Method of making a left ventricular assist device

A method of making a left ventricular assist device (LVAD) using muscle wrapped around a mandrel to form a muscle pouch, the open end of which is sewn to a circular sheet of patch material having connections to one end of each of a pair of vascular grafts, or alternatively to one end of a single vascular graft. The second ends of these vascular grafts are used to connect the LVAD to the aorta. After the muscle pouch has been formed around the mandrel, the mandrel is removed and replaced by a balloon which is inserted into the muscle pouch and inflated to maintain the desired shape of the muscle pouch during healing and stimulation of the pouch. The balloon is subsequently removed preceding activation of the LVAD to allow it to begin pumping blood. In an alternative embodiment, an additional strip of latissimus dorsi or other appropriate muscle or a mechanical clamping device may be used to synchronously compress the aorta between the ends of the vascular grafts anastomosed to the aorta.

FIELD OF INVENTION 
This invention relates to the field of left ventricular assist devices. 
BACKGROUND OF THE INVENTION 
Left Ventricular Assist Devices (LVADs) are auxiliary pouches intended to 
function as booster pumps to aid the hearts of individuals suffering from 
chronic congestive heart failure. This condition is frequently due to 
heart attacks that reduce the pumping capacity of the human heart. By 
boosting the capacity of such a weakened heart, individuals suffering from 
this condition may be allowed to again lead relatively normal, effective 
lives. 
While various designs of LVADs have been proposed, the most promising 
appears to be an auxiliary pouch formed from the individual's latissimus 
dorsi muscle and controlled by a pacemaker. This approach avoids potential 
rejection problems related to the use of other non-autologous materials 
and takes advantage of well-developed pacemaker and prosthetic vascular 
graft technology. LVADs of this type are commonly called skeletal muscle 
ventricles (SMVs). Much of the developmental work on these devices has 
been accomplished by Dr. Larry Stephenson and colleagues at Wayne State 
University. Their work has been described in various articles in the 
literature; see, for example, 1) Clark M, Springen K, Help For The Heart: 
Back Muscle. Newsweek Dec. 22, 1986. 2) Mannion JD et al., Hydraulic 
pouches of canine latissimus dorsi: Potential for left ventricular 
assistance. Journal of Thoracic Cardiovascular Surgery 1986; 91:534-544. 
3) U.S. Pat. No. 4,979,936. 4) Thomas GA et al. Pericardium-Lined Skeletal 
Muscle Ventricles in Circulation up to 589 Days. Society of Thoracic 
Surgeons 1994; 58:1-11. 
Based on development work done previously on beagles, it is anticipated 
that the procedure for creating such an SMV in a human would involve 
making an incision to expose the left latissimus dorsi muscle and 
dissecting the muscle free from the subcutaneous tissues and chest wall, 
except for the neurovascular bundle and humeral insertion. A bipolar nerve 
cuff electrode is placed around the thoracodorsal nerve. The nerve lead is 
connected to an inactive neurostimulator, buried beneath the left rectus 
abdominis muscle, which innervates the exposed latissimus dorsi muscle. 
Next, the left chest is opened at the fourth rib. Preferably, the fourth 
rib is removed to provide more space for the LVAD. Optionally, the 
anterior pericardium is removed between the phrenic nerves and used to 
cover a conically-shaped mandrel of biocompatible plastic. Mandrels used 
for beagles had a diameter of about 3 cm, length of about 6.5 cm and 
volume of about 25 ml; a mandrel suitable for forming a human SMV would 
need to be appropriately enlarged. After wrapping the pericardium around 
the mandrel it is sewn to a 5 mm thick collar of synthetic material such 
as woven Dacron felt placed at the base of the mandrel. The dorsal edge of 
the latissimus dorsi muscle is then folded longitudinally upon itself and 
secured by sutures, after which the medial aspect of the latissimus dorsi 
muscle is wrapped around the mandrel (and over the pericardium if it was 
used) about 2-2.5 times with the folded edge of the muscle sewn 
circumferentially to the Dacron felt collar. The SMV is then positioned 
subcutaneously and the wound is closed and allowed to heal for three 
weeks. 
Following this healing period, the neurostimulator is activated to deliver 
continuously a 2 Hz stimulation of 210 microsecond duration and 1 to 2 
volt amplitude. The purpose of the stimulation is to transform the 
fatigable Type II latissimus dorsi muscle fibers to fatigue-resistant Type 
I muscle fibers. Typically, 6 weeks are allowed for this stimulation 
period, after which the chest is again opened to connect the formed muscle 
pouch to the aorta. This is accomplished by first attaching sensing leads 
to the left ventricle. The descending thoracic aorta is exposed to allow 
two 12 mm ringed vascular grafts to be anastomosed to the aorta, one above 
the other, in end-to-side fashion. 
After completion of these anastomoses, a cotton tape is passed around the 
aorta between the two graft anastomoses for subsequent ligation of the 
aorta. Next, a circular 3.5 cm diameter piece of patch material is cut 
from a sheet of 0.6 mm thick GORE-TEX.RTM. Cardiovascular Patch. This 
circular piece may optionally be formed into a concave, cup-like shape. A 
pair of 12 mm diameter holes are cut through this sheet to accommodate 
anastomosis of the opposite ends of the two vascular grafts. The plastic 
mandrel is removed from within the muscle pouch. The Dacron felt collar 
remains. The 3.5 cm diameter circular piece of GORE-TEX Cardiovascular 
Patch is sewn over the open end of the muscle pouch (with the concave side 
facing the pouch if the patch was so formed) and the opposite ends of the 
two vascular grafts are anastomosed to the 12 mm diameter holes in the 
patch. The aorta is then at least partially ligated forcing blood flow 
through the newly formed SMV. Finally, the nerve lead and myocardial leads 
are connected to an R-wave synchronous pulse-train stimulator. 
Alternatively, the vascular grafts may be provided with valves (such as 
prosthetic heart valves) to control the flow of blood through the LVAD. 
The use of valves may obviate the need to ligate the aorta. 
SMVs made as described above have been demonstrated to generate significant 
increases in cardiac output in Beagle dogs for periods of longer than 19 
months. While effectiveness in humans remains to be demonstrated, animal 
results thus far appear promising. 
A fundamental disadvantage of the above procedure lies in the removal of 
the plastic mandrel from the muscle pouch, sewing the patch material to 
the pouch and anastomosis of the vascular grafts to the patch material 
immediately preceding activation of the SMV. The needle punctures 
immediately preceding exposure of the SMV and vascular grafts to blood 
pressure often result in suture line bleeding at the patch and vascular 
graft suture lines and may result in disruption of a suture line. 
SUMMARY OF THE INVENTION 
The present invention relates to a revised LVAD procedure wherein after 
forming the SMV around the plastic mandrel, the mandrel is replaced by an 
inflatable balloon of biocompatible material which, after inflation, is 
used to maintain the shape of the SMV during healing and stimulation 
period during which the SMV is converted from the fatiguable Type II 
muscle fibers to fatigue-resistant Type I muscle fibers. The use of a 
balloon allows for an increased amount of the construction of the LVAD to 
be performed during the initial surgery. According to one embodiment, 
virtually the entire LVAD can be constructed during the first surgery. In 
addition to allowing for more complete healing of the LVAD before it is 
used for pumping blood, the stimulation period is anticipated to be more 
effective because the SMV is working dynamically against an inflated 
balloon rather than isometrically against a rigid mandrel. 
According to the method of the present invention, the muscle pouch is 
formed and sewn around the plastic mandrel. The mandrel is then removed 
and the muscle pouch is sewn to a circular piece of patch material that 
incorporates one or two vascular grafts previously anastomosed to the 
circular piece of patch material in a leak-proof fashion. The inflatable 
balloon is then introduced into the muscle pouch via one of the vascular 
grafts and inflated by a small conduit for the balloon extending through 
the vascular graft and connecting to the balloon within the muscle pouch. 
Again via the small conduit, the balloon can be deflated after the three 
week healing period and six week stimulation period, and removed from 
within the muscle pouch via the end of the vascular graft opposite the 
muscle pouch. In addition to allowing for nine weeks of healing of the 
seam line between the circular patch and muscle pouch, the inventive 
process also simplifies the second surgery in that essentially only 
removal of the balloon, anastomosis of the grafts, ligation of the aorta 
and connection of the nerve and myocardial leads to the stimulator are 
required prior to activation of the SMV. 
In an alternative embodiment, the anastomoses of the one or two vascular 
grafts to the aorta are performed during the first surgery. The vascular 
graft or grafts are maintained in an occluded state during the healing and 
stimulation period by the use of balloons. The vascular graft occlusion 
balloon or balloons are deflated and removed following this period along 
with the balloon used to maintain the shape of the SMV during the healing 
and stimulation period, for example, from a small opening in the end of 
the SMV opposite the end sewn to the circular patch material. This may be 
accomplished through a small subcutaneous incision to provide the 
necessary access; the small opening in the end of the SMV is then closed 
prior to activation of the LVAD. Alternatively the balloon may be removed 
through one of the vascular grafts. Such methods eliminate the need to 
perform a second major surgery in order to anastomose the vascular graft 
or grafts to the aorta. 
While latissimus dorsi muscle is conventionally used to form the muscle 
pouch (optionally over a layer of pericardium), it is believed that it may 
be possible to use other Type II muscles as well. 
Further, the circular patch material sewn to the base of the muscle pouch 
may be provided with two or three flanges around the circumference of the 
patch if it is desired to use pericardium, a covering layer of synthetic 
material such as GORE-TEX.RTM. Preclude Pericardial Membrane, or both in 
addition to the latissimus dorsi muscle. The use of such a synthetic 
material may be desirable to help prevent adhesion of surrounding tissue 
to the exterior of the SMV. By providing the circular patch material with 
two or more circumferential flanges, the various individual layers forming 
the SMV may be sewn to the patch between the adjacent circumferential 
flanges of the patch. 
In another embodiment, intermittent ligation of the aorta may be 
accomplished by the use of a separate strip of latissimus dorsi muscle 
wherein the end of the strip wraps around the aorta in place of the 
conventional ligation. This end of the latissimus dorsi muscle strip can 
then compress the aorta to cause closure of the aortic passageway between 
the vascular grafts. This can be done cyclically with activation of the 
SMV so that the aorta will be closed by the latissimus dorsi muscle strip 
only during systolic action of the SMV. In the event of functional failure 
of the SMV, the strip of latissimus dorsi muscle would be relaxed by 
deactivating the neurostimulator. Alternatively, a mechanical clamping 
device may be used to effect ligation of the aorta, either cyclically or 
continuously, during use of the SMV and deactivated to release clamping of 
the aorta in the event of failure of the SMV. Sensing systems to actuate 
such a mechanical clamp are known in the fields of pacemakers and 
defibrillators.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 describes a typical LVAD 10 as made by either the prior art 
procedure or by the inventive procedure, wherein an SMV 12, formed 
previously around a temporary mandrel to create a cavity 14, is connected 
to a patient's aorta 16 by ends 23 and 26 of vascular grafts 21 and 24. 
Opposing first ends 22 and 25 of vascular grafts 21 and 24 are sewn to a 
synthetic sheet of circular patch material 32 which is in turn sewn to SMV 
12 at suture line 34. Ligation 37 is placed about the aorta 16 between 
adjacent second ends 23 and 26 of vascular grafts 21 and 24 so that the 
flow of blood from the heart 18 is routed through the SMV 12. Pulsing of 
the SMV 12 is controlled by burst pulse generator 36 connected to the 
heart 18 and the thoracodorsal nerve 38. 
The method of the prior art requires two surgical procedures to create the 
LVAD 10. The first surgery involves wrapping the freed end of the strip of 
latissimus dorsi muscle around a plastic mandrel to form the SMV. The 
second surgery to remove the mandrel from the SMV 12 includes the 
subsequent steps of sewing the circular patch material 32 to the SMV 12 
and anastomosing the vascular grafts 21 and 24 to aorta 16 and the 
circular patch 32. After completion of these steps the LVAD is activated 
before closing the patient's chest. Because all of these various suture 
lines are created immediately preceding exposure of the LVAD to blood 
pressure and mechanical stress from the pulsing of the SMV 12, it is 
apparent that bleeding of the suture lines must be dealt with before the 
patient can be closed. Further, there is a substantial risk of disruption 
of this suture line in the first week following surgery, before 
significant healing of this suture line has had time to occur. 
The method of the present invention is described beginning with FIG. 2A 
which describes the step of wrapping the latissimus dorsi muscle 62 around 
the mandrel 41; typically 2-2.5 wraps of latissimus dorsi muscle are used. 
FIG. 2B describes an alternative whereby a sheet of anterior pericardium 
42, previously removed from between the phrenic nerves, is wrapped around 
mandrel 41 prior to wrapping the latissimus dorsi muscle 62 around mandrel 
41 to create the SMV 12. As shown by FIG. 3, after the SMV 12 has been 
completed by sewing the latissimus dorsi muscle 62 to itself, mandrel 41 
is removed from the SMV 12. 
FIG. 4A describes a view of SMV 12 after removal of mandrel 41 and 
attachment of assembly 50 by sewing. Assembly 50 comprises vascular grafts 
21 and 24 anastomosed to a piece of circular patch material 32 preferably 
in a leak-proof fashion whereby the anastomoses do not leak blood. Various 
methods of creating such a leak-proof assembly 50 are known. For example, 
porous PTFE vascular grafts may be anastomosed to porous PTFE patch 
material using porous PTFE sutures and the resulting suture line may be 
sealed with a medical grade silicone adhesive. Alternatively the suture 
line may be sealed by the use of a porous PTFE tape heat-sealed over the 
material edges adjacent to the seam line. According to still another 
alternative, a bifurcated vascular graft may be used wherein the large 
diameter portion of the graft is cut short and optionally deformed by 
flaring to provide the circumferential edge to be sewn to the SMV 12. 
Porous PTFE vascular grafts, cardiovascular patches and sutures are 
available from W. L. Gore and Associates, Flagstaff, Ariz. under the 
GORE-TEX.RTM. trademark. Porous PTFE materials of this type have a 
microstructure of nodes interconnected by fibrils and are made generally 
as described by U.S. Pat. Nos. 3,953,566 and 4,187,390 to Gore. 
The edge of circular patch 32 is sewn at suture line 34 to the latissimus 
dorsi muscle 62 and to the pericardium 42 if pericardium is used. 
FIG. 4B describes a cross sectional view of an alternative embodiment of 
the SMV 12 and attached assembly 50. In this embodiment the circular patch 
32 has a pair of flanges 51 and 53 about its peripheral edge whereby inner 
flange 51 is sewn to the optional pericardium 42 and outer flange 53 is 
sewn to the latissimus dorsi muscle 62. Flanged patches of this type may 
be made by laminating sheets of porous PTFE together under heat and 
pressure while keeping the sheets separated at the edges during lamination 
to form the flanges. A ring of polyamide film such as Kapton (DuPont de 
Nemours, Wilmington, Del.) may be used temporarily as a separator during 
the lamination process. Alternatively the sheets may be laminated using a 
suitable adhesive such as medical grade silicone adhesive or a 
thermoplastic adhesive such as fluorinated ethylene propylene (FEP). 
Methods of making laminated porous PTFE articles are also taught by U.S. 
Pat. Nos. 4,385,093 and 4,478,665 to Hubis. Any method may be used as long 
as the resulting article is biocompatible and the laminations do not 
separate during use. 
FIG. 5 shows the insertion of deflated balloon 45 into the SMV 12 via 
either vascular graft 21 or 24. Also as shown by this figure, after 
inflation of the balloon using syringe 47 via connecting tube 46, the 
inflated balloon 44 maintains the desired shape for the SMV 12. The 
balloon may be inflated using various media such as air, water or saline. 
The balloon may be made from any mechanically suitable biocompatible 
material; smaller balloons are used routinely in, for example, balloon 
catheters. 
FIG. 6 shows the completed LVAD 10 at the conclusion of the first surgery. 
Suture line 34 between patch 32 and the SMV 12 is allowed to heal during 
the initial three week healing period and subsequent six week stimulation 
period required for conversion of the fatigable Type II latissimus dorsi 
muscle to fatigue-resistant Type I muscle fibers. Second ends 23 and 26 of 
vascular grafts 21 and 24 are simply clamped off during this period. 
In the subsequent second surgery, inflated balloon 44 is deflated 45 and 
removed via either vascular graft 21 or 24 through which it had previously 
been inserted. The cavity 14 of the SMV 12 may be visually inspected if 
desired by an endoscope inserted into the cavity 14 via vascular graft 21 
or 24. As shown by FIG. 1, second ends 23 and 26 of vascular grafts 21 and 
24 are anastomosed to aorta 16 which is then provided with ligation 37. 
The electrode leads are connected to generator 36, after which the 
generator is activated to begin function of the LVAD. 
FIG. 7A describes an alternative embodiment wherein a separate strip 72 of 
latissimus dorsi muscle is wrapped around the aorta 16 between vascular 
graft second ends 23 and 26 and attached back to itself. Contraction of 
the strip 72 of latissimus dorsi muscle results in compression of aorta 16 
as shown by FIG. 7B. This muscle strip 72 is intended to function 
synchronously with SMV 12 to cause external compression and at least 
partial occlusion of the aorta coordinated with contraction of the SMV. 
Optionally, muscle strip 72 may be provided with a protective tubular 
covering intended to prevent adhesions from surrounding tissue, the 
covering being placed coaxially about strip 72. 
As described by FIGS. 8A and 8B it is envisioned that both of the 
alternative functions of the separate muscle strip 72 shown by FIGS. 7A 
and 7B may be accomplished by mechanical clamping device 82 (preferably 
pneumatic or hydraulic) controlled by a pacemaker or defibrillator type of 
generator depending on whether clamping device is desired to function 
simultaneously with the LVAD or in the event of failure of the LVAD. 
Alternatively, the mechanical clamping device 82 may be controlled to 
accomplish both of these functions. Optionally, the aorta 16 may be 
protected by a thin layer of protective synthetic material underneath the 
mechanical clamping device 82 where the device 82 is attached to the aorta 
16. 
In still another alternative shown by FIG. 9, the vascular grafts 21 and 24 
may be provided with valves 91 to control the direction of blood flow 
through the LVAD 10. Prosthetic heart valves of suitable diameter for the 
vascular grafts may be used as the valves 91. The use of valves 91 may 
eliminate the need to ligate the aorta. 
FIG. 10 describes another alternative whereby a prosthetic heart valve 91 
may be fitted into the aorta 16 between the anastomosed second ends 23 and 
26 of vascular grafts 21 and 24. In this embodiment as well, the use of 
valve 91 is anticipated to eliminate the need to ligate the aorta or to 
close it synchronously by external compression. 
Still another alternative embodiment eliminates the need for the second 
major surgical procedure. According to this embodiment the anastomoses of 
the second ends of the vascular grafts to the aorta are made prior to 
concluding the first surgery. This is possible by inserting one or more 
inflatable balloons into a small opening 110 in the apex of the SMV 12 
opposite the vascular grafts 21 and 24 as shown by FIG. 11A. Balloons 
extend into the vascular grafts to maintain them in an occluded condition 
until it is intended to activate the LVAD. Preferably, each vascular graft 
21 and 24 is occluded by an individual balloon 443 and 444 which is fitted 
into correct position lengthwise so that when inflated it fills the 
respective vascular graft with little or no extension into the aorta 16 
and without substantially interfering with aortic blood flow during the 
healing period. The position of the opposite ends of the vascular graft 
occluding balloons 443 and 444 is less critical but should be near or 
slightly protrude into the SMV 12. After the vascular graft occluding 
balloons 443 and 444 are correctly positioned and inflated via their 
inflation tubes 462, third and fourth balloons 441 and 442 are placed into 
the SMV 12 and inflated via inflation tubes 460 to maintain the shape of 
the SMV 12 during healing. By using third and fourth balloons 441 and 442, 
the inflation tubes 462 of the vascular graft occlusion balloons 443 and 
444 may be located between the third and fourth balloons 441 and 442 
filling the SMV 12 thereby reducing the risk of interior abrasion of the 
SMV 12 during healing and stimulation. Alternatively, a single balloon 
might be used in place of the separate third and fourth balloons 441 and 
442 if the inflation tubes 462 of the vascular graft occluding balloons 
443 and 444 are routed so as to avoid damage to the interior of the SMV 12 
during the healing and stimulation period. The inflation tubes 460 and 462 
of all four balloons 441-444 extend through the small opening 110 in the 
SMV 12, whereby they remain located subcutaneously during healing and are 
easily accessible for subsequent deflation and removal of the balloons. 
The small opening 110 may be easily closed by suturing immediately 
preceding activation of the LVAD. By this method the second major surgery 
to anastomose the vascular grafts is eliminated. 
In an alternative embodiment of the procedure described by FIG. 11A, FIG. 
11B describes a variation wherein the inflation tubes of the inflatable 
balloon or balloons extend distally through the vascular system to allow 
subsequent deflation and removal via, for example, a femoral artery. This 
alternative embodiment also allows the second ends 23 and 26 of the 
vascular grafts 21 and 24 to be anastomosed to the aorta 16 during the 
first surgery and thereby avoids the second major surgery. 
In another embodiment which is useful as a variation of the previously 
described alternatives, it is anticipated that the SMV 12 may be connected 
to the aorta 16 with a single vascular graft 20 used alternately to fill 
and discharge the SMV 12 synchronously with the function of the heart. 
This embodiment is shown generally by FIG. 12. Heart valves (not shown) 
may be used advantageously in this embodiment in similar manners to those 
shown by FIGS. 9 and 10. 
FIG. 13 describes an embodiment wherein the SMV is fashioned to function as 
an inline pump wherein the inlet and outlet vascular grafts 21 and 24 are 
at opposite ends of the SMV 12. Heart valves (not shown) may also be used 
advantageously in this embodiment in similar manners to those shown by 
FIGS. 9 and 10. 
While particular embodiments of the present invention have been illustrated 
and described herein, the present invention should not be limited to such 
illustrations and descriptions. It should be apparent that changes and 
modifications may be incorporated and embodied as part of the present 
invention within the scope of the following claims.