Surgery – Internal organ support or sling
Reexamination Certificate
1998-02-13
2001-05-01
Willse, David H. (Department: 3738)
Surgery
Internal organ support or sling
Reexamination Certificate
active
06224540
ABSTRACT:
BACKGROUND OF THE INVENTION
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 failing 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. Table 1 lists a number of developed devices with pertinent operating characteristics.
TABLE 1
Pul-
Blood
sa-
Con-
Level of
til-
tact-
Device
Support
ity
Duration
ing
Comments
IABP
Partial <20%
Y
Days to
Y
Counter-
Months
pulsation
provides LV
unloading
Biopump
Full
N
Days
Y
Limited to
short duration
due to
thrombotic
potential
Thoractec
Full
Y
Months
Y
Sac-type
actuation
Novacor
Full
Y
Months
Y
Sac-type
pump with
electric
actuation
Hemopump
Partial
N
Days
Y
Axial flow
50-75%
pump
Heart Mate
Full
Y
Months
Y
Pusher-Plate
pneumatic and
electric
Aortic Patch
Partial
Y
Months
Y
Counter-
pulsation
BVS 5000
Full
Y
Weeks
Y
Designed for
temporary
support
Anstadt
Full
Y
Days
N
Cardiac
resuscitation
Cardio-
Partial
Y
Years
N
Requires
myoplasty
<20%
muscle training
One, more recent development 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.
It is an object of this invention to provide a completely passive girdle to be wrapped around a heart suffering from ventricular dilatation to limit this dilatation and thus improve the performance characteristics of the heart.
It is another object of this invention to provide a passive girdle or vest which can, over a period of time, have its diameter decreased to effect some decrease in dilatation of the ventricle.
Other objects will become apparent in accordance with the description of the preferred embodiments below.
SUMMARY OF THE INVENTION
Ventricular dilatation is a clinically dangerous condition for end stage cardiac failure patients. The output of the heart is effected by: (a) end-diastolic volume (ventricular volume at the end of the filling phase), (b) end-systolic volume (ventricular volume at the end of the ejection phase), and (c) heart rate. When (a) is very large, (b) also tends to be larger and (c) tends to be larger than normal. All three of these factors contribute to large increases in the tension-time integral and therefore to increased oxygen consumption.
Only a small amount of the energy consumed by the heart is used to do mechanical work. For example, with a cardiac output of 5 liters/minute, and &Dgr;p of 100 mm(Hg), the mechanical work done by the left ventricle is about 1.1 watts, and that of the right ventricle is about 0.2 watts. This compares with the typical total energy consumed by the heart (mechanical work during systole plus the energy cost in maintaining elastic tension during diastole) of about 13.2 to 15 watts.
Thus, since cardiac efficiency (typically between 3% and 15%) is defined as the ratio of the mechanical work done by the heart to the total energy (or load of the heart muscle): then,
Cardiac Efficiency,
η
=
∫
P
v
ⅆ
V
∫
P
ⅆ
V
+
k
∫
T
ⅆ
t
(
1
)
P
V
: Ventricle Pressure
P: Pressure
V: Volume
T: Tension
t: Time
The constant K accounts for conversion of units.
An increase in mechanical work by a large factor results in a small increase in oxygen consumption but an increase in tension time causes a large increase in oxygen consumption. Patients with dilated ventricles who have undergone active cardiomyoplasty have not been reported to show any objectively measurable hemodynamic improvement.
Broadly speaking in the present invention a completely passive girdle is wrapped around the ventricle or the entire heart muscle, and sized so that it constrains the dilatation during diastole and does not effect the action of the ventricle during systole. With the present surgical techniques, it is expected initial access to the heart to place the girdle in position, will require opening the chest. However, it may be possible to locate a girdle in position without thoracotomy. In one embodiment, a synthetic girdle made from material that can limit tension, but is otherwise deformable to conform to the anatomical geometry of the recipient heart is used. This girdle may be adjustable in size and shape over an extended period of time in order to gradually decrease the ventricular dilatation. A second embodiment employs a fluid filled passive wrap constructed of a series of horizontal sections. This provides for a variable volume to be enclosed by the wrap with volume control being obtained by controlling the volume of fluid from an implantable reservoir within the body. In its most preferable form, this passive wrap can be formed of a series of horizontal tubular segments each individually sealed and attached to one another along the long axis of the cylinder. If the cylinders are made of indistensible material, then changing the volume of fluid from the cylinders being in a substantially deflated condition to one where they are partially or fully inflated, decreases the internal perimeter of the wrap or girdle, thereby decreasing the effective radius of the girdle around the heart. Another feature of the invention is a feedback system, wherein sensors, for example, strain gauges, can be built into an indistensible lining to measure its tension and thereby provide automatic feedback to a hydraulic circuit controlling the wrap volume.
To avoid the problem of potential irritability and damage to the external myocardium cells by virtue of the artificial wrap and its long term constraining contact with the myocardium, one embodiment of the invention employs a tissue engineered lining to protect the myocardium. This tissue engineered lining consists of a polymer scaffold seeded with myocardial cells harvested from the patient's own myocardium using tissue engineering technology. That lining then generates a biological myocardio-interfacing surface and remains firmly attached to the polymer interfacing with the surface from which the wrap is made. Such a lining would integrate biologically to the heart's myocardial cells in a manner analogous to other devices currently being investigated which use cell scaffolds for in vitro and in vitro tissue engineering.
REFERENCES:
patent: 2826193 (1958-03-01), Vineberg
patent: 3464322 (1969-09-01), Pequignot
patent: 3587567 (1971-06-01), Schiff
patent: 3613672 (1971-10-01), Schiff
patent: 4536893 (1985-08-01), Parravicini
patent: 4628937 (1986-12-01), Hess et al.
patent: 4690134 (1987-09-01), Snyders
patent: 4827932 (1989-05-01), Ideker et al.
patent: 4936857 (1990-06-01), Kulik
patent: 4957477 (1990-09-01), Lundbäck
patent: 5098369 (1992-03-01), Heilman et al.
Kung Robert T. V.
Lederman David M.
Abiomed, Inc.
Engelenner Thomas J.
Nutter & McClennen & Fish LLP
Willse David H.
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