Surgery – Internal organ support or sling
Reexamination Certificate
1998-12-30
2003-01-21
Willse, David H. (Department: 3738)
Surgery
Internal organ support or sling
Reexamination Certificate
active
06508756
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to cardiac devices in general, and more specifically to passive and active cardiac girdles.
Patients having a heart condition known as ventricular dilatation are in a clinically dangerous condition when the patients are in an end stage cardiac failure pattern. The ventricular dilatation increases the load on the heart (that is, it increases the oxygen consumption by the heart), while at the same time decreasing cardiac efficiency. A significant fraction of patients in congestive heart failure, including those who are not in immediate danger of death, lead very limited lives. This dilatation condition does not respond to current pharmacological treatment. A small amount, typically less than 10%, of the energy and oxygen consumed by the heart, is used to do mechanical work. Thus the balance, which is the major part of the energy consumed by the heart is used in maintaining the elastic tension of the heart muscles for a period of time. With a given pressure, the elastic tension is directly proportional to the radius of curvature of the heart ventricle. During ventricular dilatation the ventricular radius increases and the energy dissipated by the heart muscle just to maintain this elastic tension during diastole is abnormally increased, thereby increasing oxygen consumption.
A number of methods and devices have been employed to aid the pumping action of failing hearts. Many of these include sacs or wraps placed around the ailing heart, or, in some instances only around the ventricle of the failing heart, with these wraps constructed to provide for active pumping usually, but not always, in synchronism with the ventricular pumping of the natural heart. A number of cardiac assist systems employing a variety of pumping approaches for assisting the pumping action of a failing natural heart have been developed. These systems include those suitable for partial to full support of the natural heart, short term (a few days) to long term (years), continuous pumping to various degrees of pulsability, and blood contacting versus non-blood contacting. Table 1 lists a number of presently developed devices with pertinent operating characteristics.
TABLE 1
Pul-
Blood
Level of
satil-
Dura-
Con-
Device
Support
ity
tion
tacting
Comments
IAPB
Partial
Y
Days to
Y
Counterpulsation
<20%
Months
provides LV unloading
Biopump
Full
N
Days
Y
Limited to short duration
due to thrombotic
potential
Thoratec
Full
Y
Months
Y
Sac-type actuation
Novacor
Full
Y
Months
Y
Sac-type pump with
electric actuation
Hemo-
Partial
N
Days
Y
Axial flow pump
pump
50-75%
Heart
Full
Y
Months
Y
Pusher-Plate pneumatic
Mate
and electric
Aortic
Partial
Y
Months
Y
Counterpulsation
Patch
BVS 5000
Full
Y
Weeks
Y
Designed for temporary
support
Anstadt
Full
Y
Days
N
Cardiac resuscitation
Cardio-
Partial
Y
Years
N
Requires muscle training
myoplasty
<20%
for active support
One, more recent development in the field of cardiomyoplasty involves the wrapping and pacing of a skeletal muscle around the heart to aid in the pumping. In that configuration, a pacemaker is implanted to control the timing of the activation of the wrapped around skeletal muscle.
A major consideration in the design of cardiac support systems is the risk of thromboembolism. This risk is most associated with use of artificial blood contacting surfaces. A variety of approaches have been employed to reduce or eliminate this problem. One approach has been the employment of smooth surfaces to eliminate potential sites for thrombi and emboli generation as well as textured surfaces to promote cell growth and stabilization of biologic surfaces. One problem affecting thromboembolism risk in heart assists arises from the use of prosthetic, biologic or mechanical pericardial valves. This risk can be some what lowered by the use of anticoagulation therapy. However, the use requires careful manipulation of the coagulation system to maintain an acceptable balance between bleeding and thromboembolic complications. The textured surface approach employs textured polyurethane surfaces and porcine valves to promote pseudo-intima formation with a stable cellular lining. While thromboembolic rates resulting from these measures are acceptable as temporary measures, improvements, particularly for implantable devices are highly desirable.
A second problem associated with implanted cardiac assist devices Is the problem of infection, particularly where the implanted device has large areas of material in contact with blood and tissue. More recently clinical protocols have improved and even the drive line and vent tubes associated with implants that require some percutaneous attachments have been manageable. However, for a ventricular assist device, quality of life considerations require that vent lines and drive lines which cross the skin barrier be eliminated thereby avoiding the encumbrance to patient activities.
A third problem area in ventricular assist devices is the calcification of these devices. This is particularly so for long term implant situations which may last five years or more. Here again the criticality of this factor is reduced for devices which do not involve direct blood contact.
Another approach employed in ventricular assist has been the development of non-pulsatile pumps. However, once again, the blood is exposed to the surfaces of the pump, particularly the bearing and seal area.
Unlike an entirely artificial heart, in which failure of the system leads to death, a ventricular assist device augments the impaired heart and stoppages should not result in death, unless the heart is in complete failure. However, for most present ventricular assist device systems, stoppage of even a few minutes results in formation of blood clots in the device, rendering any restart of the system a very risky undertaking.
SUMMARY AND OBJECTS OF THE INVENTION
According to one aspect, the present invention an artificial myocardium is constructed of an extremely pliant, non-distensible and thin material which can be wrapped around the ventricles of a natural, but diseased heart. This artificial myocardium mimics the contraction-relaxation characteristics of the natural myocardium and provides sufficient contractility, when actuated, to at least equal the contractility of a healthy natural myocardium. In this arrangement all of the direct blood contact is with the interior surfaces of the natural heart and surrounding blood vessel system. The device is hydraulically actuated in timed relationship to the contractions of the natural heart.
Using this system, the natural heart is left in place and the assist system supplies the reinforcing contractile forces required for satisfactory ventricular ejection.
A key concept for this artificial myocardium system is achieved by the realization of a controllable, artificial myocardium employing a cuff formed of a series of closed tubes connected along their axially extending walls. With sufficient hardware to hydraulically (or pneumatically) inflate and deflate these tubes, a controlled contraction is produced as a result of the geometric relationship between the length of these series of tubes in deflated condition and the length of the series of tubes when they are fluidically filled in the inflated condition. If the cuff is formed of a series of “n” tubes, each of diameter “d” when inflated, connected in series, the total perimeter length of this cuff when deflated is given by n(&pgr;d/2). However, when these tubes are filled with fluid, they have a circular cross-section such that the length of the cuff is the sum of the diameters in the individual tubes or nd. Thus the ratio of the change in perimeter length between the collapsed and the filled state is &pgr;/2. If this cuff is wrapped around the natural heart, it will, when pressurized, shorten and squeeze the heart by producing a “diastolic” to “systolic” length change of 36%. Typical sarcomere length changes are approximately 20%.
Suitable hardware, including a hydraulic pump, a compliant reservoir and rotary mechanical valve, toge
Kung Robert T. V.
Lederman David M.
Rosenberg Meir
Abiomed, Inc.
Cahill Ronald E.
Engellenner Thomas J.
Nutter & McClennen & Fish LLP
Willse David H.
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