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PROSTHETIC HEART VALVE
FIELD OF THE INVENTION
The present invention relates to mechanical heart
valve prostheses and, in particular, to improved
prosthetic heart valves having valve members or occluders
which both pivot and translate in moving between their
open and closed, positions.
BACKGROUND OF THE INVENTION
A wide variety of heart valve prostheses have been
developed which operate hemodynamically, in conjunction
l0 with the pumping action of the heart, to take the place
of a defective natural valve. These valves have
generally been designed to function with valve members in
the form of a single occluder, a pair of occluders or
leaflets or even three or more occluders; such occluders
pivot along eccentric axes (or both pivot and translate)
to open and close a central blood flow passageway through
a generally annular valve body within which the occluders
are usually appropriately supported.
U.S. Patent No. 4,689,046 (August 25, 1987)
discloses a bileaflet heart valve having a pair of flat
leaflets with ears of generally trapezoidal configuration
extending from the flat lateral surfaces thereof. The
ears have flat end faces and are received in
diametrically opposed recesses in the valve body having
facing flat end surfaces; the recesses are shaped so that
the ears are rockingly engaged therein by tapered recess
guide wall surfaces of arcuate configuration.
U.S. Patent No. 5,137,532 (August 11, 1992)
discloses bileaflet heart valves having pivot
arrangements which allow the leaflets to assume an
orientation substantially parallel to the centerline
through the valve in their open position in a valve body
which is elongated in axial length relative to bileaflet
valves of earlier design wherein designers generally
attempted to minimize the length of the blood flow path
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through the valve body, because the valve was felt to be
confining. In one embodiment, camming surfaces provided
on the leaflets engage appropriately located projections
extending radially inward from the valve body sidewall,
and the upstream displacement of the leaflets which
occurs upon the reversal of blood flow causes prompt
pivoting of the leaflets toward the closed positions.
U.S. Patent No. 5,314,467 (May 24, 1994) discloses a
bileaflet heart valve wherein leaflets of composite
curvature are supported by laterally extending elongated
ears which are received in recesses formed in
diametrically opposed flat wall sections of the interior
surface of a valve body that is formed with a flared
outflow seat region against which the leaflet downstream
edges seat. The recesses each have a serpentine guide
wall along the upstream edge thereof. The combination of
it and a second downstream wall creates a sequence of
rotational and then translational movement of the
leaflets as they pivot from the open position to the
closed position.
More recently, attention has also begun to be given
to trileaflet valves, and the study of blood flow through
such multiple leaflet valves has convinced many
investigators that it is very important that emphasis
should be given to achieving designs with minimum
turbulence and minimum pressure drop. It was generally
believed that the shorter the axial length of a valve
body was, the less would be the resistance to blood flow
through the critical region of the valve, because the
valve body was of course the region of greatest
constriction. Many patented valve designs also
concentrated on the shape and the placement of the
occluders to minimize pressure drop and turbulence.
A number of U.S. patents, such as Nos. 4,363,142,
4,328,592, 5,178,632 and 5,171,623 illustrate heart
valves having relatively short valve bodies of generally
circular cross-section, some of which have rounded or
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radially outwardly flared upstream and downstream ends.
U.S. Patent No. 4,775,378 shows a heart valve having a
single occluder with a shallow S-shaped curvature that is
alleged to promote the formation of a stable closed
vortex on the suction side of the occluder; .it is
employed in combination with a valve body having a
circular cross-section passageway that is continuously
and increasingly constricted, i.e. its diameter
decreasing, in the downstream direction. U.S. Patent No.
4,846,830 discloses a bileaflet valve having a similar
valve body wherein a pair of curved leaflets are employed
which are arranged to create a venturi tube nozzle in the
direction of downstream flow which is alleged to avoid
vortex formation. U.S. Patent No. 4,995,881 shows a
valve having a similarly sloping entrance in combination
with a pair of leaflets that are curved in the downstream
direction so as to define a nozzle-shaped passage
centrally between the two leaflets when they are in their
open position orientation.
The more that such. mechanical prosthetic valves have
been studied, the more that investigators have concluded
that the ideal prosthetic valve simply does not yet
exist. From a materials standpoint, pyrolytic carbon has
been determined to be adequately nonthrombogenic; as a
result, the problem of combatting thrombosis in
mechanical valves is presently felt to lie in preventing
excess turbulence, high shear stresses and local regions
of stasis. Blood is a very delicate tissue, and even
minor abuses caused by turbulence and high shear stress
can cause either thrombosis or emboli generation at local
regions of stagnation. Therefore, it is felt that future
improvement in the characteristic of thromboresistance in
mechanical valves will likely be attained through the
achievement of smooth, nonturbulent flow and the absence
of stasis.
The search continues for improved mechanical heart
valve prostheses that provide passageways through which
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blood will flow freely and with a minimum of drag in the
open position, which will close quickly upon the
occurrence of backflow to minimize regurgitation of
blood, and which can be efficiently manufactured and
assembled. Accordingly, new valve designs incorporating
such features have continued to be sought.
SUMMARY OF THE INVENTION
The present invention provides bileaflet mechanical
heart valve prostheses having the aforementioned
desirable characteristics wherein leaflets can assume an
orientation in the open position where they are parallel
to the longitudinal axis of the valve passageway but will
still promptly close, with guidance and control of the
leaflets being accomplished solely by contact between
laterally protruding ears and complementary-shaped
cavities in the sidewalls of the valve body in which they
are received which have straight camming edges that are
angularly located to achieve prompt pivoting, thus easing
manufacturing requirements because the most critical
tolerances to be maintained are substantially confined to
a single region of the valve body.
Because turbulence in mechanical heart valves can
damage blood and lead to clotting, such sources which
exist both at the leading edges of leaflets that are
inclined to the direction of blood flow and at the
leading edge of the valve body orifice itself should be
taken into consideration. When a liquid must pass around
a corner, as when entering an orifice, separation occurs,
and turbulence and elevated shear stresses are created in
such zone of separation. By selecting a valve body of
relatively extended axial length, by mounting leaflets
therein so that, in their open orientation, the leaflets
are individually free to generally follow blood flow and
orient themselves so as to be parallel to the direction
of downstream blood flow at any instant (to minimize the .
turbulence associated with the leaflets), and by also
contouring the orifice inlet to eliminate that usual zone
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of separation that would otherwise be present, both head
or pressure loss and the tendency for thrombosis
generation are concomitantly decreased.
The leaflets preferably have rectilinear surfaces
that will assume an orientation in alignment with the
instantaneous direction of blood flow iin the full open _
position, such as substantially parallel to the
centerline through the valve, e.g. about 2° or less
therefrom, thereby minimizing resistance to the
downstream flow of blood; such rectilinear leaflet
surfaces can be flat or cylindrical. The leaflets should
be parallel when blood flow is at its highest level;
however, when the velocity of the downstream blood flow
slows near the end of the pumping stroke, they may
undergo a prerotation toward their closed orientation
from such parallel orientation.
More specifically, it has been found that the
entrance at the upstream end of the valve body should be
essentially a section of a torus having a radius of
curvature which is at least about 28% of the radius of
the central passageway through the valve body and not
greater than about 80%, that the valve body should have
an average axial length at least about equal to the
central passageway radius, and that the flaring toroidal
entrance section should extend circumferentially about
the opening but preferably does not extend axially a
distance greater than about one-third of the average
axial length of the valve body. Preferably the surface
is at least about 300 of a quadrant of a torus which at
its downstream end is preferably tangent to the remainder
of the interior surface, which is preferably generally
cylindrical.
Because the flow through such a valve body has been
found to be a function of the fourth power of its
diameter, the diameter of the passageway through such a
valve body is maximized by using the thinnest valve body
wall that is structurally adequate, in addition having
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the average axial length of the valve body be equal to at
least about the radius of the interior cross-section.
The interior diameter is preferably advantageously
maximized by allowing the exterior surface of the valve
body to interface directly with the raw edge of the
tissue annulus from which the natural valve has been
excised, and suture rings are preferably employed which
permit both mitral valves and aortic valves to be so
located that the raw tissue annulus interfaces directly
with the pyrocarbon outer surface of the valve body. The
mitral valve suture ring may be a fairly straightforward
design: however, for a replacement aortic valve, a suture
ring is designed to permit the valve to be located above
the aortic annulus in a location so that its upstream
flared entrance will be slipped into the aortic orifice
region so that its outer wall surface, which is concave
and toroidal, interfaces directly with the raw edge of
the tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a bileaflet heart
valve embodying various features of the present
invention, shown with the leaflets in the open position.
FIG. 2 is a sectional view taken generally along the
line 2-2 of FIG. 1 showing the leaflets in the full open
position, and with a suture ring attached to the valve
body.
FIG. 2A is a sectional view taken generally along
the line 2-2 of FIG. 1 showing the leaflets in the full
open position, and with an alternative suture ring
attached to the valve body.
FIG. 3 is a view similar to FIG. 2 showing the
leaflets in their prerotation orientation as they would
be when the downstream flow of blood slows prior to
reversal.
FIG. 3A is a fragmentary sectional view taken along
the lines 3A-3A of FIG. 3.
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FIG. 4 is a view similar to FIG. 2, showing the
leaflets in elevation and in their closed position, with
the suture ring omitted.
' FIG. 5 is a plan view looking downward at the valve
shown in FIGS. 1 and 2 with the leaflets in the full open
position.
FIG. 6 is a vertical sectional view through the
valve taken generally along the line 6-6 of FIG. 2 with
the leaflet in the full open position.
FIG. 7 is a perspective view of a leaflet from the
valve of FIG. 1.
FIG. 8 is a side elevation view, reduced in size, of
the leaflet of FIG. 7.
FIG. 9 is a front view of the leaflet of FIG. 8.
FIG. 10 is a fragmentary sectional view, enlarged in
size, taken generally along the line 10-10 of FIGS. 5 and
6 with the sewing ring removed, showing the location of
the ear in the cavity in the valvt~ hnAv cirlAwall crhcn i-7~,c
_ __ _ - - j __- __-. _ ,. . . .~ ~... j "..~...."....~r..v ..aav.aa.w..
leaflet is in its full open position.
FIGS. 10A through lOD are full sectional views
similar to FIG. 10 with the right-hand leaflet omitted
and with the left-hand leaflet shown respectively (A) in
the prerotation position, (B) at the beginning of closing
movement, (C) in an intermediate position during closing
movement and (D) in its full closed position.
FIGS. 11 and 12 are fragmentary horizontal sectional
views taken respectively along the lines 11-11 and 12-12
of FIG. 3, with the leaflets removed.
FIG. 13 is a fragmentary sectional view taken
generally along the line 13-13 of FIG. 2A.
FIG. 14 is a fragmentary sectional view, enlarged in
size, illustrating the valve body wall structure.
FIG. 15 is a view similar to FIG. 14 showing the
aortic sewing ring attached.
FIG. 16 is a sectional view similar to FIG. 2 of an
alternative embodiment of a bileaflet heart valve
embodying various features of the invention shown with
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the leaflets in the open position and with a suture ring
attached that is designed to facilitate mounting of the
valve in the aortic position.
FIG. 17 is a vertical sectional view taken through
the valve. and through one of the leaflets along the line
17-17 of FIG. 16. '
FIGS. 18A through 18D are sectional views similar to
FIGS. 10A through lOD with the right-hand leaflet omitted
to show'the details of the cavities, which details are
omitted from each left-hand cavity, and with the section
through the leaflet ear showing the left-hand leaflet,
respectively, (A) in the fully open position, (B) at the
beginning of closing movement, (C) in an intermediate
position during closing movement, and (D) in the fully
closed position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Illustrated in FIG. 1 is a prosthetic heart valve 11
constructed so as to embody various features of the
present-invention. Very generally, heart valves having
this construction have improved flow characteristics,
particularly when the valve is in its fully open
position, because the leaflets can align parallel to the
valve centerline or can align at slight deviations
thereto depending upon instantaneous variations in the
blood flow path through the valve, whichever is the low
energy orientation. As a result, these orientations
minimize the resistance to blood flow and substantially
reduce boundary layer separation along major surfaces of
the leaflets. The valve design also provides good
washing characteristics which guard against the
occurrence of stagnation and potential clotting.
Importantly, although heart valves of this design exhibit
a rapid response to change in the direction of blood,
both in respect of opening and closing, the final
movement of the closing leaflets is one almost solely of
rotation so that there is relatively low wear due to the
leaflet rubbing against a fulcrum within the valve body
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at about the time of complete closing, thus eliminating
potential problems which could result from the creation
of regions of substantial wear on the leaflet and on the
' fulcrum by translation movement during the final closing
phase when the pressure across the valve is building to
the maximum value.
Heart valve 11 includes a generally annular valve
body 13 which carries a pair of pivoting occluders or
leaflets 15 that alternately open and close either to
l0 allow the smooth flow. of blood in the downstream
direction, as indicated by the arrow A in FIG. 2, or to
prevent any substantial backflow of blood, i.e.
regurgitation. The valve body 13 defines a blood flow
passageway in the form of its generally arcuate, mostly
cylindrical interior wall surface 17. The valve body 13
has a curved entrance region 19 at its upstream end,
which has been found to substantially increase
streamlined flow characteristics through the valve with
low turbulence and substantially no generation of
thrombosis. The details of the curved entrance region 19
which extends axially for a distance not greater than
about one-third of the average axial length of the valve
body are discussed hereinafter along with the operation
of the valve. A pair of diametrically opposed, thickened
wall sections 21, as best seen in FIG. 5, protrude inward
from an otherwise right circular cylindrical surface,
creating what is referred to as a tabulated cylindrical
surface as a result of the thickened sections 21
terminating in facing, parallel flat wall surfaces 23 in
which pairs of cavities or recesses 25 are formed that
function as one-half of the pivot arrangement which
controls the opening and closing movements of the
leaflets 15. Thus, the interior surface downstream of
the curved entrance region 19 is generally rectilinear.
The valve body 13 preferably has a scalloped
downstream profile so that there are, in effect, a pair
of shallow notches 27 formed in the contour of the valve
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body 13 .in the regions ju.~t dcjwnst:rearn c:>i~ t:he thickened wall
sections 21. In a bileaflet valve cf this type, the side
openings provided by these r~.Wr.:anea 2'? arw~ <rligned w.th the
central passageway between the 7.eaf.Let;~ a.5 so that, upon
reversal of blood fa..ow, backtlowirr~ i~.~.ooc: ~waterally enters the
valve body through these ;side ca~.,er~airnc~:s c:li r~~c:ting a ->urge of
blood flow into the central passageway rwgion and creating
forces which impinge--v upon tine lea lE~l:: cut: fa_ow su:r. fa~.~:e:~, the
effect of which is to further enziance prompt pivoting of the
eccentrically mounted leaflets toward timir closed position
orientations. This func~tLora i~~ desc::a::Gk~ed i.n g:reai~er cletai_1 in
U.S. Patent No. 5,308,361.
The exterioa:~ surfa.~e of t:L~E-~ re:l.;:rt _i.ve:~l.~~ thin va:l.ve~ body 13
in the region downstream of the f..lared entrance section 19 is
substantially that of a surface of <~ r:ic)r,.t: circular cylinder
except for a slic~ht~.y tk~ic:keneca c.~ent:z:~.~jl ~~~.:~c~t:ion wheo-eir a
shallow groove 29 i:~ formed bet:ween ~~. pai.r of raised bands 29a.
A metal stiffening attawhmenE: r.:i~ c~ :;W ~>f i.~rui.r~uae ca.e,_:_gn. (FIG.
2)
which is formed with a plural.it.y of s.~.~ rc:umferenti.al_iy spaced
apart inwardly protruding fingers 3()a is mated therE~with to add
stability and rigidity t~.> t:he vs.3_~re k:,~ctciy . 'Che valv~E..~ body
itself is preferably made of a suitable material, such as
pyrocarbon or pyx°ocarbo;u-c;c.oatv.~zc:°i ~: ra~>f,~ t~:., ~~:~
i:~ wel _: known m
this art, which has suff3_c:iel~t. r.F~si~.i~:ncy that it can be
deformed so as to permit the i.r~~4~ertic~r: of the pair of leaflets
15 in their operative lc>>c~~ti~.~n;:,. r'ruEe rr~E:t.ai r~i.ng ~3Q is also
used to support the sewing ring of appropriate design, as
broadly l~,nown in th~..s a:et. i~c~i::.t~ ~.=~ec;i c~xarri.p:i..es of ~ewir~g
or
suture rings which can be employed are described in U.S.
Patents Nos. 4, 535, 483 anci 5, l'lF3r C~~3~-.
The thickened exte:ri.c.~r x>arac~.s ?9sc tax°e :~t.rat:egi.c~lly
located
in the downstream cylindrical ser_tion c,f the valve L.~ody spaced
from the flared e~ntx ance ~~ecl:: ic.>rn 1..9. ~.~ ~-'xplai.nE'<a r:~ereinaf
tez
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in detail, the shallow groocre .~''~ is locat:.ed to accommodate the
inwardly protrud:irncl fingers :3~i~j ot~ ttm:e mE='tai ring 3~) in either
orientation as e:~plained tier°einaft:e:c " ~t'he groovf= v?~-~, which
i5
of arcuate cross sec:.tion ;end t'ar~stitui:es the narr_ovacast diameter
on the exterior surface .is locat=ed sc> t:t-i~.t it is conlpl.etel~.%
dc:>wnstream of the fulcrums wta:c.c::~u ~-~.rc~ rror.z;~ec ~_n recea.sses
2r,.
This arrangement ~>ermit~ a °~~ue E,.z~:~zre i.rrc~: t:o be
~~c<:~~mmodated in
a location where the remaining t.a_ssue r.~r~n~ulus ~,ai:L1 :~e in
contact with a portion of the right c.:~rcular cylindrical
exterior surface of the v~:~:l..v~3 ):)c>d"~.
The leaflets 7_.'::~ are prefet:'~.~~:>l.y :i_c~er,t:ic.:al in ;~havcpe arid
size. Each leaflet has two reu~t;i.line:-rr, prefe.rabl~,% flat,
surfaces, i.e. an inflow surface ~1 arac~ ~sn outflow :,urface 33,
and the leaflet ~_s L~referabl~T c>.f~~ub~l.::ar~t i.~u l 1y corm ant
thickness such that the ;~l,rrt ~c ~a, -..L ~z~.ca , 3 are p<.~ra:l. lel to
each
other. The inflow surface 31. is arb:at:r°ari.ly def.i.nec~. as the
surface which faces upstream with the leaflets irr t2re closed
position (see FIC~. ~~?, ~~tuE'rea~tl:~e cac~t,f:Lo~~r :~ur:i-acc~ .:3 faces
downstream. Altriouc~h the leC~f J..W : ''. ': ax-e p:ref_carak~l.~; f.7.at,
other configurations, s~lch a~ ~>ectiora~~ of taollow cy:L i.n.ders of
circular of elliptical cross sec:t,~on, can alternatively be
employed, as discussed .irr moxw caetai. 1. i.r, i:l.:~ . Pat:.ent:
No. 5, 24E>, 453.
The leaflets 15 each have ~_r maj~.~~xv ar~,cuate edge surfa ~e 35,
which is located at the downstream edge of the leaf~.et in the
open position, arid each has <.r rrvinc:r rr~.~~tin~:~ edge surt'ace 3-7
which is located at the cy>pou.t;c.,. up=;t: x:ea:rn. edgF~ c>f t:he leaflet:
in the open positioro. 'rhe arr~u..rrate e~ic~e s,.z:rfa.r.e 35 l.~r_eferably
has a configuration such as to abut and seat: cl.osel5% against
the cylindrical sidewal:L irrte.rior surface 1'7 of true valve body
in the closed pos~iti.on. 'l:'he m..:ir~or ~:~ic~e surfaced 3'i ~.s
preferably
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flat and formed at an angle so as to mate flush against
the corresponding mating edge surface 37 of the opposing
leaflet in the closed position, as best seen in FIG. 4.
As a result, the minor edge surface 37 is accordingly
oriented at an angle to the inflow surface 31 which is
substantially the same as the downstream angle which the
outflow surface 33 forms with the centerline plane in the
closed position, and it is preferably an angle between
about 30° and about 60°. The centerline plane is defined
l0 as a plane which includes the centerline of the
passageway and which is parallel to the pivot axes of the
leaflets; in the illustrated embodiment, it is
perpendicular to the flat wall surfaces 23 of the valve
body passageway. The angle in question defines the
extent of the angular rotation that each leaflet 15 will
undergo in moving from the fully open position to the
fully closed position. This is taken into consideration
because there may be an advantage in having a smaller
angle, as opposed to a larger angle, because the leaflets
need not rotate as great an angular distance in order to
reach the fully closed position. As illustrated in FIG.
4, this angle is about 50° in the preferred embodiment.
As best seen in FIG. 7, the leaflets 15 each have a
pair of intermediate straight edge regions 39 located
between the minor mating edge surface 37 and the major
arcuate edge surface 35 wherein a pair of laterally
extending ears or tabs 41 are located. As can be seen in
FIG. 8, the ears 41 are the same thickness as the flat
leaflets 15 from which they laterally extend. The ears
41 are elongated in an upstream-downstream direction when
viewed in their open orientation. FIGS. 7 and 9 show
that the ears 41 have lateral edge surfaces which are
rectilinear surfaces of generally shallow curvature as
viewed looking at the leaflet from the inflow surface 31.
More specifically, as best seen in FIG. 7, they each have -
a shallow rounded upstream edge surface 43 and a
generally similar downstream edge surface 45. The
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upstream edge surface 43 is the longer, extending
generally laterally of the ear, and it meets and blends
smoothly into the downstream surface 45. The major
' portion of the rectilinear upstream edge surface 43 is
perpendicular to the flat inflow and outflow surfaces of
- the leaflets 15, which flat surfaces simply extend
through the regions of the ears, so that the ears have
inflow and outflow surfaces that are coplanar with the
leaflet main body inflow and outflow surfaces 31, 33. A
short arcuate transition edge section 47 is interposed
between the major arcuate edge surface 35 and the flat
section 39.
As previously mentioned, the valve body 13 is formed
with the thickened wall sections 21 in the regions where
the cavities 25 are located, and preferably these
thickened sections are formed with flaring transition
surfaces, i.e. an upstream transition surface 49 and a
downstream transition surface 51 which lead smoothly from
the circular entrance region and the circular exit region
of the valve body to the flat wall surfaces 23 wherein
the cavities 25 are located. A surface such as the
surface 49 may be referred to as a radial swept surface.
As a result, the flow passageway through the valve body
is generally circular in cross-section except for the two
thickened sections 21 which extend inward to the flat
wall surfaces 23. As previously indicated, the plane
containing the centerline axis of the generally circular
passageway that is oriented perpendicular to the flat
surfaces 23 is referred to as the centerline plane and is
frequently used for reference purposes throughout this
specification.
The arrangement is such that each thickened section
includes two side-by-side cavities which are mirror
images of each other and which are located on opposite
sides of this centerline plane. As seen in FIGS. 12 and
13, the cavities 25 each have a curved sidewall region 53
surrounding a central flat rear section 54~ however, the
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depth of the cavities 25 is such that the apex of the
curved upstream edge surface 43 of the ear does not quite
touch the rear walls 54 of the cavities, e.g. a clearance
of about 1-4 mils (0.001-0.004 inch). The flat wall
surfaces 23 of the thickened regions serve as the primary
bearing surfaces against which one or the other of the
straight edge surfaces 39 of the leaflets will usually
bear whenever the leaflet is moving between its open and
the closed positions. The clearance between the shallow
curved edge surface 43 of the ear and the rear wall of
the cavity is such to facilitate a controlled cleansing
spurt of blood flow, upstream through the cavity past the
leaflet ears during the moment of complete closure of the
valve as shown in FIG. 4; this guards against the
possibility of the occurrence of clotting in the pivot
region. The proportioning of the ears 41 and the
cavities is such that this cleaning leak is not a high
velocity jet that might cause hemolysis; instead, it is a
controlled flow through a long narrow leak path that does
not induce thrombosis.
As best seen perhaps in FIG. 10, the cavities 25 are
formed to have an upstream lobe 57 and a downstream lobe
59 on opposite sides of an intermediate throat section
61. The intermediate throat section is formed by a pair
of curved fulcrums termed an outward fulcrum 63 and an
inward fulcrum 65 with respect to their location having
reference to the centerline plane. The outward fulcrum
63 is located substantially even with, but preferably
slightly upstream of said inward fulcrum.
3o The upstream lobe 57 is formed with an inclined,
straight, caroming wall section 67, which is oriented at
an angle of between about 5° and about 30° to the
centerline plane and preferably between about 15° and
about 25°. Although the caroming wall section 67 is part
of the peripheral wall region 53 and thus has curvature -
in a radial direction, it is substantially rectilinear
and is thus referred to as being straight. At its
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upstream end, the caroming wall section joins a concavely
curved wall section 69, which leads gradually downstream
from this junction point and serves a guidance function
that is described hereinafter.
The downstream lobe 59 includes a flat locator wall
' section 71 immediately below the inward fulcrum, at the
downstream end of which wall there is a downstream
sloping section 73 leading from its junction point to the
downstream end 75 of the cavity. The flat wall section
71 is oriented parallel to the centerline plane and thus
provides a guide surface against which the outflow
surfaces of the ears 41 bear in the full open position,
as best seen in FIGS. 2 and 9. As best seen in FIG. 8,
the leaflet ears 41 preferably have their rounded
downstream edge surfaces 45 oriented so as to be at an
acute angle to the outflow surface 33 of the leaflet,
thus presenting essentially a line of contact between the
tar d_oca_n_~t_rPa_m gdgP cpr farA a~ a»~ thg g~~p~~gw~ll
section 73, which tends to reduce friction and promote
cleansing in this region.
The leaflets 15 are installed in the valve body 13
by squeezing the body at diametrically opposite
locations, as for example along a diameter which is
perpendicular to the centerline plane. Such deformation
of the heart valve body 13 can take place in accordance
with the teachings of U.S. Patent No. 5,336,259, issued
August 9, 1994, the disclosure of which is incorporated
herein by reference. Squeezing causes the diametrically
opposed flat wall sections 23 to separate farther from
each other to permit the leaflets to be fitted into the
valve body, with the ears 41 being received in the
cavities 25. When the squeezing force is removed, the
valve body 13 returns to its original annular
configuration, leaving only the desired minimal clearance
_ 35 between the flat wall surfaces 23 of the valve body and
the straight lateral edge surfaces 39 of the leaflets, in
which positions the leaflets are slidably-pivotally
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mounted for travel between the open and closed positions.
The metal stabilizing ring 30 can be appropriately
installed, as by snapping into place or by shrink-
fitting, in the exterior circumferential groove 29
following the installation of the leaflets; however, it
may be preferred to install the metal stabilizing ring
before installing the leaflets. Pyrocarbon is the
preferred material of valve body construction, and
compressive force applied to a pyrocarbon structure by
such a metal ring can improve the structural properties
of a pyrocarbon valve body. Such a metal ring will be
chosen which will have sufficient resiliency to return to
its perfectly annular shape following removal of such a
squeezing force.
By designing the thickened bands 29a so that an
inclined ramp is formed at the downstream edge of the
downstream one of the two bands, it is possible to
install the metal ring 30 by sliding it upward from the
downstream end of the valve body 13 and allowing the
fingers 30a to snap into place; however, it should be
understood that the ring could be installed by shrink-
fitting if desired.
The irregular ring 30 is shaped so that a section
having an inwardly arcuate cross section is received in
the arcuate cross section groove and the adjacent section
having an inwardly cylindrical surface is seated snugly
upon one of the two raised bands 29a that flank the
groove 29, depending upon whether a mitral or an aortic
sewing ring is to be installed. The unique stiffening
ring 30 is designed to facilitate the installation of
either an aortic sewing ring or a mitral sewing ring
exterior of the valve body 13, as best seen by comparing
FIGS. 2 and 2A. In FIG. 2, an aortic sewing ring 81 is _
illustrated which is designed to leave the upstream
exterior surface of the valve body free and clear to _
permit its insertion into the aortic annulus from which
the defective natural. valve was excised. For this
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installation, the irregular stiffening ring 30 is slid
onto the valve body 13 from the downstream end with the
smaller section having the arcuate, radially inward
projections leading. Each of the projections are
connected by a thin neck section to the main portion of
the stiffening ring as best seen in FIGS. 3 and 3A, which
has a cylindrical radially interior face. When the
leading projections reach the downstream band 29a
flanking the groove 29, sufficient deflection occurs for
the ring to continue its upstream travel until the groove.
is reached, into which the projections then snap in
place, as seen in FIG. 6, with the main portion of the
stiffening ring tightly surrounding the downstream
cylindrical band 29a of the valve body and preferably
placing it in at least slight compression.
When the valve body is to be equipped with a mitral
sewing ring 83 as depicted in FIG. 2A, such sewing ring
is positioned so as to occupy a major portion of the
exterior wall surface of the valve body 13 upstream of
the groove 29, leaving the downstream section free for
insertion into the tissue annulus from which the
defective natural valve was excised. For this sewing
ring, the stiffening ring 30 is installed with the
opposite orientation, being slid upward from the
downstream end of the valve body 13 with the larger
section of the ring 3o having the cylindrical radially
interior surface leading. When it reaches the downstream
band 29a, it can be forced upstream therepast, and the
arcuate inward-facing surfaces of the projections again
slide over the downstream band 29a as a result of the
combined deflection which occurs. The projections again
snap in place in the groove 29, but in this instance the
major section of the ring 30 is seated tightly about the
upstream band 29a, as shown in FIGS. 2A and 13.
_ 35 The depth of the shallow groove 29 is such that the
thickness TZ (FIG. 14) at the location of the groove is
equal to at least about 85% of the thickness T~ of the
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major cylindrical section of the valve body. The
thickness T3 at the location of the bands 29a need not be
greater than about 120% of the thickness T~. This
strategic spacing and proportioning in a valve body 13 of
the present design allows the wall thickness of the major
portion of the valve body to be minimized, thus allowing
a larger diameter opening for the passageway through the
valve body. Generally, it is now felt that this interior
diameter of the valve should be as large as tolerable
(while still providing adequate structural strength)
because the pressure loss through the valve increases
relative to the fourth power of the diameter. Of course,
each heart valve excised from the heart of a particular
patient will vary with each patient, and therefore a
surgeon should have available a set of prosthetic valves
of different sizes generally ranging in exterior diameter
from about 19 millimeters to 33 millimeters in diameter
for fully grown adults. The reference measurement is
that of the tissue annulus remaining after the defective
natural valve has been excised.
The present valve design is such that it can be
effectively installed so that the tissue annulus is in
direct contact with the outer surface of the valve body
13 for valves that are installed both in the aortic
position and in the mitral position. In this respect, it
should be understood that, when installed, the raw edge
of the tissue annulus will be in contact with the
exterior surface of the valve body in the regions marked
"A" in FIGS. 2 and 2A. One result of this arrangement is
evident from FIG. 2A where it can be seen that the
diameter of the substantially circular passageway through
the valve is a very large percentage of the diameter of
the tissue annulus, which is made possible because of the
relative thinness of the major portion of the valve body
wall, particularly in the region of the tissue annulus.
Alternatively, as indicated above the ring can be
heated and shrink-fit onto the valve body so that the
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main body of the ring 30 is in contact with the desired
band 29a. Such shrink-fitting allows greater compressive
force to be applied to a pyrocarbon structure by such a
metal ring and can improve the structural properties of
the pyrocarbon which, as indicated above, is the
preferred material of construction. Of course, if the
ring is to be installed prior to the installation of the
leaflets, a metal is chosen which has sufficient
resiliency to return to its perfectly annular shape
following removal of the squeezing force.
With the heart valve operatively installed in a
patient, when it is in the open position, the two
leaflets 15 assume an open equilibrium position with
respect to the high flow and the direction of blood
downstream through the passageway, which may be an
orientation where they are substantially parallel to the
centerline plane, as illustrated in FIGS. 2 and 2A. The
location of the ear 41 within the cavity is illustrated
in FIG. 10, from which it should be apparent that, should
the dynamic blood forces within the valve body passageway
change, the left-hand leaflet which is shown can rotate
slightly clockwise so as to maintain such a low energy
position either with or without some slight translation.
In such an equilibrium position, the leaflets 15 provide
very low obstruction to the downstream flow of blood.
Yet, despite even such a substantially parallel, full
open position, the pivot construction is such that any
translational movement either downstream or upstream from
this substantially parallel position causes the leaflets
to rotate in the direction of,closing. Furthermore, in
the fully open position as shown in FIG. 2, the leaflets
15 are mounted so as to divide the valve body passageway
into 3 sections, a center section located between the two
leaflets 15 and two flanking sections. As best seen in
_ 35 FIG. 5, the arrangement is such that the cross-sectional
area of each of the two flanking passageway sections is
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preferably at least as large as the cross-sectional area
of the center flow passageway section.
As previously indicated, the combination of this
particular support of the leaflets 15, together with the
shape and proportioning of the valve body l3.contributes
to the achievement of smooth nonturbulent flow and the
absence of stasis. The toroidal curvature of the curved
entrance end 19 leading to a generally cylindrical valve
body of substantial overall axial length has been found
to achieve this desired end. More specifically, the
construction of a valve body to have a curved entrance
transition to a tabulated cylindrical, elongated
passageway has been found to provide very low pressure
drop for a passageway of a particular diameter, which is
substantially lower than present commercial mechanical
heart valves of the same size. The average axial length
of the valve is preferably at least 50% of the interior
diameter thereof. The entrance section should constitute
not more than about one-third of the average axial length
of the valve body, and it should smoothly join with the
downstream section, preferably being tangent thereto.
The entrance section is preferably essentially a section
of the surface of a torus. The torus is selected so that
the interior diameter of the torus is between 80% and
120% of the diameter of the interior circular cross-
section of the passageway through the valve body, and
preferably between about 90% and 100%. Most preferably
it is about 100% so that it will be substantially tangent
to the right circular cylindrical downstream interior
surface; if not, a short transition section is included.
Because the thickness of the valve body is uniform, the
exterior surface is a concave toroidal section.
The radius of curvature of the circle that is
revolved to create the torus is between about 28% and
about 80% of the radius of the valve body and preferably
between about 40% and about 650. In FIG. 14, the
interior radius of the valve body is marked "R~", and the
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radius of curvature of the torus is marked "R2". To
facilitate aortic installation, the exterior diameter DE
at the entrance end 19 should not be more than about 10%
greater than the exterior diameter D~ of the major
cylindrical outer surface; it should be at least about 6%
greater, preferably, about 6-7%. By locating the
stiffening ring at a location along the valve body that
is downstream of the leaflet pivot axes, i.e. downstream
of the fulcrums where the contact for pivoting is
1o defined, it can accommodate suture rings designed to have
the~raw edge of the tissue annulus directly lie in
contact with the exterior surface of the valve body
either upstream or downstream of such suture ring in the
regions A in FIGS. 2 and 2A. Such an arrangement
contributes to a thinner wall thickness and a larger
interior diameter for the passageway.
During conditions of high rate of flow of blood
downstream through the valve body, both leaflets 15 can
be oriented substantially parallel to the centerline of
the valve with the outflow surfaces of the ears 41 in
contact with the flat wall sections 71 of the downstream
lobes of the cavities 25 and with the ear upstream edge
in juxtaposition with the camming wall 67 so that
rotation past the parallel orientation is prohibited.
The flow rate of blood through the valve during the
pumping stroke of the associated chamber of the heart
will generally exert sufficient force upon the inflow
surfaces 31 of the leaflets such as to maintain the
leaflets in this substantially parallel alignment.
However, when the peak downstream flow of blood has
passed so that it slows in its approach to zero flow,
prior to the beginning of the reverse flow cycle, the
forces of the flowing bloodstream tending to orient the
leaflets in such a parallel position lessen, and as a
result, the drag of the bloodstream against all of the
surfaces of the leaflet becomes the predominant force.
This net force tends.to move the leaflets and the ears 41
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slightly farther downstream, which is permitted by the
contour of the downstream lobes 59. However, such
further downstream leaflet movement is guided by the
engagement of the outflow surface edges of the downstream
ear surfaces 45 along the sloping sections 73 of the
cavity and the inward fulcrums 65. The result of the
ears 41 shifting to such downstream positions, as shown
in FIG. 10A, is that the leaflets are no longer parallel
to the centerline; instead, they have rotated slightly
toward the closed orientation, i.e. so that they are now
preferably at an angle to the centerline of about 2° to
about 5°, and preferably 3° or greater, as depicted in
FIG. 3. This prerotation of the leaflets 15 occurs near
the end of pumping stroke and reduces the amount of
regurgitation, i.e. the volume of blood which will pass
upstream through such prosthetic heart valve prior to the
occluders next reaching their fully closed position
orientations, on the next closing. This reduction occurs
for the following two reasons: (a) the leaflets now need
to pivot a fewer number of angular degrees to reach the
closed position by reason of the headstart they have from
the substantially parallel orientation and (b) the
backflowing blood has the immediate opportunity to
preferentially contact the leaflet outflow surfaces 33,
as opposed to the inflow surfaces 31, so that this
component of the overall forces being applied to the
leaflets during closing is increased.
More specifically, as the reverse flow of blood
upstream through the valve begins, the leaflets 15 and
the ears 41 immediately translate upstream. This
upstream translation of the ears causes immediate caroming
engagement of the inflow surface edge of each upstream
edge surface 43 against the adjacent straight caroming -
wall section 67 of each cavity, while the outflow
surfaces of the ears may slide along the rounded inward .
fulcrums 65. By caroming engagement is meant contact
wherein there is relative sliding movement along a
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surface which is inclined to the direction in which the
net forces are attempting to move an object, i.e.
upstream and parallel to the centerline of the valve
body; this caroming action causes the leaflet to very
promptly pivot or swing toward its closed position while
the translation movement continues. Accordingly,
upstream translational movement of the ear in the cavity
25 assures that the pivoting of each leaflet toward its
closed position orientation occurs promptly at the very
l0 beginning of reverse flow and continues, driven by these
forces, until the upstream edges of the leaflet ears
reach the top of the upstream lobes 57, as illustrated in
FIG. 10B. Such initial pivoting is guided by the
movement of the inflow surface edge of the ear upstream
surface 43 along the caroming surface 67 while the outflow
ear surface generally slides along the inward fulcrum 65,
causing such pivoting or rotation to take place about a
center of rotation of pivot that is remote, i.e. which is
located substantially past the centerline plane of the
valve body; as a result, the length of the moment arm
acts to accelerate the initial rotational closing
movement. Very low friction is encountered because there
is no engagement between the ears and the walls of the
cavities such as would create a significant frictional
force that would resist closing.
When the force of the backflowing blood against the
outflow surface 33 of each leaflet has become
significant, it causes the inflow surfaces of the ears to
contact the outward fulcrums 63, as shown in FIG. 10C,
and pivoting thereafter continues guided in part by
sliding contact with the outward fulcrum 63. The leaflet
has thus pivoted a significant amount as a result'of the
- upstream translation and the shifting to contact with the
outward fulcrum 63. Thereafter, the upstream edge
surfaces of the ears are guided by movement along the
arcuate wall section 69 while the ears simultaneously
engage the outward fulcrums 63. Contact with the concave
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wall sections 69 and the fulcrums 63 remains
substantially continuous for about the final one-half of
the angular rotation of the ears, and the curvature of
the wall 69 is designed so that substantially only
rotational motion occurs as the upstream edge surfaces 43
slide therealong as the leaflets thereafter swing to the
fully-closed position, illustrated in FIG. 10D and in
FIG. 4. In such position, mating edge surfaces 37 of the
leaflets abut each other, and the downstream arcuate edge
surfaces 35 of the leaflets abut and seat against the
cylindrical interior surface 17 of the valve body.
During a major portion of the closing movement and
specifically during the final stages, this motion is
almost pure rotational motion to avoid sliding of the
ears along the fulcrums at this time when the upstream
edges of the ears move slightly downstream as a result of
this rotation. When the mating edges 37 of the two
leaflets meet, the contact between the upstream edge of
each ear and the arcuate wall 69 is broken, as seen in
FIG. 10D, thus avoiding. the possibility of localized wear
when the pressure across the valve is very high. When
the leaflet reaches its nearly closed position, the
liquid between the edge 35 of the leaflet and the orifice
wall acts like a cushion, and the leaflet further
decelerates just before it impacts the wall, reducing the
noise and any propensity for cavitation.
In the fully closed valve with the leaflets 15
oriented as illustrated in FIG. 4 wherein they are shown
in elevation, the force of the blood against the outflow
surface 33 of each leaflet is borne mainly by the
downstream arcuate edge surfaces 35 seating against the
interior valve body surface and by the ears 41 bearing
against the outward fulcrums 63. At the instant complete
closure is achieved, the pressure of the blood against
the outflow surfaces of the leaflets is at its highest -
and results in controlled leakage through the cavities 25
in an upstream direction. Such leakage is around and
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past the ears 41 in each cavity as can be seen from FIG.
10D and is controlled in part by the depth and the length
of the ears 41. The dimensioning of the ears and the
cavities creates a pathway for controlled backflow
laterally past the edges of the leaflet ears and thus
' tends to concentrate such leakage backflow in the regions
of the pivot arrangements where such cleansing flow
serves to positively guard against the occurrence of
clotting. In this respect, the average clearance between
the edges of the ears 41 and the walls of the cavities 25
is preferably at least about 50 microns or about 0.002
inch, with the clearance being the least at the region of
the apex of the curved upstream edge surface 43. There
may be slightly greater clearance adjacent the edge
surfaces 45 (FIG. 7) of the ears because of the
translating design of the leaflets.
When blood flow again reverses, as for example when
the pumping stroke of the associated chamber begins
again, downstream displacement, i.e. translation, of the
leaflets 15 initially occurs as a result of the force of
the blood against the inflow surfaces 31. As is evident
from FIG. 10D, the outflow surfaces of the ears 41 will
quickly come in contact with the inward fulcrums 65,
causing opening pivoting motion to quickly begin with the
major arcuate edge surface 35 swinging downstream. The
downstream edge surfaces 45 of the ears will likely reach
the lower arcuate ends 75 of the downstream lobes 59
prior to the ears rotating completely about their pivot
points on the fulcrums 65; however, when the blood flow
through the valve approaches maximum, the net forces on
the inflow surfaces 31 of the leaflets are such that the
ears will be ramped upstream along the sloping wall
- sections 73, causing the leaflets to be displaced just
slightly upstream until the substantially parallel
_ 35 position shown in FIG. 10 is reached, with the ears
abutting the flat wall section 71 in each downstream lobe.
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Illustrated in FIGS. 16, 17 and 18A-18D is an
alternative embodiment of a prosthetic heart valve 111
which is constructed so as to facilitate the leaflets
aligning parallel to the valve centerline or at slight
deviations thereto depending upon instantaneous
variations in the blood flow path, whichever is the low
energy orientation. The cavities are particularly shaped
so that the leaflet ears can reach such a parallel
orientation initially and can move slightly away from and
return to such an orientation during blood flow through
the valve for a single pumping stroke. The heart valve
111 includes a generally annular valve body 113 which is
generally similar to that previously described. It is
designed to function with a pair of leaflets that are
exactly the same as those previously described. Thus,
the reference numerals 15 are used, and the description
of the leaflets is not repeated. The valve body 113 has
an interior wall surface which includes two arcuate
sections 117 that respectively flank two diametrically
opposed flat wall sections 123, and it is likewise formed
with the smoothly curved entrance region 119 at its
upstream end. A pair of cavities 125 is formed in each
flat wall section 123, and shallow notches 127 formed in
the downstream wall portion of the valve body provide
side openings into the passageways and create a scalloped
profile for the valve body 113.
The generally right circular cylindrical surface of
the major portion of the exterior of the valve body 113
is interrupted by a thickened band 129 which facilitates
the installation of a suture ring 130. In the embodiment
illustrated in FIG. 16, a suture ring 130 is
schematically depicted of a type that would be used to
mount the heart valve 111 in the aortic position. When -
the valve 111 is so mounted, the raw tissue annulus
remaining where the defective valve was excised lies in
direct contact with the exterior surface of the valve
body in the region marked A in FIG. 16 which constitutes
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a concave surface section of the interior of a torus. It
can be seen that this arrangement maximizes the opening
of the valve passageway relative to the patient's tissue
annulus, promoting high flow rate of blood with very low
pressure drop thereacross, oftentimes lower than a
commercial mechanical valve which is two sizes larger.
Moreover, the outward surface curvature directs tissue
regrowth or panus outward away from the entrance of the
aortic valve.
The valve body 113 fairly closely resembles that
hereinbefore described; it has a pair of thickened wall
sections wherein the cavities 125 are located that are
formed with flaring transition surfaces, i.e. an upstream
transition surface 149 and a downstream transition
surface 151. Each thickened section includes two side-
by-side cavities 125 which are mirror images of each
other and which are located on opposite sides of the
centerline plane perpendicular to the flat wall sections
123. The cavities are best seen in FIGS. 18A through 18D
wherein the details of curvature are shown in each. right-
hand cavity, and omitted from each left-hand cavity so as
not to detract from the description of the movement of
the leaflet ears 41 within the cavities. As best seen
perhaps in FIG. 17, each of the cavities 125 has a curved
sidewall region 153 which is peripheral to a central flat
rear section 155. The cavities are each formed with an
upstream lobe 157 and a downstream lobe 159 located on
opposite sides of an intermediate throat section 161,
which is formed by a curved outward fulcrum 163 and a
curved inward fulcrum 165.
The upstream lobe 157 is formed with an inclined,
straight, camming wall section 167 which is oriented at
. an angle of between about 5° and about 30° to the
centerline plane, and preferably between about 15° and
about 25° thereto. At its upstream end, the caroming wall
section 167 joins a concavely curved wall section 169
which leads gradually downstream from this junction point
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and serves to guide the final swinging movement of the
leaflets to the closed position.
The downstream lobe 159 includes a flat locator wall
section 171 which is located immediately below the inward
fulcrum 165. A flat bottom wall 173 extends at right
angles from the downstream end of the locator wall 171 in
a direction outward and away from the centerline plane of
the valve body. The flat wall section 171 is oriented
parallel to the centerline plane and provides a guide
surface against which the outflow surfaces of the leaflet
ears 41 abut in the full open position, as best seen in
FIGS. 16 and 18A. In this position as can be seen from
FIG. 18A, the downstream edge 45 of the leaflet ear abuts
the flat bottom wall 173 of the cavity.
The leaflets 15 are installed in the valve body 113
and the suture ring 13o thereupon as generally
hereinbefore described. With the heart valve 111
operatively installed for example as a replacement aortic
valve in a patient, when the ventricle with which it is
associated is pumping,. it will be in the open position
with the two leaflets 15 assuming an equilibrium open
position with respect to the high flow of blood
downstream through the passageway, as shown in FIG. 16.
As soon as reverse flow of blood upstream through
the valve begins, the leaflets 15 immediately translate
upstream causing the upstream edges 43 of the ears to
slide along the caroming wall sections 167, as previously
described with respect to the valve 11. This causes each
leaflet to very promptly begin to swing toward its closed
position as the upstream translation proceeds. Once the
ears 41 reach the top of the upper lobes 157, as
illustrated in FIG. 18B, the leaflets will have swung
away from the parallel orientation and have become -
significantly cocked or canted to the direction of
downstream blood flow, so that the force of the
backflowing blood against the outflow surface of each
leaflet causes the ears to shift away from the inward
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fulcrums 163 and abut the outward fulcrums 163 as
depicted in FIG. 18C. Thereafter, the upstream edge
surfaces of the ears 41 are guided by movement along the
arcuate wall section 169 while the inflow surfaces of the
ears remain in contact with the outward fulcrums 163 as
shown in FIG. 18C. Contact of the ears 41 with the
concave wall sections 169 and with the outward fulcrums
163 remains substantially continuous throughout about the
final one-half of the angular closing movement, and the
curvature of the wall 169 is designed so that
substantially only rotational movement of the ears occurs
as the upstream edge surfaces 43 slide therealong during
the completion of the leaflets swinging to the fully-
closed position illustrated in FIG. 18D. In such
position, the mating edge surfaces 37 of the leaflets
abut each other, and the downstream arcuate edge surfaces
35 of the leaflets are seated against the cylindrical
interior surface 117 of the valve body 113, as previously
described with respect to the closing movement in the
heart valve 11.
When downstream blood flow again begins with the
next pumping stroke of the associated ventricle,
downstream translation of the leaflets 15 initially
occurs as a result of the force of the blood against the
inflow surfaces 31. As will be evident from FIG. 18D,
the outflow surfaces of the ears 41 will quickly contact
the inward fulcrums 165, causing opening pivoting motion
to quickly begin, with the major arcuate edge surfaces 35
swinging downstream with some translation as the ears
also slide along the inward fulcrums 165. As a result of
this translation, the downstream edge surfaces 45 of the
ears will likely reach the bottom flat walls 173 of the
- downstream lobes prior to the ears rotating completely
about their pivot points on the fulcrums 165; however,
- 35 the flat bottom wall surfaces 173 allow the downstream
edges to easily slide therealong and move smoothly and
quickly to the full open position, where the outflow
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surfaces of the ears are in abutting contact with the
locator surfaces 171. If instantaneous blood flow
thereafter is such that a substantially parallel
orientation is not the low energy position, either or
both of the leaflets can easily shift slightly because
the upstream portions of the tabs are relatively loosely
constrained within the throat of the cavities between the
facing fulcrums and the downstream edge is free to slide
along the bottom flat wall 173. However, once such an
instantaneous condition ends and straight downstream flow
again occurs, because of the flat transverse downstream
bottom surface, a leaflet that was momentarily displaced
can quickly return to the low energy parallel position as
the downstream edge 45 of the ear slides along the flat
perpendicular bottom surface 173.
By confining substantially all of the functionally
engaging surfaces that define the paths of opening and
closing movement of the leaflets to the regions of the
cavities and the ears, many of the regions where it is
necessary to hold very close tolerance are concentrated,
thereby facilitating both manufacturing processes and
quality-control fitting-up procedures. These
advantageous results are felt to grow out of the
illustrated upstream-downstream lobe design where the
lobes are separated by a narrow throat that is formed by
the flanking fulcrums which confine the associated
leaflet ear and assure smooth movement and positive
resistance to jamming. Such a design can effectively
function by the use of ears which have cross sections
that are generally elongated rectangles or trapezoids,
i.e. quadrilaterals having 2 parallel walls of a length
at least about 3 times its thickness, in such double-
lobed cavities. Moreover, by limiting at least the final -
about one-third of the closing movement of the leaflets
to one of substantially rotation only, the likelihood of
severe wear occurring at such points of contact, when
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force on the leaflet ears is at about its maximum, is
greatly diminished.
The overall design of the valve is such that gross
hemodynamics in terms of energy loss per cardiac cycle
are completely acceptable and are superior to mechanical
' ~ heart valves that are presently commercially available,
often exhibiting a pressure drop lower than that of the
next larger size and sometimes equal to that of such a
valve 2 sizes larger. Because blood is a very delicate
tissue and even minor abuses caused by turbulence and
high shear can result in thrombosis or emboli generation
at local regions of stagnation, it is very important that
excessive turbulence coupled with high shear stresses and
local regions of stasis be avoided. The foregoing valve
design has been found to excellently fulfill such
requirements. The employment of leaflets with
rectilinear surfaces that are free to follow and easily
orient themselves substantially parallel to straight
downstream blood flow minimizes the turbulence associated
with the leaflets themselves. A desired cavity design
which can effect prerotation of the leaflets after the
downstream flow through the valve has peaked and nears
the end of its cycle can often further reduce
regurgitation; however, the pivot arrangement itself and
the location of the side notches 27 in the valve body
that focus the inflowing blood against the outflow
surfaces 33 where the initial closing rotation forces are
amplified are significantly instrumental in achieving
this desired end result.
Although the invention has been described with
respect to certain preferred embodiments, which include
what the inventors presently consider to be the best mode
for carrying out the invention, it should be understood
that various changes and modifications that would be
obvious to one having the ordinary skill in this art may
be made without departing from the scope of the invention
which is defined by the claims appended hereto. For
CA 02218621 1997-10-17
WO 96/36299 PCT/US96/06466
-32-
example, as earlier indicated, the invention is not
limited to occluders in the form of leaflets having flat
body sections but is considered to be also applicable to
leaflets having curved body sections with substantially
rectilinear surfaces. In this respect, it may be
desirable to facilitate the creation of a central
passageway of greater area through such a bileaflet valve
by employing a pair of such curved leaflets to achieve a
different distribution of the downstream blood flow
through the valve body.
