The Artificial Heart Prototypes, Policies, and Patients (1991) / Chapter Skim
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Appendix C: Technological Opportunities and Barriers in the Development of Mechanical Circulatory Support Systems
Appendix C: Technological Opportunities and Barriers in the Development of Mechanical Circulatory Support Systems
Pages 211-250
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From page 211... ...
Mechanical circulatory support has been used in over 1,300 patients since 1985. There have been implants of approximately 186 total artificial hearts, 600 left ventricular assist devices, and 112 right ventricular assist devices along with 409 biventricular assist devices.
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From page 212... ...
Both total artificial hearts and univentricular or biventricular assist devices can be utilized temporarily for mechanical circulatory support. All of the total artificial hearts that have been utilized clinically have been pneumatically powered devices.
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From page 213... ...
Sepsis and, to some degree, thrombosis have been present in the long-term animals. The experience at Penn State for 21 consecutive pneumatic artificial heart animals indicates that 3 died from pannus formation, a proliferation of unwanted tissue in the inlet of the artificial hearts.
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From page 214... ...
The clinical registry data indicate that mechanical failure was present in 1 percent of the patients who received the total artificial heart. Similar sac-type blood pumps utilized for left ventricular assist devices have demonstrated a two year reliability in vitro (Jaszawalla et al., 1988~.
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From page 215... ...
The Penn State group has utilized an electronic automatic control system to control the devices for not only cardiac output but also actively balancing the left and right pumps. This cardiac output control system is sensitive to pump afterload, and balancing is accomplished by indirect sensing of left atrial pressure (Snyder et al., 1986~.
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From page 216... ...
As previously stated, at Penn State with a pneumatic total artificial heart, 1 animal of 21- approximately 5 percent that received the device suffered a thromboembolic event causing death. Yet evidence of thrombotic complications and organ infarction was noted in 13 of 24 calves, indicating that thrombosis is still a major complication with total artificial heart devices in animals (Al-Mondhiry et al., 19891.
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From page 217... ...
In reports from the clinical registry for the application of total artificial hearts, hemolysis was listed as a complication in 7 percent of the patients. Experience at Penn State with pneumatic artificial hearts in calves shows that compared with baseline levels, the hemoglobin was significantly lower and the plasma hemoglobin and serum lactate dehydrogenase levels significantly higher throughout the follow-up period.
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From page 218... ...
The results from the clinical registry of mechanical ventricular assistance show that bleeding and reoperation are still the major complicating factors in all pneumatic mechanical ventricular assist devices, with an incidence of
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From page 219... ...
As previously stated, thrombosis, sepsis, and to some degree hemolysis are complications associated with the application of shortterm univentricular and biventricular assist devices. Of the pulsatile ventricular assist devices, several designs and materials have been utilized.
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From page 220... ...
The electric device, in this case the Novacor device, appears to have improved results, but the device is used only for bridge to transplantation. Summary When considered as a group, short-term and long-term pneumatic and centrifugal unilateral and bilateral assist devices and total artificial hearts have complications of thrombosis, sepsis, bleeding, and hemolysis, and it is not entirely clear which will be the limiting factor in the longevity of these devices.
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From page 221... ...
Unilateral Assist Devices In Vitro and In Vivo Test Results Several groups in the United States and abroad are now working on permanent electric motor- or thermal-powered ventricular assist devices. These include Nimbus in Rancho Cordova, California, Novacor Division of Baxter Healthcare Corporation in Oakland, California, Penn State in Hershey, Pennsylvania, Thermedics in Waltham, Massachusetts, and various groups in Europe and Japan.
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From page 222... ...
The four groups supported by the National Institutes of Health for development of implantable electric motor-driven artificial hearts are the University of Utah, Nimbus/ Cleveland Clinic, ABIOMED/Texas Heart, and Penn State. There are several non-U.S.
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From page 223... ...
The distinguishing characteristics of the ABIOMED total artificial heart are as follows. · Hydraulic power generated by an electrically operated centrifugal pump energizes the blood pumps (Millner et al., 1990~.
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From page 224... ...
· Trileaflet valves and seamless blood pumps fabricated from Angioflex, a polyetherurethane, provide long life and smooth thromboresistant surfaces at affordable cost. The blood pump is toroidal in shape and may reduce flexing stresses, thus contributing to a high reliability.
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From page 225... ...
An automatic electronic control system is employed to balance both the left and right blood pumps (Rosenberg et al., 1984~. The Penn State total artificial heart system utilizes extremely smooth, seam-free blood contacting surfaces currently manufactured from either Biomer provided by Ethicon, or the segmented polyurethane Hemothane, provided by 3M Corporation, St.
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From page 226... ...
. ~ ~ _ lnermec~cs group In left ventricular assist animals and In the Penn State left ventricular assist and total artificial heart animals.
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From page 227... ...
At present, it appears that all of the groups working on electric motor-driven total artificial hearts are essentially on schedule with their program plans. The Penn State group has had two in viva experiments of a completely implanted system.
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From page 228... ...
It should be noted that both short- and long-term devices, left ventricular assist devices and total artificial hearts, may have considerably more surface area and as many as four artificial valves associated with them. It is this author's opinion that the performance of short-term mechanical circulatory assist devices in their current stage of development is comparable to that of heart valves in their early stage of development; thus, it is not unreasonable to state that these devices are currently successful but require additional development, as do current heart valves and other cardiovascular devices, to eliminate or minimize all associated complications.
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From page 229... ...
Later, Thermedics continued development of this system for application with their permanent left ventricular assist device (Sherman et al., 1983~. There have been other such systems proposed that utilize different
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From page 230... ...
At Penn State, a completely implanted electric motor-driven total artificial heart has ~ ~ .
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From page 231... ...
Thus, in summary, for the current energy converters, which include the electric motor, mechanical linkage and hydraulic pump, and the associated electronics and batteries, there do not appear to be any technological barriers that would keep these devices from functioning satisfactorily for two years with current technology; with further research and development, these times could be expanded to provide a high reliability device for five years. Thermal Heat-Cycle Energy Converters At present, two systems utilize thermal heat cycles to power mechanical circulatory support systems.
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From page 232... ...
Blood Pumps It is somewhat difficult to predict the long-term performance of blood pump sacs or diaphragms, but methods do exist. The prediction of the reliability of mechanical heart valves is more straightforward and easier to accomplish.
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From page 233... ...
The most advanced system, the Novacor system, has yet to generate sufficient in viva data to be able to accurately predict the thromboembolic complications of that device. Work at Penn State with implanted electric motor-driven total artificial hearts shows that in eight animals receiving these artificial hearts for durations up to 222 days, two had a thromboembolic event.
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From page 234... ...
Calves undergoing total artificial heart implantation have more calcification than do mature adult sheep. Very few blood pumps have been run in viva for over one year.
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From page 235... ...
Bleeding occurs in approximately 25 percent of animals undergoing implantation of ventricular assist or artificial heart devices. In the artificial heart devices, there are longer suture lines and thus bleeding becomes more probable.
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From page 236... ...
Materials Development New Plastics and Polymers One of the most widely used polymers in mechanical circulatory support systems is polyurethane, specifically Biomer, manufactured by Ethicon. This material, first developed by DuPont, is now some 20 years old.
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From page 237... ...
These composites have excellent strength-to-weight ratios and can also be manufactured of compatible biomaterials. Improved Metals, Ceramics, and Composites Improved Metals Various ferrous and nonferrous metals are utilized in the energy converters and blood pumps of MCSSs.
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From page 238... ...
New Ceramics New ceramics made of materials such as alumina, aluminum silicate, carbon/graphite, silicone nitride, titanium diboride, boron nitride, Macor from Corning Glass, partially stabilized zirconia, and others all have promising applications for mechanical components in MCSSs. One of the newest applications for these ceramics involves what are referred to as hybrid bearings.
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From page 239... ...
This material would have application in cases or housings for mechanical circulatory support systems. Electronics Development New Power Devices Over the past two decades there have been dramatic developments in electronics components.
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From page 240... ...
Through the use of new codes and supercomputers, solutions of this problem will yield basic information related to fluid mechanics and thrombosis. Numerical Analysis Techniques The ultimate longevity of the elastomeric diaphragms and other mechanical components in these blood pumps relies on an accurate prediction of the stresses imposed on the device during operation.
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From page 241... ...
Increased emphasis should be placed on the development of new biomaterials that would be applicable to mechanical circulatory assist devices and other biomedical applications.
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From page 242... ...
This model can then be utilized to understand more clearly the cardiac and vascular component actions of the drugs. Development of Transcutaneous Energy Transmission Systems Development of transcutaneous energy transmission has already been spun off into use into the cochlear implant, as previously described.
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From page 243... ...
It appears that in most instances, biventricular support or univentricular support is adequate for short-term bridge to transplant applications. With biventricular and left ventricular assist devices as successful as they are, it is doubtful that there will be an increased use of the short-term total artificial heart.
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From page 244... ...
Penn State has manufactured a complete electric motor-driven total artificial heart system that transmits energy across the intact skin by inductive coupling. The system is completely sealed and totally implantable, has undergone in vitro testing, and has been utilized in two calf experiments This system is currently in a r state of development that is equivalent to the development of long-term ventricular assist devices, with the exception of the Novacor system, which is the most advanced.
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From page 245... ...
Permanent total artificial heart devices currently under development will begin initial in vivo experiments within the next three to five years, and some fairly extensive in vivo and in vitro studies should have been completed on all four of the systems being developed under government contact. Five to Ten Years It is reasonable to assume that there will be the same trend in usage of short-term left ventricular assist and total artificial heart devices within the next 5 to 10 years.
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From page 246... ...
~ 989. Chapter As; Current status OT coca application or ventricular assist devices in Japan.
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From page 247... ...
1988. Nine years experience with clinical use of total artificial hearts and cardiac support devices.
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From page 248... ...
1990. Combined Registry for the Clinical Use of Mechanical Ventricular Assist Pumps and the Total Artificial Heart in conjunction with heart transplantation: Fourth official report 1989.
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From page 249... ...
1987. Experimental and clinical experience with the Penn State University total artificial heart.
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From page 250... ...
283-362. Total Artificial Heart.
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