A tri-leaflet heart valve prosthesis 10 comprises an
annular, generally cylindrical elastomeric valve body 12 and three
flexible leaflets 14 made of a biocompatible polymer such as
silicone or polyurethane, as shown in FIG. 1. Each leaflet has an
attachment edge by which it is coupled to the valve body along an
attachment curve 16. Each leaflet has a free edge 18 that is not
coupled to the valve body. A sewing ring 20 may be coupled to the
base of the valve body 12 to provide a place for sutures to be
applied when the valve is implanted. The valve body 12 comprises an
annular base 22 and a leaflet support, comprising three shaped
posts 24, that support the leaflets 14.
[0028] When fluid flow is in the forward direction, i.e. in the
direction of the arrow F shown in FIG. 1, the pressure of the blood
flow causes the leaflets 14 to deflect away from a central
longitudinal axis 26 of the valve body that is generally parallel
to the three posts 24. In this "open" position, the leaflets 14
define a large flow orifice, as shown in FIGS. 1 and 2. With the
leaflets in the open position, the valve presents little resistance
to fluid flow.
[0029] When fluid flow is in the reverse direction, i.e. in the
direction of the arrow R shown in FIG. 3, the pressure of the blood
flow causes the leaflets 14 to deflect toward axis 26, as shown in
FIGS. 3 and 4. In this "closed" position, each leaflet would
occlude more than one-third of the valve body's orifice were it not
for the presence of the other leaflets. Consequently, when the
three leaflets deflect toward axis 26, they engage each other and
form coaptive areas along the free edges 18, which help the valve
seal against reverse flow. Further, when the leaflets press
together, each leaflet forms a "triple point" 28 at the point where
the three leaflets come together, as shown in FIG. 4. The place
where the leaflets 14 come together adjacent the posts 24 is called
the "commissure" 30, as shown in FIG. 3.
[0030] Each leaflet 14 of heart valve 10 includes a top portion 32
and a bottom portion 34, FIG. 5. The bottom portion 34 is formed of
a surface 36, see also FIG. 6, defined as a cylinder 38 having an
axis 40, a radius 42 and an axial section 44. A first section A,
FIG. 5, of the top portion 32 is a surface defined by a first arc
46, FIGS. 7 and 10, having a first radius 48 swept along a first
helix 50. The first helix 50 is a right-handed helix having the
same radius 42 and axis 40 as the cylinder 38. A second portion B,
FIG. 5, of the top portion 32 of leaflet 14 is a surface defined by
a second arc 52, FIGS. 8 and 11, having a second radius 54 swept
along a second helix 56. The second helix 56 is a left-handed helix
having the same radius 42 and axis 40 as the cylinder 38.
[0031] The first helix 50 has a pitch P, FIG. 9, and the second
helix 56 has an equal pitch P. Also, the first radius 48 is equal
to the second radius 54. As a result of this construction, the
surface 36 of bottom portion 34 has a curvature C1 defined by
radius 42. However, each of the first section A and the second
section B of the top portion 32 also have the curvature C1 and a
curvature C2 defined by radii 48 and 54, respectively, to improve
coaption at the free edges 18.
[0032] Embodiments of the present invention provide leaflets having
a smooth surface transition between the bottom portion and top
portion thereof. In addition, the edges of the leaflets are
substantially closer to each other when the valve is in the
unloaded ("at rest") position, resulting in a smaller gap between
the leaflets. The valve has improved closure characteristics.
[0033] Although illustrative embodiments have been shown and
described, a wide range of modification change and substitution is
contemplated in the foregoing disclosure and in some instances,
some features of the embodiments may be employed without a
corresponding use of other features. Accordingly, it is appropriate
that the appended claims be construed broadly and in a manner
consistent with the scope of the embodiments disclosed herein.
* * * * *