Title: Value prosthesis for implantation in body channels
Abstract: A valve prosthesis which is especially useful in the case of aortic stenosis and capable of resisting the powerful recoil force and to stand the forceful balloon inflation performed to deploy the valve and to embed it in the aortic annulus, comprises a collapsible valvular structure and an expandable frame on which said valvular structure is mounted. The valvular structure is composed of physiologically compatible valvular tissue that is sufficiently supple and resistant to allow the valvular structure to be deformed from a closed state to an opened state. The valvular tissue forms a continuous surface and is provided with strut members that create stiffened zones which induce the valvular structure to follow a patterned movement in its expansion to its opened state and in its turning back to its closed state.
Patent Number: 6,908,481 Issued on 06/21/2005 to Cribier
| Inventors:
|
Cribier; Alain (Maromme, FR)
|
| Assignee:
|
Edwards Lifesciences PVT, Inc. (Irvine, CA)
|
| Appl. No.:
|
139741 |
| Filed:
|
May 2, 2002 |
Foreign Application Priority Data
| Current U.S. Class: |
623/2.11; 623/904 |
| Intern'l Class: |
A61F 002/24 |
| Field of Search: |
623/111,124,126,211,904,900
606/191,192,194
|
References Cited [Referenced By]
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| 4692164 | Sep., 1987 | Dzemeshkevich et al.
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| 4759758 | Jul., 1988 | Gabbay.
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| 4829990 | May., 1989 | Thuroff et al.
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| 4851001 | Jul., 1989 | Taheri.
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| 5032128 | Jul., 1991 | Alonso.
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| 5037434 | Aug., 1991 | Lane.
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| 5080668 | Jan., 1992 | Bolz et al.
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| 5282847 | Feb., 1994 | Trescony et al.
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| 5360444 | Nov., 1994 | Kusuhara.
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| 5411552 | May., 1995 | Andersen et al.
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| 5500014 | Mar., 1996 | Quijano et al.
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| 5545214 | Aug., 1996 | Stevens.
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| 5571175 | Nov., 1996 | Vanney et al.
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| 5591195 | Jan., 1997 | Taheri et al.
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| 5607464 | Mar., 1997 | Trescony et al.
| |
| 5609626 | Mar., 1997 | Quijano et al.
| |
| 5728068 | Mar., 1998 | Leone et al.
| |
| 5749890 | May., 1998 | Shaknovich.
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| 5840081 | Nov., 1998 | Andersen et al.
| |
| 5855601 | Jan., 1999 | Bessler et al.
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| 5855602 | Jan., 1999 | Angell.
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| 6132473 | Oct., 2000 | Williams et al.
| |
| 6454799 | Sep., 2002 | Schreck.
| |
| 6458153 | Oct., 2002 | Bailey et al.
| |
Primary Examiner: Pellegrino; Brian E
Attorney, Agent or Firm: Hauser; David L., Dippert; William H.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 09/795,803,
filed Feb. 28, 2001, now abandoned, which in turn is a continuation of U.S. patent
application Ser. No. 09/345,824, filed Jun. 30, 1999, now abandoned, which is a
National Phase filing of PCT patent application no. PCT/EP97/07337, filed Dec.
31, 1997 and designating the United States, all of which are incorporated herein
by reference.
Claims
1. A method of implanting a valve prosthesis to treat valvular aortic stenosis,
which comprises the steps of:
(a) advancing a first balloon dilatation catheter having distal and proximal
ends and having a deflated first dilatation balloon adjacent the catheter distal
end into a patient's vasculature to position said first dilatation balloon within
a native stenotic aortic valve and annulus;
(b) inflating said first dilatation balloon to dilate the stenotic aortic valve;
(c) deflating said first dilatation balloon and withdrawing said deflated balloon
in the proximal direction;
(d) advancing a second dilatation catheter having distal and proximal ends and
having a second deflated dilatation balloon adjacent the catheter distal end, wherein
said second balloon has a valve prosthesis arranged circumferentially around said
second dilatation balloon, into the patient's vasculature to position said second
dilatation balloon and said valve prosthesis adjacent to the previously dilated
native stenotic aortic valve;
(e) inflating said second dilatation balloon to cause said valve prosthesis to
adhere to said native aortic valve and annulus; and
(f) deflating said second dilatation balloon and withdrawing said second catheter
in the proximal direction.
2. The method of claim 1, wherein prior to step (a), a guidewire having a distal
end is advanced distally into the patient's vasculature until the guidewire distal
end is adjacent or distal to the native stenotic aortic valve.
3. The method of claim 2, wherein in steps (a) and (d) the first and second balloon
catheters, respectively, are advanced over the guidewire.
4. The method of claim 1, wherein in step (b) the first dilatation balloon is
inflated to a high pressure.
5. The method of claim 4, wherein the first dilatation balloon is inflated maximally
up to the balloon's bursting point.
6. The method of claim 4, wherein the inflation lasts only a few seconds.
7. The method of claim 1, wherein inflating the dilatation balloon in step (b)
tests the native stenotic aortic valve for efficacy of the procedure and creates
an aperture in the native stenotic aortic valve.
8. The method of claim 1, wherein in step (e) the second dilatation balloon is
inflated to a high pressure.
9. The method of claim 8, wherein the second dilatation balloon is inflated to
a pressure less than the pressure to which the first dilatation balloon is inflated.
10. The method of claim 8, wherein the inflation lasts only a few seconds.
11. The method of claim 1, wherein the valve prosthesis needs only a light pressure
for its own expansion.
12. The method of claim 1, wherein the valve prosthesis comprises:
a collapsible, elastic valve member comprised of physiologically acceptable material,
an elastic stent member in which said valve member is mounted, said stent member
having internal and external surfaces, and
a support coupled to the valve member and positioned between the valve member
and the stent member,
wherein said stent member forms a continuous surface and comprises strut members
that provide a structure sufficiently rigid to prevent eversion, wherein the support
extends from the internal surface of the stent member to the external surface of
the stent member, and wherein the stent member has sufficient radial and longitudinal
rigidity to withstand the radial force necessary for implantation, to resist aortic
recoil forces, and to provide long-term support to the valve structure.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a valve prosthesis for implantation in body
channels, more particularly but not only to, cardiac valve prosthesis to be implanted
by a transcutaneous catheterization technique.
The valve prosthesis can be also applied to other body channels provided with
native valves, such as veins or in organs (liver, intestine, urethra . . . ).
The present invention also relates to a method for implanting a valve prosthesis,
such as the valve according to the present invention.
Implantable valves, which will be indifferently designated hereafter
as "IV", "valve prosthesis" or "prosthetic valve", permits the reparation of a
valvular defect by a less invasive technique in place of the usual surgical valve
implantation which, in the case of valvular heart diseases, requires thoracotomy
and extracorporeal circulation. A particular use for the IV concerns patients who
cannot be operated on because of an associated disease or because of very old age
or also patients who could be operated on but only at a very high risk.
Although the IV of the present invention and the process for implanting
said IV can be used in various heart valve diseases, the following description
will first concern the aortic orifice in aortic stenosis, more particularly in
its degenerative form in elderly patients.
Aortic stenosis is a disease of the aortic valve in the left ventricle of
the heart. The aortic valvular orifice is normally capable of opening during systole
up to 4 to 6 cm
2, therefore allowing free ejection of the ventricular
blood volume into the aorta. This aortic valvular orifice can become tightly stenosed,
and therefore the blood cannot anymore be freely ejected from the left ventricle.
In fact, only a reduced amount of blood can be ejected by the left ventricle which
has to markedly increase the intra-cavitary pressure to force the stenosed aortic
orifice. In such aortic diseases, the patients can have syncope, chest pain, and
mainly difficulty in breathing. The evolution of such a disease is disastrous when
symptoms of cardiac failure appear, since 50% of the patients die in the year following
the first symptoms of the disease.
The only commonly available treatment is the replacement of the stenosed aortic
valve by a prosthetic valve via surgery: this treatment moreover providing excellent
results. If surgery is impossible to perform, i.e., if the patient is deemed inoperable
or operable only at a too high surgical risk, an alternative possibility is to
dilate the valve with a balloon catheter to enlarge the aortic orifice. Unfortunately,
a good result is obtained only in about half of the cases and there is a high restenosis
rate, i.e., about 80% after one year.
Aortic stenosis is a very common disease in people above seventy years old
and occurs more and more frequently as the subject gets older. As evidenced, the
present tendency of the general evolution of the population is becoming older and
older. Also, it can be evaluated, as a crude estimation, that about 30 to 50% of
the subjects who are older than 80 years and have a tight aortic stenosis, either
cannot be operated on for aortic valve replacement with a reasonable surgical risk
or even cannot be considered at all for surgery.
It can be estimated that, about 30 to 40 persons out of a million per year, could
benefit from an implantable aortic valve positioned by a catheterization technique.
Until now, the implantation of a valve prosthesis for the treatment of aortic stenosis
is considered unrealistic to perform since it is deemed difficult to superpose
another valve such an implantable valve on the distorted stenosed native valve
without excising the latter.
From 1985, the technique of aortic valvuloplasty with a balloon catheter has
been introduced for the treatment of subjects in whom surgery cannot be performed
at all or which could be performed only with a prohibitive surgical risk. Despite
the considerable deformation of the stenosed aortic valve, commonly with marked
calcification, it is often possible to enlarge significantly the aortic orifice
by balloon inflation, a procedure which is considered as low risk.
However, this technique has been abandoned by most physicians because of
the very high restenosis rate which occurs in about 80% of the patients within
10 to 12 months. Indeed, immediately after deflation of the balloon, a strong recoil
phenomenon often produces a loss of half or even two thirds of the opening area
obtained by the inflated balloon. For instance, inflation of a 20 mm diameter balloon
in a stenosed aortic orifice of 0.5 cm
2 area gives, when forcefully
and fully inflated, an opening area equal to the cross sectional area of the maximally
inflated balloon, i.e., about 3 cm
2. However, measurements performed
a few minutes after deflation and removal of the balloon have only an area around
1 cm
2 to 1.2 cm
2. This is due to the considerable recoil
of the fibrous tissue of the diseased valve. The drawback in this procedure has
also been clearly shown on fresh post mortem specimens.
However, it is important to note that whereas the natural normal aortic
valve is able to open with an orifice of about 5 to 6 cm
2 and to accommodate
a blood flow of more that 15 l/min. during heavy exercise for instance, an opening
area of about 1.5 to 2 cm
2 can accept a 6 to 8 l/min blood flow without
a significant pressure gradient. Such a flow corresponds to the cardiac output
of the elderly subject with limited physical activity.
Therefore, an IV would not have to produce a large opening of the aortic
orifice since an opening about 2 cm
2 would be sufficient in most subjects,
in particular in elderly subjects, whose cardiac output probably does not reach
more than 6 to 8 l/min. during normal physical activity. For instance, the surgically
implanted mechanical valves have an opening area which is far from the natural
valve opening that ranges from 2 to 2.5 cm
2, mainly because of the room
taken by the large circular structure supporting the valvular part of the device.
The prior art describes examples of cardiac valves prosthesis that are aimed
at being implanted without surgical intervention by way of catheterization. For
instance, U.S. Pat. No. 5,411,552 describes a collapsible valve able to be introduced
in the body in a compressed presentation and expanded in the right position by
balloon inflation.
Such valves, with a semi-lunar leaflet design, tend to imitate the natural valve.
However, this type of design is inherently fragile, and such structures are not
strong enough to be used in the case of aortic stenosis because of the strong recoil
that will distort this weak structure and because they would not be able to resist
the balloon inflation performed to position the implantable valve. Furthermore,
this valvular structure is attached to a metallic frame of thin wires that will
not be able to be tightly secured against the valve annulus. The metallic frame
of this implantable valve is made of thin wires like in stents, which are implanted
in vessels after balloon dilatation. Such a light stent structure is too weak to
allow the implantable valve to be forcefully embedded into the aortic annulus.
Moreover, there is a high risk of massive regurgitation (during the diastolic phase)
through the spaces between the frame wires which is another prohibitive risk that
would make this implantable valve impossible to use in clinical practice.
Furthermore, an important point in view of the development of the IV
is that it is possible to maximally inflate a balloon placed inside the compressed
implantable valve to expand it and insert it in the stenosed aortic valve up to
about 20 to 23 mm in diameter. At the time of maximum balloon inflation, the balloon
is absolutely stiff and cylindrical without any waist. At that moment, the implantable
valve is squeezed and crushed between the strong aortic annulus and the rigid balloon
with the risk of causing irreversible damage to the valvular structure of the implantable valve.
SUMMARY OF THE INVENTION
The invention is aimed to overcome these drawbacks and to implant an IV which
will remain reliable for years.
A particular aim of the present invention is to provide an IV, especially aimed
at being used in case of aortic stenosis, which structure is capable of resisting
the powerful recoil force and to stand the forceful balloon inflation performed
to deploy the IV and to embed it in the aortic annulus.
Another aim of the present invention is to provide an efficient prosthesis
valve which can be implanted by a catheterization technique, in particular in a
stenosed aortic orifice, taking advantage of the strong structure made of the distorted
stenosed valve and of the large opening area produced by preliminary balloon inflation,
performed as an initial step of the procedure.
A further aim of the present invention is to provide an implantable valve which
would not produce any risk of fluid regurgitation.
A further aim of the present invention is to provide a valve prosthesis implantation
technique using a two-balloon catheter and a two-frame device.
These aims are achieved according to the present invention which provides a
valve prosthesis of the type mentioned in the introductory part and wherein said
valve prosthesis comprises a collapsible continuous structure with guiding means
providing stiffness and a frame to which said structure is fastened, said frame
being strong enough to resist the recoil phenomenon of the fibrous tissue of the
diseased valve.
The IV, which is strongly embedded, enables the implantable valve to be maintained
in the right position without any risk of further displacement, which would be
a catastrophic event.
More precisely, this valvular structure comprises a valvular tissue compatible
with the human body and blood, which is supple and resistant to allow said valvular
structure to pass from a closed state to an open state to allow a body fluid, more
particularly the blood, exerting pressure on said valvular structure, to flow.
The valvular tissue forms a continuous surface and is provided with guiding means
formed or incorporated within, creating stiffened zones which induce the valvular
structure to follow a patterned movement from its open position to its closed state
and vice-versa, providing therefore a structure sufficiently rigid to prevent diversion,
in particular into the left ventricle and thus preventing any regurgitation of
blood into the left ventricle in case of aortic implantation.
Moreover, the guided structure of the IV of the invention allows the tissue
of this structure to open and close with the same patterned movement while occupying
as little space as possible in the closed state of the valve. Therefore, owing
to these guiding means, the valvular structure withstands the unceasing movements
under blood pressure changes during the heart beats.
More preferably, the valvular structure has a substantially truncated hyperboloidal
shape in its expanded position, with a larger base and a growing closer neck, ending
in a smaller extremity forming the upper part of the valvular structure. The valvular
structure has a curvature at its surface that is concave towards the aortic wall.
Such a shape produces a strong and efficient structure in view of the systolo-diastolic
movement of the valvular tissue. Such a valvular structure with its simple and
regular shape also lowers the risk of being damaged by forceful balloon inflation
at the time of IV deployment.
A trunco-hyperboloidal shape with a small diameter at the upper extremity facilitates
the closure of the valve at the beginning of diastole in initiating the starting
of the reverse movement of the valvular tissue towards its base. Another advantage
of this truncated hyperboloidal shape is that the upper extremity of the valvular
structure, because of its smaller diameter, remains at a distance from the coronary
ostia during systole as well as during diastole, thus offering an additional security
to ensure not to impede at all the passage of blood from the aorta to the coronary ostia.
As another advantageous embodiment of the invention, the guiding means of the
valvular structure are inclined strips from the base to the upper extremity of
the valvular structure with regard to the central axis of the valvular structure.
This inclination initiates and imparts a general helicoidal movement of the valvular
structure around said central axis at the time of closure or opening of said structure,
such a movement enabling to help initiate and finalize the closure of the valvular
structure. In particular, this movement improves the collapse of the valvular structure
towards its base at the time of diastole and during the reversal of flow at the
very beginning of diastole. During diastole, the valvular structure thus fails
down, folding on itself and collapses on its base, therefore closing the aortic
orifice. The strips can be pleats, strengthening struts or thickened zones.
In other embodiments, said guiding means are rectilinear strips from the base
to the upper extremity of the valvular structure. In this case, the guiding means
can comprise pleats, struts or thickened zones. In a particular embodiment, the
stiffened zones then created can be advantageously two main portions, trapezoidal
in shape, formed symmetrically one to each other with regard to the central axis
of the valvular structure, and two less rigid portions separating said two main
portions to lead to a tight closeness in shape of a closed slot at the time of
closure of the upper extremities of the main portions of the valvular structure.
The thickened zones can be extended up to form the stiffened zones.
More particularly, each of said main slightly rigid portions occupy approximately
one third of the circumference of the valvular structure when this latter is in
its open position. The slightly rigid portions maintain the valvular structure
closed during diastole by firmly applying themselves on each other. The closure
of the valvular structure at the time of diastole thus does not have any tendency
to collapse too much towards the aortic annulus.
Preferably, the guiding means are a number of pleats formed within the
tissue by folding, or formed by recesses or grooves made in the tissue. The shape
of the pleats is adapted to achieve a global shape of the desired type for said position.
Alternatively, the guiding means are made of strengthening struts,
preferably at least three, incorporated in the tissue in combination or not with
said pleats.
The guiding means and, in particular, the strengthening struts, help to prevent
the valvular tissue from collapsing back too much and to reverse inside the left
ventricle through the base of the frame, preventing the risk of blood regurgitation.
In a preferred prosthetic valve of the invention, said valvular tissue is made
of synthetic biocompatible material such as TEFLON® or DACRON®, polyethylene,
polyamide, or made of biological material such as pericardium, porcine leaflets
and the like. These materials are commonly used in cardiac surgery and are quite
resistant, particularly to folding movements due to the increasing systolo-diastolic
movements of the valvular tissue and particularly at the junction with the frame
of the implantable valve.
The valvular structure is fastened along a substantial portion of an expandable
frame, by sewing, by molding or by gluing to exhibit a tightness sufficiently hermetical
to prevent any regurgitation of said body fluid between the frame and the valvular structure.
Preferably, an internal cover is coupled or is integral to the valvular
structure and placed between said valvular structure and the internal wall of the
frame to prevent any passage of the body fluid through said frame. Therefore, there
is no regurgitation of blood as it would be the case if there were any space between
the valvular structure fastened on the frame and the zone of application of the
frame on the aortic annulus. The internal cover makes a sort of "sleeve" at least
below the fastening of the valvular structure covering the internal surface of
the frame and thus prevents any regurgitation of blood through the frame.
In the present invention, the frame is a substantially cylindrical structure
capable
of maintaining said body channel open in its expanded state and supporting said
collapsible valvular structure.
In a preferred embodiment of the invention, the frame is made of a material which
is distinguishable from biological tissue to be easily visible by non invasive
imaging techniques.
Preferably, said frame is a stainless metal structure or a foldable plastic
material, made of intercrossing, preferably with rounded and smooth linear bars.
This frame is strong enough to resist the recoil phenomenon of the fibrous tissue
of the diseased valve. The size of the bars and their number are determined to
give both the maximal rigidity when said frame is expanded and the smallest volume
when the frame is compressed.
More preferably, the frame has projecting curved extremities and presents a
concave shape. This is aimed at reinforcing the embedding and the locking of the
implantable valve in the distorted aortic orifice.
In a preferred embodiment of the present invention, the IV is made in two parts,
a first reinforced frame coupled with a second frame which is made of thinner bars
than said first frame and which is embedded inside the second frame. This second
frame to which the valvular structure is fastened as described above, is preferably
less bulky than the first frame to occupy as little space as possible and to be
easily expanded using low pressure balloon inflation.
The present invention also relates to a double balloon catheter to separately
position the first frame in the dilated stenosed aortic valve and place the second
frame that comprises the valvular structure. This catheter comprises two balloons
fixed on a catheter shaft and separated by few centimeters.
The first balloon is of the type sufficiently strong to avoid bursting even at
a very high pressure inflation and is aimed at carrying, in its deflated state,
a strong frame aimed at scaffolding the previously dilated stenosed aortic valve.
The second balloon is aimed at carrying the second frame with the valvular structure.
An advantage of this double balloon catheter is that each balloon has an external
diameter which is smaller than known balloons since each element to be expanded
is smaller.
Moreover, such a double balloon catheter allows to enlarge the choice for
making an efficient valvular structure enabling to overcome the following two contradictory conditions:
- 1) having a soft and mobile valvular structure capable of opening and
closing freely in the blood stream, without risk of being damaged by balloon inflation; and
- 2) needing a very strong structure able to resist the recoil force of
the stenosed valve and capable of resisting, without any damage, a strong pressure
inflation of the expanding balloon.
Furthermore, the shaft of said double balloon catheter comprises two
lumens for successive and separate inflation of each balloon. Of note, an additional
lumen capable of allowing a rapid inflation takes additional room in the shaft.
The invention also relates to a method of using a two-balloon catheter with a
first frame and second frame to which a valve prosthesis of the type previously
described is fastened.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be explained and other advantages and features will appear
with reference to the accompanying schematical drawings wherein:
FIGS. 1
a, 1
b and 1
c illustrate, in section
views, respectively, the normal aortic valve in systole, in diastole and a stenosed
aortic valve;
FIGS. 2
a and 2
b illustrate two examples of a metallic
frame which are combined to a valvular structure according to the present invention;
FIGS. 3
a and 3
b illustrate a frame according to the invention
in its expanded position with an opening out of the extremities, respectively,
with a cylindrical and a concave shape;
FIGS. 4
a and 4
b illustrate an IV of the invention respectively
in its compressed position and in its expanded position in an open position as
in systole;
FIGS. 5
a and 5
b illustrate respectively an IV of the invention
in its closed position and a sectional view according to the central axis of such
a valvular structure which is closed as in diastole;
FIGS. 6
a to 6
d illustrate a sectional view according to
the central axis of an IV according to the present invention and showing the internal
cover and the external cover of the valvular structure overlapping partially or
non overlapping the frame bars;
FIG. 7 illustrates the frontal zig-zag fastening line of the valvular tissue
on the frame;
FIGS. 8
a and 8
b illustrate, respectively, a perspective
view of a valvular structure and an internal cover made all of one piece and a
perspective view of the corresponding frame into which they will be inserted and fastened;
FIGS. 9
a and 9
b illustrate inclined strengthening struts,
an example of a valvular structure according to the invention, respectively in
the open position and in the closed position;
FIGS. 10
a and 10
b illustrate an example of a valvular
structure comprising pleats, respectively in the open and in the closed position;
FIGS. 11
a and 11
b illustrate a valvular structure comprising
two trapezoidal slightly rigid portions, respectively in the open and in the closed position;
FIGS. 11
c to 11
e illustrate a valvular structure comprising
a rectangular stiffened zone, respectively in the open, intermediate and closed position;
FIGS. 12
a and 12
b illustrate, respectively, a perspective
and cross sectional views of an implantable valve in its compressed presentation
squeezed on a balloon catheter;
FIGS. 13
a to 13
l illustrate views of the successive procedure
steps for the IV implantation in a stenosed aortic orifice;
FIG. 14 illustrates an implantable valve made in two parts in its compressed
presentation squeezed on a two-balloon catheter with a reinforced frame on a first
balloon and with the implantable valve on the second balloon; and
FIGS. 15
a to 15
f illustrate the successive steps of the
implantation of the implantation valve in two parts with a two-balloon catheter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the diastole and systole illustrations of section views of FIGS. 1
a and
1b, the arrows A indicates the general direction of the blood flow.
The semi-lunar leaflets
1 and
2 of a native aortic valve (with only
two out of three shown here) are thin, supple and move easily from the completely
open position (systole) to the closed position (diastole). The leaflets originate
from an aortic annulus
2a.
The leaflets
1′ and
2′ of a stenosed valve as illustrated
in FIG. 1
c, are thickened, distorted, calcified and more or less fused,
leaving only a small hole or a narrow slit
3, which makes the ejection of
blood from the left ventricle cavity
4 into the aorta
5 difficult
and limited. FIGS. 1
a to
1c show also the coronary artery
ostium
6a and
6b and FIG. 1
a shows, in particular,
the mitral valve
7 of the left ventricle cavity
4.
An implantable valve according to the invention essentially comprises a supple
valvular structure supported by a strong frame. The positioning of the implantable
valve is an important point since the expanded frame has to be positioned exactly
at the level of the native valvular leaflets
1,
2 of the native valve,
the structures of which are pushed aside by the inflated balloon.
Ideally, the implantable valve is positioned with the fastening line of
the valvular structure on the frame exactly on the remains of the crushed stenosed
valve to prevent any regurgitation of blood. In practice, it is difficult to position
the implantable valve within less than 2 or 3 mm. However, any risk of regurgitation
of blood is eliminated with the presence of an internal cover, as will be described below.
The upper limit of the frame should be placed below the opening of the coronary
arteries, i.e., the coronary ostia
6, or at their level so that the frame
does not impede free blood flow in the coronary arteries. This point is a delicate
part of positioning an IV since the distance between the superior limit of the
leaflets of the natural valve and the coronary ostia
6 is only about 5 to
6 mm. However, the ostia are located in the Valsalva sinus
8 which constitutes
a hollow that are located a little out of the way. This helps to prevent from impeding
the coronary blood flow by the IV.
At the time of implantation, the operator evaluates the exact positioning of
the
coronary ostia by looking at the image produced by a sus-valvular angiogram with
contrast injection performed before the implantation procedure. This image will
be fixed in the same projection on a satellite TV screen and will permit the evaluation
of the level of the origin of the right and left coronary arteries. Possibly, in
case the ostia are not clearly seen by sus-valvular angiography, a thin guide wire,
as those used in coronary angioplasty, is positioned in each of the coronary arteries
to serve as a marker of the coronary ostia.
The lower part of the frame of the IV preferably extends by 2 or 3 mm inside
the left ventricle
4, below the aortic annulus
2a. However,
this part of the frame should not reach the insertion of the septal leaflet of
the mitral valve
7, so that it does not interfere with its movements, particularly
during diastole.
FIGS. 2
a and
2b show respectively an example of a cylindrical
frame or stent
10 comprising intercrossing linear bars
11, with two
intersections I by bar
11, the bars
11 being soldered or provided
from a folded wire to constitute the frame, with for instance a 20 mm, 15 mm or
12 mm height, and an example with only one intersection of bars
11. Preferably,
such a frame is expandable from a size of about 4 to 5 millimeters to a size of
about 20 to 25 mm in diameter, or even to about 30-35 mm (or more) in particular
cases, for instance for the mitral valve. Moreover, said frame, in its fully expanded
state, has a height of approximately between 10 and 15 mm and in its fully compressed
frame, a height of approximately 20 mm. The number and the size of the bars are
adapted to be sufficiently strong and rigid when the frame is fully open in the
aortic orifice to resist the strong recoil force exerted by the distorted stenosed
aortic orifice after deflation of the balloon used in the catheterization technique
which has been previously maximally inflated to enlarge the stenosed valve orifice.
The frame may have several configurations according to the number of bars
11
and intersections. This number, as well as the size and the strength of the bars
11, are calculated taking into account all the requirements described, i.e.,
a small size in its compressed form, its capacity to be enlarged up to at least
20 mm in diameter and being strong when positioned in the aortic orifice to be
able to be forcefully embedded in the remains of the diseased aortic valve and
to resist the recoil force of the aortic annulus. The diameter of the bars is chosen,
for instance, in the range of 0.1-0.6 mm.
A frame particularly advantageous presents, when deployed in its expanded state,
an opening out
12 at both extremities as shown in FIGS. 3
a and
3b,
the frame having a linear profile (FIG. 3
a) or a concave shape profile (FIG.
3
b). This is aimed at reinforcing the embedding of the IV in the aortic
orifice. However, the free extremities of the openings
12 are rounded and
very smooth to avoid any traumatism of the aorta or of the myocardium.
The structure of a preferred frame used in the present invention both maintains
the aortic orifice fully open once dilated and produces a support for the valvular
structure. The frame is also foldable. When folded by compression, the diameter
of said frame is about 4 to 5 millimeters, in view of its transcutaneous introduction
in the femoral artery through an arterial sheath of 14 to 16 F (F means French,
a unit usually used in cardiology field) i.e., about 4.5 to 5.1 mm. Also, as described
below, when positioned in the aortic orifice, the frame is able to expand under
the force of an inflated balloon up to a size of 20 to 23 mm in diameter.
The frame is preferably a metallic frame, preferably made of steel. It constitutes
a frame with a grate type design able to support the valvular structure and to
behave as a strong scaffold for the open stenosed aortic orifice.
When the frame is fully expanded, its intercrossing bars push against the remains
of the native stenosed valve that has been crushed aside against the aortic annulus
by the inflated balloon. This produces a penetration and embeds the bars within
the remains of the stenosed valve, in particular owing to a concave profile of
the frame provided with an opening out, as illustrated in FIG. 3
b. This
embedding of the frame on the aortic annulus, or more precisely on the remains
of the crushed distorted aortic valve, will be determinant for the strong fixation
of the IV in the right position, without any risk of displacement.
Moreover, the fact that the valve leaflets in degenerative aortic stenosis
are grossly distorted and calcified, sometimes leaving only a small hole or a small
slit in the middle of the orifice, has to be considered an advantage for the implantation
of the valve and for its stable positioning without risk of later mobilization.
The fibrous and calcified structure of the distorted valve provides a strong base
for the frame of the IV and the powerful recoil phenomenon that results from elasticity
of the tissues contribute to the fixation of the metallic frame.
The height of the fully expanded frame of the illustrated frames
10 is
preferably between 10 and 15 mm. Indeed, since the passage from the compressed
state to the expanded state results in a shortening of the metallic structure,
the structure in its compressed form is a little longer, i.e., preferably about
20 mm length. This does not constitute a drawback for its transcutaneous introduction
and its positioning in the aortic orifice.
As mentioned above, the frame is strong enough to be able to oppose the powerful
recoil force of the distended valve and of the aortic annulus
2a.
Preferably it does not possess any flexible properties. When the frame has reached
its maximal expanded shape under the push of a forcefully inflated balloon, it
remains substantially without any decrease in size and without any change of shape.
The size of the bars that are the basic elements of the frame is calculated in
such a way to provide a substantial rigidity when the frame is fully expanded.
The size of the bars and their number are calculated to give both maximal rigidity
when expanded and the smallest volume when the metallic frame is its compressed position.
At the time of making the IV, the frame is expanded by dilatation to its broadest
dimension, i.e., between 20 mm and 25 mm in diameter, so as to be able to fasten
the valvular structure on the inside side of its surface. This fastening is performed
using the techniques in current use for the making of products such as other prosthetic
heart valves or multipolars catheters etc. Afterwards, it is compressed in its
minimal size, i.e., 4 or 5 mm, in diameter in view of its introduction in the femoral
artery. At time of the IV positioning, the frame is expanded again by balloon inflation
to its maximal size in the aortic orifice.
If the frame is built in an expanded position, it will be compressed, after fastening
the valvular structure, by exerting a circular force on its periphery and/or on
its total height until obtaining the smallest compressed position. If the frame
is built in its compressed position, it will be first dilated, for instance, by
inflation of a balloon and then compressed again as described above.
To help localizing the IV, the frame being the only visible component of the
valve,
the shaft of the balloon catheter on which will be mounted the IV before introduction
in the body (see below) possesses preferentially metallic reference marks easily
seen on fluoroscopy. One mark will be at level of the upper border of the frame
and the other at the level of the lower border. The IV, when mounted on the catheter
shaft and crimpled on it, is exactly positioned taking into account these reference
marks on the shaft.
Accordingly, the frame is visible during fluoroscopy when introduced
in the patient's body. When the frame is positioned at the level of the aortic
annulus, the upper border of the frame is placed below the coronary ostia. Furthermore,
the implanting process during which the balloon inflation completely obstructs
the aortic orifice, as seen below, is performed within a very short time, i.e.,
around 10 to 15 seconds. This also explains why the frame is clearly and easily
seen, without spending time to localize it. More particularly, its upper and lower
borders are clearly delineated.
FIGS. 4
a and
4b show an example of a preferred IV
13
of the present invention, respectively in its compressed position, in view of its
introduction and positioning in the aortic orifice, and in its expanded and opened
(systole) position. FIGS. 5
a and
5b show the expanded position
of this example closed in diastole, respectively in perspective and in a crossed
section view along the central axis XX of the valve prosthesis.
The valvular structure
14 is compressed inside the frame
10 when
this is in its compressed position (FIG. 4
a), i.e., it fits into a 4 to
5 mm diameter space. On the other hand, the valvular structure can expand (FIG.
4
b) and follow the frame expansion produced by the inflated balloon. It
will have to be able to reach the size of the inside of the fully deployed frame.
The illustrated IV
13 is made of a combination of two main parts:
- 1) the expandible but substantially rigid structure made of the frame
10, a metallic frame in the example; and
- 2) a soft and mobile tissue constituting the valvular structure 14
exhibiting a continuous surface truncated between a base 15 and an upper
extremity 16; the tissue is fastened to the bars 11 of the frame
at its base 16 and is able to open in systole and to close in diastole at
its extremity 16, as the blood flows in a pulsatile way from the left ventricle
towards the aorta.
The tissue has rectilinear struts
17 incorporated in it in plane including
the central axis XX, in order to strengthen it, in particular, in its closed state
with a minimal occupation of the space, and to induce a patterned movement between
its open and closed state. Other examples of strengthening struts are described
below. They are formed from thicker zones of the tissue or from strips of stiffening
material incorporated in the tissue; they can also beglued or soldered on the valvular tissue.
These strengthening struts help to prevent the valvular tissue from collapsing
back too much and to evert inside the left ventricle through the base of the frame.
These reinforcements of the valvular tissue help maintain the folded tissue above
the level of the orifice during diastole, prevent too much folding back and risk
of inversion of the valvular structure inside the left ventricle. By also preventing
too much folding, a decrease of the risk of thrombi formation can also be expected
by reducing the number of folds.
The truncated shape forming a continuous surface enables to obtain a strong structure
and is more efficient for the systolo- diastolic movements of the valvular tissue
during heart beats. The truncoidal shape facilitates the closure of the valve structure
at the beginning of diastole in facilitating the start of the reverse movement
of the valvular tissue towards its base at the time of diastole, i.e., at the time
of flow reversal at the very beginning of diastole. During diastole, the valvular
structure
14 thus fails down, folding on itself, thereby collapsing on its
base, and therefore closing the aortic orifice. In fact, the valvular structure
has preferably, as illustrated, an hyperboloid shape, with a curvature on its surface
concave towards the aortic wall that will contribute to initiating its closure.
Moreover, the basis of the truncated hyperboloid is fixed on the lower
part of a frame and the smallest extremity of the truncated hyperboloid is free
in the blood stream, during the respected closing and opening phasis.
An important advantage of this hyperboloidal shape is that the upper extremity
16 of the valvular structure
14 can remain at a distance from the
coronary ostia during systole as well as during diastole, because of its smaller
diameter, thus offering an additional security to make certain that the passage
of blood from aorta to the coronary ostia is not impeded.
The base
15 of the truncated tissue is attached on the frame
10
along a line of coupling
18 disposed between the inferior fourth and the
third fourth of the frame in the example. The upper extremity
16, with the
smaller diameter, overpasses the upper part of the frame by a few millimeters;
6 to 8 mm, for instance. This gives the valvular structure a total height of about
12 to 15 mm.
The upper extremity
16 of the truncated tissue, i.e., the smaller diameter
of the hyperboloidal structure
14, is about 17 to 18 mm in diameter (producing
a 2.3 to 2.5 cm
2 area opening) for a 20 mm diameter base of the truncated
structure, or 19 to 20 mm in diameter (producing a 2.8 or a 3 cm
2 area
opening) for a 23 mm diameter base. An opening area around 2 cm
2 or
slightly above, gives satisfactory results, particularly in elderly patients who
would not reasonably need to exert high cardiac output.
For instance, in the present example, the line of fastening of the base of the
truncated tissue on the frame will have to expand from a 12.5 mm perimeter (for
a 4 mm external diameter of the compressed IV) to a 63 mm perimeter (for a 20 mm
external diameter of the expanded IV), or to a 72 mm perimeter (for a 23 mm external
diameter, in case a 23 mm balloon is used).
Another advantage of this truncated continuous shape is that it is stronger
and has less risk of being destroyed or distorted by the forceful balloon inflation
at the time of IV deployment. Also, if the truncated hyperboloidal shape is marked,
for instance, with a 16 or 17 mm diameter of the upper extremity as compared to
a 20 mm diameter of the base (or 18 to 20 mm for 23 mm), the smaller upper part
is compliant during balloon inflation in order to enable the balloon to expand
cylindrically to its maximal mm diameter (or 23 mm). This is made possible by using
a material with some elastic or compliant properties.
The valvular structure of the invention, as shown in the illustrated example,
includes advantageously a third part, i.e., the internal cover
19 to be
fixed on the internal wall of the frame
10. This internal cover prevents
any passage of blood through the spaces between the bars
11 of the frame
in case the implantable valve would be positioned with the fastening line of the
valvular structure on the frame not exactly on the remains of the dilated aortic
valve, i.e., either above or below. It also strengthens the fastening of the valvular
structure
14 to the frame
10.
In the different sectional views of the different examples of IV according to
the invention, as illustrated at FIGS. 6
a to
6c, the internal
cover
19 covers the totality of the internal side of the frame
10
(FIG. 6
a), only the lower part of the frame
10 (FIG. 6
b),
or it can additionally cover partially 3 to 5 mm as shown in the passage of blood
from aorta to the coronary ostia FIG. 6
c, the upper part defined above the
coupling line
18 of the valvular structure.
For instance, such an extension of the internal cover
19 above the fastening
line
18 of the valvular structure will give another security to avoid any
risk of regurgitation through the spaces between the bars
11 in case the
IV would be positioned too low with respect to the border of the native aortic valve.
The internal cover can also be molded to the valvular structure or casted to
it which therefore constitutes an integral structure. The valvular structure and
the internal cover are therefore strongly locked together with minimum risk of
detachment of the valvular structure which is unceasingly in motion during systole
and diastole. in that case, only the internal cover has to be fastened on the internal
surface of the frame which renders the making of the IV easier and makes the complete
device stronger and more resistant. In particular, the junction of the mobile part
of the valvular structure and the fixed part being molded as one piece is stronger
and capable to face the increasing movements during the systolo-diastolic displacements
without any risk of detachment.
The presence of the internal cover makes an additional layer of plastic material
that occupies the inside of the frame and increases the final size of the IV. Therefore,
in the case in which the internal cover is limited to the inferior part of the
frame (that is, below the fastening line of the valvular structure), it does not
occupy any additional space inside the frame. Here also, it is more convenient
and safer to make the valvular structure and this limited internal cover in one piece.
In other aspects, to prevent any regurgitation of blood from the aorta towards
the left ventricle during diastole, the base of the valvular structure is preferably
positioned exactly at the level of the aortic annulus against the remains of distorted
stenosed valve pushed apart by the inflated balloon. Therefore, there is no possibility
of blood passage through the spaces between the metallic frame bars
11 below
the attachment of the valvular structure.
However, to avoid any risk of leaks,
