U.S. patent application number 11/745260 was filed with the patent office on 2007-09-06 for septum attached ventricular support.
This patent application is currently assigned to Acorn Cardiovascular, Inc.. Invention is credited to Clifton Alferness, Michael Girard, Donald Palme, Donald Rohrbaugh, James Edward Shapland.
Application Number | 20070208211 11/745260 |
Document ID | / |
Family ID | 24571112 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070208211 |
Kind Code |
A1 |
Shapland; James Edward ; et
al. |
September 6, 2007 |
SEPTUM ATTACHED VENTRICULAR SUPPORT
Abstract
A method and device are disclosed for treating congestive heart
disease. The material of the device is secured to the heart
proximate the septal wall. The material covering the ventricles may
or may not have the same tension and or compliance. The device can
be constructed as a unitary "jacket" that is slipped over the apex
of the heart. Alternately, the device implanted as one, two or more
separate components. In one embodiment, the material covers both
the left and right ventricles. In another embodiment, the material
covers only one ventricle. The device may include at least one
adjustment mechanism configured to adjust the tension of the
material. Preferably, the device includes a first adjustment
mechanism configured to adjust a tension of the material covering
the right ventricle and a second adjustment mechanism configured to
adjust the tension of the material covering the left ventricle such
that the tension of the material covering the left ventricle can be
different than the tension of the material covering the right
ventricle.
Inventors: |
Shapland; James Edward;
(Vadnais Heights, MN) ; Alferness; Clifton;
(Redmond, WA) ; Palme; Donald; (Princeton, MN)
; Girard; Michael; (Lino Lakes, MN) ; Rohrbaugh;
Donald; (Minnetonka, MN) |
Correspondence
Address: |
FAEGRE & BENSON LLP;PATENT DOCKETING
2200 WELLS FARGO CENTER
90 SOUTH SEVENTH STREET
MINNEAPOLIS
MN
55402-3901
US
|
Assignee: |
Acorn Cardiovascular, Inc.
St. Paul
MN
55112
|
Family ID: |
24571112 |
Appl. No.: |
11/745260 |
Filed: |
May 7, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11338571 |
Jan 24, 2006 |
7214181 |
|
|
11745260 |
May 7, 2007 |
|
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10453053 |
Jun 2, 2003 |
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11338571 |
Jan 24, 2006 |
|
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09641141 |
Aug 17, 2000 |
6572533 |
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10453053 |
Jun 2, 2003 |
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Current U.S.
Class: |
600/16 ; 606/1;
606/151; 606/213 |
Current CPC
Class: |
A61F 2/2481
20130101 |
Class at
Publication: |
600/016 ;
606/001; 606/151; 606/213 |
International
Class: |
A61B 17/00 20060101
A61B017/00 |
Claims
1. A device for treating cardiac disease of a heart having a
longitudinal axis from an apex to a base, an upper portion and a
lower portion divided by an A-V groove, a valvular annulus adjacent
said A-V groove, and ventricular lower extremities adjacent said
apex, said ventricular lower extremities comprising a right
ventricle and left ventricle wherein said right and left ventricle
are separated by a septum, the device comprising: a jacket of
flexible material having upper and lower ends dimensioned to cover
at least said left ventricle or at least said right ventricle; said
material adapted to be adjusted on said heart to snugly conform to
an external geometry of said heart and constrain circumferential
expansion of at least said left ventricle or at least said right
ventricle during diastole and permit substantially unimpeded
contraction of said heart during systole, wherein pressure exerted
by said device on said right ventricle during diastole is different
than pressure exerted by said device on said left ventricle during
diastole.
2. The device of claim 1, wherein said material is adapted to be
secured to said heart proximate said septum.
3. The device of claim 1, wherein said material is secured to said
heart by fibrosis.
4. The device of claim 1, wherein said device covers said left and
right ventricle.
5. The device of claim 4, wherein said device is constructed as a
unitary jacket.
6. The device of claim 4, wherein said device comprises a first
component comprising material configured to cover said left
ventricle and a second component comprising material configured to
cover said right ventricle, wherein said first and second
components are implanted separately.
7. The device of claim 4, wherein said material covering said right
ventricle has a greater compliance than said material covering said
left ventricle.
8. The device of claim 4, wherein said material covering said left
ventricle is under more tension than said material covering said
right ventricle.
9. The device of claim 1, further comprising at least one
adjustment mechanism configured to adjust a tension of said
material.
10. The device of claim 4, further comprising a first adjustment
mechanism configured to adjust a tension of said material covering
said right ventricle and a second adjustment mechanism configured
to adjust a tension of said material covering said left ventricle,
wherein the tension of the material covering said left ventricle is
greater than the tension of the material covering said right
ventricle.
11. The device of claim 7, wherein said adjustment mechanism
comprises material that is sufficiently flexible such that excess
amounts of said material can be gathered following placement of
said material over said heart to snugly conform said material to an
external geometry of said heart.
12. The device of claim 9, wherein said adjustment mechanism
comprises a slot comprising opposing lateral edges, wherein the
tension of said material is adjusted by adjusting a proximity of
said opposing lateral edges.
13. The device of claim 9, wherein said adjustment mechanism
comprises an inflatable member mounted between said material and
the heart.
14. The device of claim 1, further comprising a securing
member.
15. The device of claim 14, wherein said securing member comprises
an inelastic band configured to extend along said septum when said
device is in place.
16. The device of claim 14, wherein said securing member comprises
a plurality of rings configured to extend along said septum when
said device is in place.
17. A device according to claim 1 wherein said material is
dimensioned to have a longitudinal dimension between said upper and
lower ends sufficient for said jacket to constrain said valvular
annulus.
18. A device according to claim 1 wherein said material encloses
said apex.
19. A device according to claim 1 wherein said apex protrudes
beyond said material.
20. A device according to claim 1 wherein said jacket is sized to
at least partially cover and constrain said upper portion.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/338,571, filed Jan. 24, 2006, entitled
SEPTUM ATTACHED VENTRICULAR SUPPORT, which is a divisional of
application Ser. No. 10/453,053, filed Jun. 2, 2003, entitled
CARDIAC DISEASE TREATMENT AND DEVICE, now abandoned, which is a
continuation of application Ser. No. 09/641,141, filed Aug. 17,
2000, entitled CARDIAC DISEASE TREATMENT AND DEVICE, now U.S. Pat.
No. 6,572,533, which applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to a method and device for
treating congestive heart disease and related valvular dysfunction.
More particularly, the invention provides a cardiac support device
with sections having variable compliance.
[0004] 2. Description of the Prior Art
[0005] Congestive heart disease is a progressive and debilitating
illness. The disease is characterized by a progressive enlargement
of the heart.
[0006] As the heart enlarges, the heart is performing an increasing
amount of work in order to pump blood each heart beat. In time, the
heart becomes so enlarged the heart cannot adequately supply blood.
An afflicted patient is fatigued, unable to perform even simple
exerting tasks and experiences pain and discomfort. Further, as the
heart enlarges, the internal heart valves cannot adequately close.
This impairs the function of the valves and further reduces the
heart's ability to supply blood.
[0007] Causes of congestive heart disease are not fully known. In
certain instances, congestive heart disease may result from viral
infections. In such cases, the heart may enlarge to such an extent
that the adverse consequences of heart enlargement continue after
the viral infection has passed and the disease continues its
progressively debilitating course.
[0008] Patients suffering from congestive heart disease are
commonly grouped into four classes (i.e., Classes I, II, III and
IV). In the early stages (e.g., Classes I and II), drug therapy is
the commonly prescribed treatment. Drug therapy treats the symptoms
of the disease and may slow the progression of the disease.
Importantly, there is no cure for congestive heart disease, Even
with drug therapy, the disease will progress. Further, the drugs
may have adverse side effects.
[0009] Presently, the only permanent treatment for congestive heart
disease is heart transplant. Heart transplant procedures are very
risky, extremely invasive and expensive and only shortly extend a
patient's life. Furthermore, not enough hearts are available for
transplant to meet the needs of congestive heart disease patients
and many patient's do not qualify for heart transplant for failure
to meet any one of a number of qualifying criteria.
[0010] Substantial effort has been made to find alternative
treatments for congestive heart disease. Recently, a new surgical
procedure has been developed. Referred to as the Batista procedure,
the surgical technique includes dissecting and removing portions of
the heart in order to reduce heart volume. This is a radical new
and experimental procedure subject to substantial controversy.
Furthermore, the procedure is highly invasive, risky and expensive
and commonly includes other expensive procedures (such as a
concurrent heart valve replacement). Also, the treatment is limited
to Class IV patients and, accordingly, provides no hope to patients
facing ineffective drug treatment prior to Class IV. Finally, if
the procedure fails, emergency heart transplant is the only
available option.
[0011] Clearly, there is a need for alternative treatments
applicable to both early and later stages of the disease to either
stop the progressive nature of the disease or more drastically slow
the progressive nature of congestive heart disease. Unfortunately,
currently developed options are experimental, costly and
problematic.
[0012] Cardiomyoplasty is a recently developed treatment for
earlier stage congestive heart disease (e.g., as early as Class III
dilated cardiomyopathy). In this procedure, the latissimus dorsi
muscle (taken from the patient's shoulder) is wrapped around the
heart and chronically paced synchronously with ventricular systole.
Pacing of the muscle results in muscle contraction to assist the
contraction of the heart during systole.
[0013] While cardiomyoplasty has resulted in symptomatic
improvement, the nature of the improvement is not understood. For
example, one study has suggested the benefits of cardiomyoplasty
are derived less from active systolic assist than from remodeling,
perhaps because of an external elastic support. The study suggests
an elastic support (i.e., a non-stimulated muscle wrap or an
artificial elastic sock placed around the heart) could provide
similar benefits. Kass et al., Reverse Remodeling From
Cardiomyoplasty In Human Heart Failure: External Support Versus
Active Assist, 91 Circulation 2314-2318 (1995).
[0014] Even though cardiomyoplasty has demonstrated symptomatic
improvement, studies suggest the procedure only minimally improves
cardiac performance. The procedure is highly invasive requiring
harvesting a patient's muscle and an open chest approach (i.e.,
sternotomy) to access the heart. Furthermore, the procedure is
expensive--especially those using a paced muscle. Such procedures
require costly pacemakers. The cardiomyoplasty procedure is
complicated. For example, it is difficult to adequately wrap the
muscle around the heart with a satisfactory fit. Also, if adequate
blood flow is not maintained to the wrapped muscle, the muscle may
necrose. The muscle may stretch after wrapping reducing its
constraining benefits and is generally not susceptible to
post-operative adjustment. Finally, the muscle may fibrose and
adhere to the heart causing undesirable support on the contraction
of the heart during systole.
[0015] In addition to cardiomyoplasty, mechanical assist devices
have been developed as intermediate procedures for treating
congestive heart disease. Such devices include left ventricular
assist devices ("LVAD") and total artificial hearts ("TAH"). An
LVAD includes a mechanical pump for urging blood flow from the left
ventricle and into the aorta. An example of such is shown in U.S.
Pat. No. 4,995,857 to Arnold dated Feb. 26, 1991. LVAD surgeries
are still in U.S. clinical trials and not generally available. Such
surgeries are expensive. The devices are at risk of mechanical
failure and frequently require external power supplies. TAH
devices, such as the celebrated Jarvik heart, are used as temporary
measures while a patient awaits a donor heart for transplant.
[0016] Other attempts at cardiac assist devices are found in U.S.
Pat. No. 4,957,477 to Lundback dated Sep. 18, 1990, U.S. Pat. No.
5,131,905 to Grooters dated Jul. 21, 1992 and U.S. Pat. No.
5,256,132 to Snyders dated Oct. 26, 1993. Both of the Grooters and
Snyders patents teach cardiac assist devices which pump fluid into
chambers opposing the heart to assist systolic contractions of the
heart. The Lundback patent teaches a double-walled jacket
surrounding the heart. A fluid fills a chamber between the walls of
the jacket. The inner wall is positioned against the heart and is
pliable to move with the heart. Movement of the heart during
beating displaces fluid within the jacket chamber.
[0017] Commonly assigned U.S. Pat. No. 5,702,343 to Alferness dated
Dec. 30, 1997 teaches a jacket to constrain cardiac expansion
during diastole. The present invention pertains to improvements to
the invention disclosed in the '343 patent,
SUMMARY OF THE INVENTION
[0018] According to a preferred embodiment of the present
invention, a method and device are disclosed for treating
congestive heart disease and related cardiac complications such as
valvular disorders. The invention includes a device constructed
from biologically compatible material dimensioned to cover at least
one ventricle of the heart. The device is adapted to be secured to
the heart and is adjustable to snugly conform to an external
geometry of the heart and to constrain circumferential expansion of
the heart during diastole and to permit unimpeded contraction of
the heart during systole.
[0019] In particular, the invention provides a device constructed
such that material covering one ventricle can have a different a
compliance or tension than material covering the other ventricle.
In a preferred embodiment, the material of the device is secured to
the heart proximate the septal wall.
[0020] The device can be constructed as a unitary "jacket" that is
slipped over the apex of the heart (See, for example, U.S. Pat. No.
5,702,343 to Alferness, dated Dec. 30, 1997, the disclosure of
which is incorporated by reference herein). Alternately, the device
may be implanted as two or more separate components (pieces of
material). In one embodiment, the device covers both the left and
right ventricles. In another embodiment, the device covers only the
left ventricle or only the right ventricle.
[0021] Preferably, the device includes at least one adjustment
mechanism configured to adjust the tension of the material. More
preferably, the device includes a first adjustment mechanism
configured to adjust a tension of the material covering the right
ventricle and a second adjustment mechanism configured to adjust
the tension of the material covering the left ventricle such that
the tension of the material covering the left ventricle can be
different than the tension of the material covering the right
ventricle.
[0022] The invention also provides a method for implanting the
device, both as a unitary device, or as multiple components,
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic cross-sectional view of a normal,
healthy human heart shown during systole;
[0024] FIG. 1A is the view of FIG. 1 showing the heart during
diastole;
[0025] FIG. 1B is a view of a left ventricle of a healthy heart as
viewed from a septum and showing a mitral valve;
[0026] FIG. 2 is a schematic cross-sectional view of a diseased
human heart shown systole;
[0027] FIG. 2A is the view of FIG. 2 showing the heart during
diastole;
[0028] FIG. 2B is the view of FIG. 1B showing a diseased heart;
[0029] FIG. 3 is a perspective view of a first embodiment of a
cardiac support device according to the present invention;
[0030] FIG. 3A is a side elevation view of a diseased heart in
diastole with the device of FIG. 3 in place;
[0031] FIG. 4 is a perspective view of a second embodiment of a
cardiac support device according to the present invention;
[0032] FIG. 4A is a side elevation view of a diseased heart in
diastole with the device of FIG. 4 in place;
[0033] FIG. 5 is a cross-sectional view of a device of the present
invention overlying a myocardium and with the material of the
device gathered for a snug fit;
[0034] FIG. 6 is an enlarged view of a knit construction of the
device of the present invention in a rest state;
[0035] FIG. 7 is a schematic view of the material of FIG. 6;
[0036] FIG. 8 is a perspective view of an alternate embodiment of a
cardiac support device according to the present invention;
[0037] FIG. 8A is a side elevation view of a diseased heart in
diastole with the device of FIG. 8 in place;
[0038] FIG. 9 is a perspective view of another embodiment of a
cardiac support device according to the present invention;
[0039] FIG. 9A is a side elevation view of a diseased heart with an
alternate embodiment of a variable compliance device of FIG. 9 in
place.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0040] Healthy Human Heart
[0041] With initial reference to FIGS. 1 and 1A, a normal, healthy
human heart H' is schematically shown in cross-section and will now
be described in order to facilitate an understanding of the present
invention. In FIG. 1, the heart H' is shown during systole (i.e.,
high left ventricular pressure). In FIG. 1A, the heart H' is shown
during diastole (i.e., low left ventricular pressure).
[0042] The heart H' is a muscle having an outer wall or myocardium
MYO' and an internal wall or septum S'. The myocardium MYO' and
septum S' define four internal heart chambers including a right
atrium RA', a left atrium LA', a right ventricle RV' and a left
ventricle LV'. The plane in which the valves separating the atria
and ventricles lie is visible from the exterior of the heart H' and
is designated as the valvular annulus VA'. The heart H' has a
length measured along a longitudinal axis AA'-BB' from an upper end
or base B' to a lower end or apex A'.
[0043] The right and left atria RA', LA'reside in an upper portion
UP' of the heart H' adjacent the base B'. The right and left
ventricles RV', LV' reside in a lower portion LP' of the heart H'
adjacent the apex A'. The ventricles RV', LV' terminate at
ventricular lower extremities LE' adjacent the apex A' and spaced
therefrom by the thickness of the myocardium MYO'.
[0044] Due to the compound curves of the upper and lower portions
UP', LP', the upper and lower portions UP', LP' meet at a
circumferential groove commonly referred to as the A-V groove AVG'.
Extending away from the upper portion UP' are a plurality of major
blood vessels communicating with the chambers RA', RV', LA', LV'.
For ease of illustration, only the superior vena cava SVC' and a
left pulmonary vein LPV' are shown as being representative.
[0045] The heart H' contains valves to regulate blood flow between
the chambers RA', RV', LA', LV' and between the chambers and the
major vessels (e.g., the superior vena cava SVC' and a left
pulmonary vein LPV'). For ease of illustration, not all of such
valves are shown. Instead, only the tricuspid valve TV'between the
right atrium RA' and right ventricle RV'and the mitral valve MV'
between the left atrium LA' and left ventricle LV' are shown as
being representative.
[0046] The valves are secured, in part, to the myocardium MYO' in a
region of the lower portion LP' adjacent the A-V groove AVG' and
referred to as the valvular annulus VA'. The valves TV' and MV'
open and close through the beating cycle of the heart H.
[0047] The right and left atria RA' and LA' receive blood from the
venous system and the right and left ventricles RV' and LV' pump
blood into the arterial system. The right atrium and ventricle RA'
and RV' are separated from the left atrium and ventricle LA' and
LV' by a muscular wall, or septum S'.
[0048] Blood in which the oxygen content has become partially
depleted and the carbon dioxide content has increased as a result
of tissue metabolism returns to the right atrium RA'. This blood
then enters the right ventricle RV', which pumps it into the
pulmonary arteries. The pulmonary arteries branch to transport
blood to the lungs. The blood that returns to the left atrium LA'
by way of the pulmonary veins LPV' is therefore enriched in oxygen.
The path of blood from the heart (right ventricle RV') through the
lungs; and back to the heart (left atrium LA') is referred to as
pulmonary circulation.
[0049] Oxygen rich blood in the left atrium LA' enters the left
ventricle LV' and is pumped into the aorta. Arterial branches from
the aorta supply oxygen rich blood to all of the organ systems and
are thus part of the systemic circulation.
[0050] Arterial pressure is significantly higher in the systemic
circulation than in the pulmonary circulation. Therefore the left
ventricle LV' performs more work than the right ventricle RV'. As a
result, in healthy hearts, the left ventricle LV' wall is generally
about twice as thick as that of the right ventricle RV'.
[0051] The Cardiac Cycle
[0052] The events that occur from the beginning of one heartbeat to
the beginning of the next are referred to as the cardiac cycle.
Generally, the cardiac cycle includes a period of relaxation called
diastole, during which blood flows from the veins into the atria
and ventricles, followed by a period of contraction called systole.
FIGS. 1 and 1A show a normals healthy heart H' during systole and
diastole, respectively. During systole (FIG. 1), the myocardium
MYO' is contracting and the heart assumes a shape including a
generally conical lower portion LP'. During diastole (FIG. 1A), the
heart H' is expanding and the conical shape of the lower portion
LP' bulges radially outwardly (relative to axis AA'-BB').
[0053] The motion of the heart H' and the variation in the shape of
the heart H' during contraction and expansion is complex. The
amount of motion varies considerably throughout the heart H'. The
motion includes a component which is parallel to the axis AA'-BB'
(conveniently referred to as longitudinal expansion or
contraction). The motion also includes a component perpendicular to
the axis AA'-BB' (conveniently referred to as circumferential
expansion or contraction).
[0054] During the initial segment of diastole, blood flows from the
veins, directly through the atria and into the ventricles. During
the final segment of diastole, the atria contract, causing
additional filling of the ventricles. In a typical human heart, the
right atrial pressure rises to about 4 to about 6 mmHg during
atrial contraction. In contrast, the left atrial pressure rises to
about 7 to about 8 mmHg during atrial contraction.
[0055] Immediately after ventricular contraction begins, the
ventricular pressure abruptly rises, causing the A-V valves to
close. The ventricular pressure then builds up sufficiently to push
the semilunar (aortic and pulmonary) valves open against the
pressures in the aorta and pulmonary artery. The ventricular
pressures push the semilunar valves open when the left ventricular
pressure rises above diastolic aortic pressure, to between about 80
mmHg to 85 mmHg, (and the right ventricular pressure rises above
pulmonary artery diastolic pressure, to between about 8 mmHg and 10
mmHg). At the end of systole, ventricular relaxation begins
suddenly, allowing the intraventricular pressures to fall rapidly.
The elevated pressures in the distended large arteries immediately
push blood back toward the ventricles, which snaps the aortic and
pulmonary valves closed. The ventricular muscle continues to relax
and the intraventricular pressures fall rapidly back to their low
diastolic levels. Then the AV valves open to begin a new cycle.
[0056] Comparison of a Diseased Heart and a Healthy Heart
[0057] Having described a healthy heart H' during systole (FIG. 1)
and diastole (FIG. 1A), comparison can now be made with a heart
deformed by congestive heart disease. Such a heart H is shown in
systole in FIG. 2 and in diastole in FIG. 2A. All elements of
diseased heart H are labeled identically with similar elements of
healthy heart H' except only for the omission of the apostrophe in
order to distinguish diseased heart H from healthy heart H'.
[0058] Comparing FIGS. 1 and 2 (showing hearts H' and H during
systole), the lower portion LP of the diseased heart H has lost the
tapered conical shape of the lower portion LP' of the healthy heart
H'. Instead, the lower portion LP of the diseased heart H bulges
outwardly between the apex A and the A-V groove AVG. So deformed,
the diseased heart H during systole (FIG. 2) resembles the healthy
heart H' during diastole (FIG. 1A). During diastole (FIG. 2A), the
deformation is even more extreme.
[0059] As a diseased heart H enlarges from the representation of
FIGS. 1 and 1A to that of FIGS. 2 and 2A, the heart H becomes a
progressively inefficient pump. Therefore, the heart H requires
more energy to pump the same amount of blood. Continued progression
of the disease results in the heart H being unable to supply
adequate blood to the patient's body and the patient becomes
symptomatic.
[0060] For ease of illustration, the progression of congestive
heart disease has been illustrated and described with reference to
a progressive enlargement of the lower portion LP of the heart H.
While such enlargement of the lower portion LP is most common and
troublesome, enlargement of the upper portion UP may also
occur.
[0061] In addition to cardiac insufficiency, the enlargement of the
heart H can lead to valvular disorders. As the circumference of the
valvular annulus VA increases, the leaflets of the valves TV and MV
may spread apart. After a certain amount of enlargement, the
spreading may be so severe the leaflets cannot completely close (as
illustrated by the mitral valve MV in FIG. 2A). Incomplete closure
results in valvular regurgitation contributing to an additional
degradation in cardiac performance. While circumferential
enlargement of the valvular annulus VA may contribute to valvular
dysfunction as described, the separation of the valve leaflets is
most commonly attributed to deformation of the geometry of the
heart H. This is best described with reference to FIGS. 1B and
2B.
[0062] FIGS. 1B and 2B show a healthy and diseased heart,
respectively, left ventricle LV', LV during systole as viewed from
the septum (not shown in FIGS. 1B and 2B). In a healthy heart H',
the leaflets MVL' of the mitral valve MV' are urged closed by left
ventricular pressure. The papillary muscles PM', PM are connected
to the heart wall MYO', MYO, near the lower ventricular extremities
LE', LE. The papillary muscles PM', PM pull on the leaflets MVL',
MVL via connecting chordae tendineae CT', CT. Pull of the leaflets
by the papillary muscles functions to prevent valve leakage in the
normal heart by holding the valve leaflets in a closed position
during systole. In the significantly diseased heart H, the leaflets
of the mitral valve may not close sufficiently to prevent
regurgitation of blood from the ventricle LV to the atrium during
systole.
[0063] As shown in FIG. 1B, the geometry of the healthy heart H' is
such that the myocardium MYO', papillary muscles PM' and chordae
tendineae CT' cooperate to permit the mitral valve MV' to fully
close. However, when the myocardium MYO bulges outwardly in the
diseased heart H (FIG. 2B), the bulging results in displacement of
the papillary muscles PM. This displacement acts to pull the
leaflets MVL to a displaced position such that the mitral valve
cannot fully close.
[0064] Having described the characteristics and problems of
congestive heart disease, the treatment method and apparatus of the
present invention will now be described.
[0065] Cardiac Support Device
[0066] In general, the invention provides a cardiac support device
configured to cover at least the left or right ventricular
myocardium to constrain against enlargement of the ventricular wall
of the heart H without restricting contraction of the heart H
during systole.
[0067] As used herein, "cover" means that the device is in contact
with the cardiac surface and reduces expansion of the heart wall
during diastole by applying a constraining force on the surface of
the heart. A device that "covers" the lower extremities of the
heart may be constructed as a continuous material that can
substantially encircle the external surface of the lower
extremities of the heart. In an alternate embodiment, the device is
constructed as one or two or more separate components. In, one
embodiment, the device is constructed from at least one component
configured to substantially overly one ventricle of the heart
(e.g., extend from septal wall to septal wall). Alternately, the
device may be constructed from one or more components, each of
which overly only a segment or piece of a ventricle.
[0068] The device 10 is adjusted to a snug fit on the heart H
during diastole. Care is taken to avoid tightening the device 10
too much such that cardiac function is impaired. During diastole,
the ventricles fill with blood. If the device 10 is too tight, the
ventricles may not adequately expand. During the fitting of the
device 10, the surgeon can monitor ventricular pressure, for
example, by monitoring pulmonary wedge pressure. While minor
increases in pressure (e.g., 2-3 mmHg) can be tolerated, the device
10 is snugly fit on the heart H but not so tight as to cause a
significant increase in left ventricular pressure during
diastole.
[0069] With reference now to FIGS. 3, 3A, 4 and 4A, the device of
the present invention is shown to include flexible, biologically
compatible material. The device 10 is generally a knit material
having upper and lower ends 12, 14. In one embodiment, the device
10, 10' defines an internal volume 16, 16' which is completely
enclosed but for the open ends 12, 12' and 14'. In the embodiment
of FIG. 3, lower end 14 the device encloses the apex of the heart.
In the embodiment of FIG. 4, lower end 14' is open, i.e., the apex
of the heart protrudes beyond the lower end 14' of the device. In
both embodiments, upper ends 12, 12' are open. Elements in common
between the figures are numbered identically with the occasional
addition of an apostrophe to distinguish one embodiment from
another. Such elements need not be separately discussed.
[0070] The device 10 is dimensioned with respect to a heart H to be
treated. Specifically, the device 10 is sized for expansion of the
heart H to be constrained. The device 10 has a length L between the
upper and lower ends 12, 14 sufficient for the device 10 to
constrain the left or right (or both) ventricular lower extremities
of the heart H. The upper end 12 of the jacket 10 extends up to,
and if desired, to include, the valvular annulus VA. Where it is
desired to constrain enlargement of the upper portion UP, the
device 10 may be extended to cover the upper portion UP. In a
preferred embodiment, the device 10 is sized so that the upper end
12 can reside in the A-V groove AVG.
[0071] Sizing the device 10 for the upper end 12 to terminate at
the A-V groove AVG is desirable for a number of reasons. First, the
groove AVG is a readily identifiable anatomical feature to assist a
surgeon in placing the device 10. By placing the upper end 12 in
the A-V groove AVG, the surgeon is assured the device 10 will
provide sufficient support at the valvular annulus VA. The A-V
groove AVG and the major vessels act as natural stops for placement
of the device 10 while assuring coverage of the valvular annulus
VA. Using such features as natural stops is particularly beneficial
in minimally invasive surgeries where a surgeon's vision may be
obscured or limited.
[0072] After the device 10 is positioned on the heart H as
described above, the device 10 is secured to the heart. Preferably,
the device 10 is secured to the heart H through sutures. The device
10 is sutured to the heart H at suture locations 15
circumferentially spaced along the upper end 12 and along or
proximate the septal wall.
[0073] To permit the device 10 to be easily placed on the heart H,
the material of the device 10 is preferably larger than the lower
portion LP of the heart H during diastole. So sized, the device 10
may be easily applied to the heart H. Once secured, the device 10
may be adjusted to snugly conform to the external geometry of the
heart H during diastole. Such sizing is easily accomplished due to
the knit construction of the device 10. For example, excess
material of the jacket 10 can be gathered and sutured S'' (FIG. 5)
to reduce the maximum diastolic volume and conform the material to
the shape of the heart H during diastole. As an alternative to
gathering the material, the tension of the material can be adjusted
using other methods discussed below.
[0074] Variable Compliance
[0075] The device 10 described above is configured to surround at
least parts of the left and/or right ventricular chambers to
provide support at end diastole to reduce dilation associated with
heart failure. According to one embodiment of the invention, the
device 10 may be constructed such that pressure exerted by the
device on one ventricle is different than the pressure exerted by
the device on the other ventricle.
[0076] In a preferred embodiment, the device 10 of the present
invention takes into consideration the physiological differences
between the right and left ventricles RV and LV (i.e., the right
ventricular wall is generally about half the thickness of the left
ventricular wall and the pressure in the right ventricle is
substantially lower than that of the left ventricle). Because
excess pressure on the right ventricle RV may prevent filling of
the right ventricle RV, the pressure exerted by the device on the
right ventricle RV is preferably less than the end diastolic
pressure of the right ventricle RV
[0077] Generally, the end diastolic pressure of the left ventricle
is higher than the end diastolic pressure of the right ventricle.
For example, in a healthy heart, the end diastolic pressure of the
left ventricle is between about 6 mmHg and about 8 mmHg whereas the
end diastolic pressure of the right ventricle is between about 4
mmHg and about 6 mmHg. Generally, in a healthy heart, the end
systolic pressure of the left ventricle is between about 100 mmHg
and about 120 mmHg and the end systolic pressure of the right
ventricle is between about 18 mmHg and about 24 mmHg. Generally,
the end diastolic in both the right and left ventricle and atria
are higher in a diseased heart H than in a healthy heart H'.
[0078] The invention provides a device 10 in which the pressure
exerted by the device 10 on the right ventricle RV may be different
(i.e., less) than the pressure exerted by the device 10 on the left
ventricle LV. Preferably the pressure differential is feasibly
because the material of the device 10 is secured to the cardiac
surface. Although the material can be secured anywhere on the
cardiac surface, the material is preferably secured at a location
at or proximate the septal wall that separates the two ventricles.
Preferably, the material is secured via sutures that extend through
the myocardium, preferably the suture extend through the ventricle
wall.
[0079] Attachment of the material to the cardiac surface helps
disconnect the applied ventricular pressure and tension in the
material covering each ventricle such that the right ventricle and
left ventricle can achieve different diastolic pressures. Because
the left ventricle typically expands at a higher pressure than the
right ventricle, a cardiac support device (which defines a specific
volume) implanted without attachment to the cardiac surface (i.e.,
proximate the septal wall) may result in left ventricle filling at
the expense of right ventricle expansion. Such as "volume shift"
could occur even with a device constructed wherein the material
configured to cover the right ventricle has a different compliance
than the material configured to cover the left ventricle. However,
a cardiac support device constructed wherein the material designed
to cover the right ventricle has a different compliance than the
material designed to cover the left ventricle is implanted without
septal attachment may still be desirable. Although such an
embodiment may not initially address the "volume shift" phenomenon,
once fibrosis secures the material in place on the cardiac surface,
the differing compliance in the fabric would allow different
filling profiles for each ventricle.
[0080] The device may be installed as a single unitary "jacket"
configured to cover both the right and left ventricles or as one or
two or more separate components (e.g., a first component configured
to cover the right ventricle and a second component configured to
cover the left ventricle). Generally, for a unitary device, a
conical jacket is first positioned over the heart. At this time it
may be desirable to anchor the device in a few locations around the
base of the heart. The device is then secured to the heart,
preferably proximate the septal line. Once secured to the heart,
the tension of the material covering each ventricle may be
adjusted. The tension of the material covering the right ventricle
can be lower than the tension of the material covering the left, if
desired. If desired, the device can be further anchored by placing
additional sutures at the base.
[0081] Alternately, the device can be installed as two or more
separate components. According to one embodiment, a first component
(e.g., a piece of material) having a preselected size is positioned
over a first ventricle. Lateral edges of the material are attached
to the cardiac surface, preferably by sutures that extend through
the myocardium, most preferably at or proximate the septal wall.
The top and bottom of the material are also sutured to the cardiac
surface. If desired, a second component (e g., a second piece of
material) having a preselected size may be positioned over the
remaining ventricle and secured in a similar manner. In one
embodiment, the device may be implanted only over left ventricle,
leaving the right ventricle unrestricted, for example, to constrain
left ventricular expansion. Alternately, it may be desirable to
constrain the expansion of only the right ventricle, for example,
an infarcted right ventricle RV' to prevent aneurysm of the right
side, while not restraining the left ventricle LV' (e.g., if the
left ventricle is healthy). In a further embodiment, the device may
comprise a plurality of components. For example, one ventricle
(right or left, or both) may be covered with one or more pieces of
material, each having the same or different compliance.
[0082] The device 10 can be secured to the septal wall, or
proximate the septal wall, using a variety of methods, including
sutures, staples and adhesives. Actual attachment may be into or
through the septal wall S' or into or through the left ventricle
LV' near the septum. Typically, the device 10 is secured to the
septal wall using sutures. In one embodiment, the knit material of
the device 10 is sutured directly to the septal wall S'. (See FIGS.
3A and 4A) Alternately, the knit material of the device 10 may be
secured to a securing member that is then secured to the septal
wall. In one embodiment, the securing member is an inelastic band
40 that is secured to the septal wall (See FIG. 8A). In another
embodiment, the knit material of the device 10 is secured to rings
50 of a material, for example, plastic, metal or fabric rings 50,
wherein the rings 50 are then secured to the setpal wall (See FIG.
9A).
[0083] The pressure differential between the material covering the
right and left ventricles can be achieved in a variety of ways. In
one embodiment of the invention, the pressure differential is
achieved by constructing the device using two types of material,
one with a higher compliance than the other. A first piece of
material is secured along or proximate the septal wall to cover one
ventricle and a second piece of material is secured along or
proximate the septal wall to cover a second ventricle.
[0084] According to one embodiment, the material covering the right
ventricle RV is more compliant than the material covering the left
ventricle LV. As used herein, the term "compliant " refers to a
material that can expand in response to a force. "Compliance"
refers to the displacement (in inches or centimeters) or strain
(inches/inch or cm/cm) per a unit load (in pounds or kilograms) or
load per unit width (in pounds per inch or kilograms per
centimeter) for a material. A material that is more compliant is
displaced further per unit load than a material that is less
compliant. The compliance of the material may be due to a variety
of factors, including, but not limited to, the compliance of the
individual filaments 30 that make up the fibers 20, the relative
movement of the filaments 30 within a fiber 20, and/or the relative
movement of the intertwined fibers 20 when subjected to load. (See
FIG. 6)
[0085] In one embodiment of the invention, the material covering
the right ventricle is more compliant than the material covering
the left ventricle. For example, the multiaxial expansion of the
material covering the right ventricle may be between about 20% and
30% when exposed to a load between about 1 pounds per inch (1.8
N/cm) and about 3 pounds per inch (5 N/cm) whereas the material
covering the left ventricle may have a multiaxial expansion between
about 10% and 20% when exposed to the same load. The term
"multiaxial expansion" refers expansion of a material along at
least a first and a second axis and includes expansion along more
than two axes.
[0086] In another embodiment, the pressure differential is achieved
by having the tension of the material covering the left ventricle
LV greater than the tension of the material covering the right
ventricle RV. The tension of the material can be modified using a
variety of methods. In one embodiment, various sized materials are
prepared such that different sized pieces of material are used for
different predetermined cardiac expansion sizes or expansion
ranges. "Predetermined size" refers to the predetermined expansion
limit of the material that circumferentially constrains cardiac
expansion during diastolic filling of the heart.
[0087] Alternately, the material can include a mechanism for
selectively adjusting the size of the material. Advantageously,
such an adjustment mechanism can be used initially to set the
tension of the material covering each ventricle, and also
subsequently to readjust the amount of cardiac reinforcement as
therapeutic reduction of cardiac expansion occurs. In one
embodiment, the material covering one or both of the ventricles can
be gathered and secured, for example, by suturing. (See FIG. 5)
[0088] According to another embodiment, an inflatable member is
mounted between the material covering one of the ventricles and the
epicardium. A separate inflatable member can be mounted between the
material covering the other ventricle if desired. Alternately, an
inflatable member may only be mounted between the material covering
one ventricle and the ventricular epicardium. Inflating the
inflatable member through an inflation port with, for example, a
gas or a liquid can increase the tension of the material. Inflation
of the inflatable member provides an increase in the tension of the
material covering the ventricle.
[0089] Another mechanism for selectively adjusting the tension of
the material can include a slot that opens at the base of the
jacket and extends towards the apex. The slot includes opposing
lateral edges. By adjusting the proximity of the opposing lateral
edges, the tension of the material can be varied. Moving the
opposing edges of the slot closer together narrows the slot and
increases the material tension. The opposing edges of the slot can
be fastened together at a predetermined proximity by, for example,
one or more lateral attachment devices, such as a cord, suture,
band, adhesive or shape memory element attached to each lateral
edge.
[0090] Material
[0091] As mentioned, the jacket 10 is constructed from a knit,
biocompatible material. The knit 18 is illustrated in FIG. 6.
Preferably, the knit is a so-called "Atlas knit" well known in the
fabric industry. The Atlas knit is described in Paling, Warp
Knitting Technology, p. 111, Columbine Press (Publishers) Ltd.,
Buxton, Great Britain (1970).
[0092] The Atlas knit is a knit of fibers 20 having directional
expansion properties. More specifically, the knit 18, although
formed of generally inelastic fibers 20, permits a construction of
a flexible fabric at least slightly expandable beyond a rest state.
FIG. 6 illustrates the knit 18 in a rest state. The fibers 20 of
the fabric 18 are woven into two sets of fiber strands 21a, 21b
having longitudinal axes X.sub.a and X.sub.b . The strands 21a, 21b
are interwoven to form the fabric 18 with strands 21a generally
parallel and spaced-apart and with strands 21b generally parallel
and spaced-apart.
[0093] For ease of illustration, fabric 18 is schematically shown
in FIG. 7 with the axis of the strands 21a, 21b only being shown.
The strands 21a, 21b are interwoven with the axes Xa and Xb
defining a diamond-shaped open cell 23 having diagonal axes A.sub.m
In a preferred embodiment, the axes A.sub.m are 5 mm in length when
the fabric 18 is at rest and not stretched. The fabric 18 can
stretch in response to a force. For any given force, the fabric 18
stretches most when the force is applied parallel to the diagonal
axes A.sub.m The fabric 18 stretches least when the force is
applied parallel to the strand axes X.sub.a and X.sub.b The jacket
10 is constructed for the material of the knit to be directionally
aligned for a diagonal axis A.sub.m to be parallel to the heart's
longitudinal axis AA-BB
[0094] While the jacket 10 is expandable due to the above described
knit pattern, the fibers 20 of the knit 18 are preferably
non-expandable. While all materials expand to at least a small
amount, the fibers 20 are preferably formed of a material with a
low modulus of elasticity. In response to the low pressures in the
heart H during diastole, the fibers 20 are non-elastic. In a
preferred embodiment, the fibers are 70 Denier polyester. While
polyester is presently preferred, other suitable materials include
polytetrafluoroethylene (PTFE), expanded PTFE (ePTFE),
polypropylene and stainless steel.
[0095] The knit material has numerous advantages. Such a material
is flexible to permit unrestricted movement of the heart H (other
than the desired support on circumferential expansion). The
material is open defining a plurality of interstitial spaces for
fluid permeability as well as minimizing the amount of surface area
of direct contact between the heart H and the material of the
jacket 10 (thereby minimizing areas of irritation or abrasion) to
minimize fibrosis and scar tissue.
[0096] The open areas of the knit construction also allows for
electrical connection between the heart and surrounding tissue for
passage of electrical current to and from the heart. For example,
although the knit material is an electrical insulator, the open
knit construction is sufficiently electrically permeable to permit
the use of trans-chest defibrillation of the heart. Also, the open,
flexible construction permits passage of electrical elements (e.g.,
pacer leads) through the jacket. Additionally, the open
construction permits other procedures, e.g., coronary bypass, to be
performed without removal of the jacket.
[0097] A large open area for cells 23 is desirable to minimize the
amount of surface area of the heart H in contact with the material
of the jacket 10 (thereby reducing fibrosis). However, if the cell
area 23 is too large, localized aneurysm can form. Also, a strand
21a, 21b can overly a coronary vessel with sufficient force to
partially block the vessel. A smaller cell size increases the
number of strands thereby decreasing the restricting force per
strand. Preferably, a maximum cell area is no greater than about 9
mm.sup.2 (about 3 mm by 3 mm) and, more preferably, is about 5.8
mm.sup.2 (about 2.4 mm by 2.4 cm). The maximum cell area is the
area of a cell 23 after the material of the jacket 10 is fully
stretched and adjusted to the maximum adjusted volume on the heart
H as previously described.
[0098] The fabric 18 is preferably tear and run resistant. In the
event of a material defect or inadvertent tear, such a defect or
tear is restricted from propagation by reason of the knit
construction.
[0099] With the foregoing, a device and method have been taught to
treat cardiac disease. The jacket 10 constrains further undesirable
circumferential enlargement of the heart while not impeding other
motion of the heart H. With the benefits of the present teachings,
numerous modifications are possible. For example, the jacket 10
need not be directly applied to the epicardium (i.e., outer surface
of the myocardium) but could be placed over the parietal
pericardium. Further, an anti-fibrosis lining (such as a PTFE
coating on the fibers of the knit) could be placed between the
heart H and the jacket 10. Alternatively, the fibers 20 can be
coated with PTFE.
[0100] The jacket 10 is low-cost, easy to place and secure, and is
susceptible to use in minimally invasive procedures. The thin,
flexible fabric 18 permits the jacket 10 to be collapsed and passed
through a small diameter tube in a minimally invasive
procedure.
[0101] The jacket 10 can be used in early stages of congestive
heart disease. For patients facing heart enlargement due to viral
infection, the jacket 10 permits support of the heart H for a
sufficient time to permit the viral infection to pass. In addition
to preventing further heart enlargement, the jacket 10 treats
valvular disorders by constraining circumferential enlargement of
the valvular annulus and deformation of the ventricular walls.
[0102] The jacket 10, including the knit construction, freely
permits longitudinal and circumferential contraction of the heart H
(necessary for heart function). Unlike a solid wrap (such as a
muscle wrap in a cardiomyoplasty procedure), the fabric 18 does not
impede cardiac contraction. After fitting, the jacket 10 is
inelastic to prevent further heart enlargement while permitting
unrestricted inward movement of the ventricular walls. The open
cell structure permits access to coronary vessels for bypass
procedures subsequent to placement of the jacket 10. Also, in
cardiomyoplasty, the latissimus dorsi muscle has a variable and
large thickness (ranging from about 1 mm to 1 cm). The material of
the jacket 10 is uniformly thin (less than 1 mm thick). The thin
wall construction is less susceptible to fibrosis and minimizes
interference with cardiac contractile function.
[0103] In addition to the foregoing, the present invention can be
used to reduce heart size at the time of placement in addition to
preventing further enlargement. For example, the device can be
placed on the heart and sized snugly to urge the heart to a reduced
size. More preferably, the heart size can be reduced at the time of
jacket placement through drugs (e.g., dobutamine, dopamine or
epinephrine or any other positive inotropic agents) to reduce the
heart size. The jacket of the present invention is then snugly
placed on the reduced sized heart and prevents enlargement beyond
the reduced size.
[0104] From the foregoing, a low cost, reduced risk method and
device are taught to treat cardiac disease. The invention is
adapted for use with both early and later stage congestive heart
disease patients. The invention reduces the enlargement rate of the
heart as well as reducing cardiac valve regurgitation.
* * * * *