An
Electric Artificial Heart for Clinical Use WILLIAM S. PIERCE, M.D., GERSON ROSENBERG, PH.D., ALAN J. SNYDER, PH.D., WALTER E. PAE, JR., M.D., JAMES H. DONACHY, and JOHN A. WALDHAUSEN, M.D.
Advances in microelectronics, high-strength magnets, and control system design now make replacement of the heart using an implantable, electrically powered pump feasible. The device described herein is a compact, dual pusher plate unit with valved polyurethane sac-type ventricles positioned at either end. The power unit consists of a small, brushless direct current motor and a motion translator. A microprocessor control system is used to regulate heart beat rate and provide left-right output balance. Bench studies lasting for as long as 1 year have been performed. Heart replacement with the electric heart has been performed in 18 calves since 1984. The longest survivor lived for more than 7 months. Among the causes of termination were component failure, thromboembolic complications, and bleeding. No major problem has been identified that precludes prolonged use of the electric heart. In the future the patient with end-stage heart disease will have an electric artificial heart as one therapeutic option.
provided a new outlook for many patients with end-stage heart disease. However cardiac transplantation is not readily available to all of these patients. The number of donor hearts is limited and thus many patients die while waiting for a donor heart. Other patients have concurrent disease that excludes them from the candidate list, frequently because of the associated need for immunosuppressive therapy. The possibility of heart replacement with a humanmade device was seriously considered by Kolff and Akutsu' in 1958. The first such hearts to be successfully used in experimental animals were pneumatically powered pumps.2 In 1982 DeVries and colleagues3 startled the medical world by electively implanting a pneumatically powered heart in the chest of a 62-year-old man with an end-stage cardiomyopathy. The results encouraged DeVries to implant a similar heart in three other patients, one of whom lived for more than 2 years. However inherent problems with the pneumatic heart (i.e., the need for two tubes to pass through the body wall and the bulky pneumatic power unit) have shifted the focus of the permanent artificial heart to devices that do not require perC
ARDIAC TRANSPLANTATION HAS
Presented at the 1 10th Annual Meeting of the American Surgical Association, Washington, D.C., April 5-8, 1990. Supported in part by USPHS Grant ROI HL 20356, Contract NOI HV 88105 and gifts from the Kleberg Foundation, the Barsumian Trust, and the McKean County Cardiac Committee. Address reprint requests to William S. Pierce, M.D., Department of Surgery, C412, Milton S. Hershey Medical Center, Pennsylvania State University, P.O. Box 850, 500 University Dr., Hershey, PA 17033. Accepted for publication April 12, 1990.
From the Department of Surgery, College of Medicine, the Milton S. Hershey Medical Center, the Pennsylvania State University, Hershey, Pennsylvania
cutaneous tubes and that have smaller external components. This report describes the design and evaluation of an electrically powered artificial heart under development by our group. Materials and Methods The electrically powered heart consists of two pusher plate-activated blood pumps positioned on either side of a motor-motion translator assembly.4'5 Each blood pump is comprised of a very smooth segmented polyurethane sac positioned within a rigid polysulfone housing. Each sac is actuated by a pusher plate. Bjork-Shiley valves (Shiley Laboratories, Inc., Irvine, CA) with Delrin (E.I. DuPont de Nemours Co., Wilmington, DE) discs are secured at the inlet and outlet ports of each pump. The dynamic stroke volume of the pump is 90 ± 5 mL with a maximum output of 12 L per minute. Pusher-plate motion is produced by a brushless DC motor acting through a drum cam (initial version used in 10 calves) or a planetary roller screw (current version used in eight calves). The inlet and outlet ports of the pumps are connected to the respective atria and arteries using filler free silicone rubber-coated Dacron (DuPont) fabric sewing cuffs. The roller-screw electric heart is shown in Figure 1. Electric energy is transmitted to the motor through an inductive coupling technique, which eliminates the need for any tube or wire to cross the skin. The primary (external) coil is energized at 155 kHz using house current or a portable battery pack. Energy is transmitted across the skin to the secondary (subcutaneous) coil with a 70% coupling efficiency.6 The energy is supplied to the motor controller. Information regarding the relative position of the rotor and stator are provided to the controller from Hall effect sensors (Microswitch, Division of Honeywell, Inc., Freeport, IL) on the motor case and a series of ultrahigh-strength magnets attached to the rotor. In the rollerscrew unit, a full stroke (2.5 cm) is provided by 63 revolutions of the nut, first turning in a clockwise and then in a counterclockwise direction. In addition to providing energy for the motor and controller, the secondary coil provides energy to charge an implantable battery capable of supporting pump function for as long as 20 minutes
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FIGS. IA and lB. (A) A crosssection of the electric heart shows the electric motor (rotor and stator), roller screw (shaft and nut), two pusher plates, and the two blood pumps. (B) A photograph of the electric heart. The overall length is 11 cm, height is 10 cm, and the weight is 900 g. The central section of the heart is fabricated of a titanium alloy, while the pump cases are made of transparent
Right pump
Rotor
Guide shaft
polysulfone.
A while the primary coil is temporarily removed or dislodged. An electronic control system is used to balance the output of the right and left ventricles and to ensure adequate cardiac output.7'8 We have extensive experience with the use of automatic control of a pneumatic artificial heart in animals and in humans. With the pneumatic system, the left pump output is increased as arterial pressure decreases to less than its baseline value. The right pump output maintains the left atrial pressure at a normal preset range. This system has been modified for use with the electric heart in which both ventricle beat rates are equal but phase shifted by 180 degrees. Detailed bench studies using the electric heart have shown that the motor torque during left pump systole is related to the arterial pressure, so this value is used in the control scheme. Left atrial pressure is indirectly measured by determining the position at which the left pusher plate contacts the blood sac. Thus both of these key parameters (arterial and left atrial pressure) are indirectly measured without the use of pressure transducers and their attendant problems of temperature sensitivity and temporal drift. The implanted artificial heart contains a relatively fixed gas volume within the motor and pump unit. To achieve effective output balance, the stroke volume of either ventricle must change independently of the other. Because of the fixed volume of gas within the motor space, this change in stroke alters the gas pressure, which can alter the stroke of the opposite ventricle. Accordingly a volumecompensation device or a compliance chamber is a re-
quired component of an artificial heart of this design.9 The compliance chamber is a 10 X 15 X 1 cm segmented polyurethane chamber having a Dacron (DuPont) velour outer cover and is connected to the motor space. In animal implants it is positioned in the right pleural space. Because gasses slowly diffuse across polyurethane membranes, a compliance chamber access port is positioned in the subcutaneous position to allow replenishment of gas lost to diffusion across the polymer. The mechanical heart has undergone extensive bench and mock loop testing. Each ventricle can pump from 6 to 12 L per minute at physiologic inlet and outlet pressures. The control system can handle perturbations in systemic and pulmonary resistances and has proved stable. Power consumption at nominal flow rates of 5 to 10 L per minute, a mean aortic pressure of 90 mmHg, and physiologic left atrial pressures ranged from 6.5 to 17 watts.'0 Overall system efficiency using the wireless energy transmission system ranged from 16. 1% to 20.9%. The longest period of continuous function on the mock circulatory loop has been 1 year. Animal implant studies have been performed using 125kg calves. A right thoracotomy was performed and conventional cardiopulmonary bypass was begun, removing blood from the cavae and pumping blood into the retrograde cannulated right common carotid artery. The heart was removed and atrial and arterial cuffs were doubly sutured with 4-0 polypropylene suture. Because of the mismatch in length-to-width ratio of the pump and chest dimensions, we developed a technique in which the pumps
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mechanical component failure (4), bleeding (2) thromboembolic (1), and undetermined (1). With improvement in the roller-screw motion design heart (smaller size, less weight, improved mechanical reliability), we discontinued development of the cam unit. Since April 1986, eight calves have undergone heart replacement with the roller-screw unit. One animal died in the perioperative period. Seven animals lived from 9 to 170 days (ongoing), with an average survival time of 76 ± 23 SEM days (Fig. 3). Causes of death were electromechanical component failure (3), thromboembolic (2), -and parasitic disease (1).
FIG. 2. This diagram shows the location of the heart in the experimental calf. The heart is positioned in the orthotopic location. The compliance chamber is placed in the right pleural space. Ao, aorta; PA, pulmonary artery; LA, left atrium; RA, right atrium.
are positioned in the calf with the long axis parallel to the sternum (Fig. 2). The quick connects were attached and air was removed from the pump. The heart was slowly energized as cardiopulmonary bypass was discontinued. Protamine was administered after removal of the cannulae. The compliance sac was positioned in the right hemithorax and the chest was closed. (While the wireless energy transmission system has been extensively evaluated on the laboratory bench and in animal studies with electric ventricular assist devices, to date only a hard wired system has been used with heart replacement in the calf.) Each calf was placed in the recovery room in a cage and was extubated when the arterial blood gasses were adequate. After several days monitoring catheters and intravenous cannulas were removed. Each calf was given warfarin sodium to maintain a prothrombin value of 1.5 to 2 times control value. Pump parameters were monitored periodically. The animal was given a normal diet
Discussion Some of the earliest artificial hearts conceived in the 1 960s were designs in which brush-type DC electric motors served as the prime movers.'12"3 Those hearts were generally based on positive-displacement pumps that required an available volume of atrial blood to permit obligatory filling during diastole. If an adequate volume of atrial blood was not available, high suction pressures resulted in disastrous consequences. Brush wear was a potential, but often unrealized, problem. In pneumatic pumps filling is controlled by a gentle vacuum rather and is not obligatory. As a result most artificial heart progress in the 1970s was made with pneumatic devices. The availability of brushless DC motors, a better understanding of control mechanisms, in part, through studies of pneumatically powered artificial hearts in animals, and stable miniature sensors have resulted in an
and water ad libitum. The calf was exercised on a treadmill at prescribed intervals. An animal experiment was terminated if the animal became ill and could not be readily treated or if mechanical failure occurred. A complete necropsy was performed and the artificial heart was removed, disassembled, and thoroughly inspected. Where indicated, required modifications were incorporated in subsequent artificial hearts. Results
Beginning in December 1982, 10 animals underwent implantation of the cam-type artificial hearts." Two animals died within the first week of perioperative problems. The remaining eight calves lived from 9 to 222 days (mean, 50 ± 25 days). The causes of death were electro-
FIG. 3. This calf underwent heart replacement with the roller screw artificial heart. The animal has grown normally and has a good appetite. This photograph was taken 5 months after operation. Hard-wire electric energy transmission is used. The controller has not required adjustment since the first postoperative day. The pressure in the compliance chamber is measured through the subcutaneous access port at 10-day intervals; approximately 30 mL of SF6 gas is added at that time.
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electric heart with the potential for excellent longevity but with no risk of developing dangerously low inlet pressures. Requirements of minimum size and weight have led investigators to evaluate a variety of interesting techniques to convert rotary motor motion to activate a blood pump sac. A Scotch yoke crank, rack and gear, and a unique double-acting cam have been considered, in addition to the drum cam and roller screw described herein.'1'6 Nasar's group'7 has developed a permanent magnet linear oscillating motor for use in an implantable heart. For more than a decade, investigators at the University of Utah have pursued the development of an electrohydraulic heart.'8 In their design the energy converter is positioned between two blood pumps similar in design to the Jarvik 7 artificial heart. The energy converter is a motor-driven miniature high-speed reversing axial-flow pump that pumps a volume of silicone fluid, alternately activating one ventricle and then the other. High suction pressures are prevented by the use of a highly stable piezoelectric transducer that senses the fluid pressure behind each ventricle and alters the heart rate accordingly. Each ventricle has a stroke volume of 100 mL and the maximum output is 10 L per minute. The longest period of circulatory support using this device in the calf has been 1 month. Problems with the device center around the motor bearings and the ability to achieve right-left balance. The animal studies using the heart described herein have used a hard wired system rather than the wireless inductive coupling technique designed for clinical use. This has permitted us to focus on certain elements of the system and to identify problems that had not been identified during bench studies. The flexion life of the elastomeric sac and the maintenance of roller-screw lubrication are ofconcern but do not represent limiting factors. However moisture diffusion across the blood sacs has resulted in failure of the electrical components. We now encapsulate the electric circuit that contains the Hall effect rotor position transducers with a moisture-resistant aliphatic amine-based epoxy elastomer. To eliminate moisture diffusions other researchers have used a low water permeability butyl rubber overcoat of polymeric materials to exclude moisture from electric components. This approach appears to have worked well. The major developmental step that remains in our electric heart program is the use of the wireless energy transmission system and implanted electronics in animals. We have obtained a highly sophisticated miniaturized version of our circuit that will allow us to proceed with the implantation of the control circuitry and the NiCd implantable batteries. These components will permit the use and evaluation of the transcutaneous energy transmission system in the experimental animal. A data transmission scheme, similar to that used with pacemakers,
Ann. Surg. * September 1990
will be used for the bidirectional transfer of data and will be done using a small personal computer attached to the primary coil circuitry. External-to-internal data transfer will be accomplished by frequency-shift keying of the power transmission carrier (±3 kHz). Directions will be transmitted to the controller during start-up. Controller reprogramming rarely has been required during steadystate operation. However a change in both the baseline cardiac output and aortic pressure cardiac output sensitivity curve may be achieved, if indicated. Internal-toexternal data transmission will be based on radio frequency transmission and can be accomplished with the energy transmission system on or off. Available information will include arterial and left atrial pressure, pump parameters, and internal battery voltage.
FIG. 4. This sketch shows the proposed application of the electric artificial heart in a human. The electric heart is positioned in the orthotopic location. Other major components include the transcutaneous energytransfer system (primary and secondary coils), the controller and implantable battery, the compliance chamber positioned in the left pleural space, and the subcutaneous access port.
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FIG. 5. A close relationship will exist between cardiac transplantation and the artificial heart. Younger patients will receive the less-encumbering transplant, while older patients will receive the artificial heart. Many patients who need but do not receive a transplant in our present system, because of ineligibility or donor shortage, will benefit from the mechanical device.
We believe that the electric heart will ultimately assume an important role, along with cardiac transplantation, in the treatment of end-stage heart disease (Fig. 4). A serious shortage of donor organs exists and may become more critical. Donor organs may be reserved for younger patients while the artificial hearts will be used in older patients. Furthermore the complexities of 'bridging' with the use of a temporary mechanical device followed by transplantation can be overcome by using a permanent device for the original operation (Fig. 5).
References 1. Akutsu T, Kolff WJ. Permanent substitute for valves and hearts. Transactions of the American Society for Artificial Internal Organs 1958; 4:230-235. 2. Klain M, Mrava GL, Tajima K, et al. Can we achieve over 100 hours' survival with a total mechanical heart? Transactions of the American Society for Artificial Internal Organs 1971; 17:
437-444.
DISCUSSION
DR. HENRY T. BAHNSON (Pittsburgh, Pennsylvania): One has to applaud the perseverance in the face of so many unanswered problems with this project. It is not far fetched to compare this with the days of development of total cardiopulmonary bypass by Gibbon, something that is now used so widely, or even to the development of balloon augmentation, which now can be implanted percutaneously and even done by cardiologists. In the early days of cardiac surgery every one recognized that total cardiopulmonary bypass was the ideal, but most of us chickened out and used various methods, circulatory arrest with or without hypothermia, the right heart bypass, a la Dewey Dodrill, or the azygous flow principle that was introduced by the Minneapolis group. I admit we have chickened out also at Pittsburgh, and I speak for my younger associates under the leadership of Dr. Hardesty and Dr. Griffith
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3. DeVries WC. The permanent artificial heart. JAMA 1988; 259:849859. 4. Rosenberg G, Snyder AJ, Weiss WJ, et al. A roller screw drive for implantable blood pumps. Transactions of the American Society for Artificial Internal Organs 1982; 28:123. 5. Rosenberg G, Cleary TJ, Snyder AJ, et al. A totally implantable artificial heart design. Transactions of the American Society of Mechanical Engineers 1985; 85-WA/DE-l 1. 6. Weiss WJ, Rosenberg G, Snyder AJ, et al. In vivo performance of a transcutaneous energy transmission system with the Penn State motor-driven ventricular assist device. Transactions of the American Society of Artificial Internal Organs 1989; 35:284288. 7. Landis DL, Pierce WS, Rosenberg G, et al. Long-term in vivo automatic electronic control of the artificial heart. Transactions of the American Society for Artificial Internal Organs 1977; 23: 519-525. 8. Rosenberg G, Snyder AJ, Weiss WJ, et al. An electric motor-driven total artificial heart. IEEE 1982 Frontiers of Engineering in Health Care 1982; 111-1 16. 9. Lee S, Rosenberg G, Donachy JH, et al. The compliance problem: a major obstacle in the development of implantable blood pumps. Artif Organs 1984; 8:82-90. 10. Jurmann MJ, Rosenberg G, Snyder AJ, et al. In-vivo determinants of energy consumption in electric motor-driven artificial hearts. Transactions of the American Society of Artificial Internal Organs 1989; 35:745-747. 11. Rosenberg G, Snyder AJ, Landis DL, et al. An electric motor-driven total artificial heart: seven months survival in the calf. Transactions of the American Society for Artifical Internal Organs 1984; 30:69-74. 12. Kirby CK, Pierce WS, Burney RG, et al. The development of an artificial intrathoracic heart. Surgery 1964; 56:719-725. 13. Akutsu T, Houston CS, Kolff WJ. Artificial heart inside the chest, using small electromotors. Transactions of the American Society for Artificial Internal Organs 1960; 6:299-304. 14. Jarvik RK, Smith LM, Lawson JH, et al. Comparison of pneumatic and electrically powered total artificial hearts in vivo. Transactions of the American Society for Artificial Internal Organs 1978; 24: 593-599. 15. Min BG, Koh CS, No JL, et al. Artificial Heart. United States Patent 4, 718, 903 1988. 16. Takatani S, Takano H, Taenaka Y, et al. Toward a completely implantable total artificial heart. Transactions of the American Society for Artificial Internal Organs 1987; 33:235-239. 17. Yang CH, Nasar SA. A permanent magnet linear oscillatory motor for the total artificial heart. Elec Mach and Power Sys 1988; 15: 381-395. 18. Lioi AP, Orth JL, Crump KR, et al. In vitro development of automatic control for the actively filled electrohydraulic heart. Artif Organs 1988; 12:152-162.
who are either home minding the store or presenting papers at the conflicting meeting of the Heart Transplantation Society. They used the Jarvik, the totally artificial heart, which was the one on your left-hand side in Dr. Pierce's first illustration. This has been used in 19 patients since 1985, only one of them in the last year. Eight of these 19 patients were long-term survivors after transplantation of the heart. This has been our planned use of the total artificial heart, as a bridge to transplantation. In all of these patients infection was a problem, and that was the major cause of death in the group, prompting Dick Simmons to remind us that the best antibiotic is a good blood supply. In contrast to these infection-ridden results with the Jarvik total artificial heart, they have used the Novacor, left ventricular only assist device, in 17 patients. Thirteen of these were subsequently transplanted. All are alive, and infection has not been a major problem. The longest tenure on this machine, (the left ventricular assist device,)
Electric Artificial Heart for Clinical Use WILLIAM S. PIERCE, M.D., GERSON ROSENBERG, PH.D., ALAN J. SNYDER, PH.D., WALTER E. PAE, JR., M.D., JAMES H. DONACHY, and JOHN A. WALDHAUSEN, M.D.
Advances in microelectronics, high-strength magnets, and control system design now make replacement of the heart using an implantable, electrically powered pump feasible. The device described herein is a compact, dual pusher plate unit with valved polyurethane sac-type ventricles positioned at either end. The power unit consists of a small, brushless direct current motor and a motion translator. A microprocessor control system is used to regulate heart beat rate and provide left-right output balance. Bench studies lasting for as long as 1 year have been performed. Heart replacement with the electric heart has been performed in 18 calves since 1984. The longest survivor lived for more than 7 months. Among the causes of termination were component failure, thromboembolic complications, and bleeding. No major problem has been identified that precludes prolonged use of the electric heart. In the future the patient with end-stage heart disease will have an electric artificial heart as one therapeutic option.
provided a new outlook for many patients with end-stage heart disease. However cardiac transplantation is not readily available to all of these patients. The number of donor hearts is limited and thus many patients die while waiting for a donor heart. Other patients have concurrent disease that excludes them from the candidate list, frequently because of the associated need for immunosuppressive therapy. The possibility of heart replacement with a humanmade device was seriously considered by Kolff and Akutsu' in 1958. The first such hearts to be successfully used in experimental animals were pneumatically powered pumps.2 In 1982 DeVries and colleagues3 startled the medical world by electively implanting a pneumatically powered heart in the chest of a 62-year-old man with an end-stage cardiomyopathy. The results encouraged DeVries to implant a similar heart in three other patients, one of whom lived for more than 2 years. However inherent problems with the pneumatic heart (i.e., the need for two tubes to pass through the body wall and the bulky pneumatic power unit) have shifted the focus of the permanent artificial heart to devices that do not require perC
ARDIAC TRANSPLANTATION HAS
Presented at the 1 10th Annual Meeting of the American Surgical Association, Washington, D.C., April 5-8, 1990. Supported in part by USPHS Grant ROI HL 20356, Contract NOI HV 88105 and gifts from the Kleberg Foundation, the Barsumian Trust, and the McKean County Cardiac Committee. Address reprint requests to William S. Pierce, M.D., Department of Surgery, C412, Milton S. Hershey Medical Center, Pennsylvania State University, P.O. Box 850, 500 University Dr., Hershey, PA 17033. Accepted for publication April 12, 1990.
From the Department of Surgery, College of Medicine, the Milton S. Hershey Medical Center, the Pennsylvania State University, Hershey, Pennsylvania
cutaneous tubes and that have smaller external components. This report describes the design and evaluation of an electrically powered artificial heart under development by our group. Materials and Methods The electrically powered heart consists of two pusher plate-activated blood pumps positioned on either side of a motor-motion translator assembly.4'5 Each blood pump is comprised of a very smooth segmented polyurethane sac positioned within a rigid polysulfone housing. Each sac is actuated by a pusher plate. Bjork-Shiley valves (Shiley Laboratories, Inc., Irvine, CA) with Delrin (E.I. DuPont de Nemours Co., Wilmington, DE) discs are secured at the inlet and outlet ports of each pump. The dynamic stroke volume of the pump is 90 ± 5 mL with a maximum output of 12 L per minute. Pusher-plate motion is produced by a brushless DC motor acting through a drum cam (initial version used in 10 calves) or a planetary roller screw (current version used in eight calves). The inlet and outlet ports of the pumps are connected to the respective atria and arteries using filler free silicone rubber-coated Dacron (DuPont) fabric sewing cuffs. The roller-screw electric heart is shown in Figure 1. Electric energy is transmitted to the motor through an inductive coupling technique, which eliminates the need for any tube or wire to cross the skin. The primary (external) coil is energized at 155 kHz using house current or a portable battery pack. Energy is transmitted across the skin to the secondary (subcutaneous) coil with a 70% coupling efficiency.6 The energy is supplied to the motor controller. Information regarding the relative position of the rotor and stator are provided to the controller from Hall effect sensors (Microswitch, Division of Honeywell, Inc., Freeport, IL) on the motor case and a series of ultrahigh-strength magnets attached to the rotor. In the rollerscrew unit, a full stroke (2.5 cm) is provided by 63 revolutions of the nut, first turning in a clockwise and then in a counterclockwise direction. In addition to providing energy for the motor and controller, the secondary coil provides energy to charge an implantable battery capable of supporting pump function for as long as 20 minutes
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FIGS. IA and lB. (A) A crosssection of the electric heart shows the electric motor (rotor and stator), roller screw (shaft and nut), two pusher plates, and the two blood pumps. (B) A photograph of the electric heart. The overall length is 11 cm, height is 10 cm, and the weight is 900 g. The central section of the heart is fabricated of a titanium alloy, while the pump cases are made of transparent
Right pump
Rotor
Guide shaft
polysulfone.
A while the primary coil is temporarily removed or dislodged. An electronic control system is used to balance the output of the right and left ventricles and to ensure adequate cardiac output.7'8 We have extensive experience with the use of automatic control of a pneumatic artificial heart in animals and in humans. With the pneumatic system, the left pump output is increased as arterial pressure decreases to less than its baseline value. The right pump output maintains the left atrial pressure at a normal preset range. This system has been modified for use with the electric heart in which both ventricle beat rates are equal but phase shifted by 180 degrees. Detailed bench studies using the electric heart have shown that the motor torque during left pump systole is related to the arterial pressure, so this value is used in the control scheme. Left atrial pressure is indirectly measured by determining the position at which the left pusher plate contacts the blood sac. Thus both of these key parameters (arterial and left atrial pressure) are indirectly measured without the use of pressure transducers and their attendant problems of temperature sensitivity and temporal drift. The implanted artificial heart contains a relatively fixed gas volume within the motor and pump unit. To achieve effective output balance, the stroke volume of either ventricle must change independently of the other. Because of the fixed volume of gas within the motor space, this change in stroke alters the gas pressure, which can alter the stroke of the opposite ventricle. Accordingly a volumecompensation device or a compliance chamber is a re-
quired component of an artificial heart of this design.9 The compliance chamber is a 10 X 15 X 1 cm segmented polyurethane chamber having a Dacron (DuPont) velour outer cover and is connected to the motor space. In animal implants it is positioned in the right pleural space. Because gasses slowly diffuse across polyurethane membranes, a compliance chamber access port is positioned in the subcutaneous position to allow replenishment of gas lost to diffusion across the polymer. The mechanical heart has undergone extensive bench and mock loop testing. Each ventricle can pump from 6 to 12 L per minute at physiologic inlet and outlet pressures. The control system can handle perturbations in systemic and pulmonary resistances and has proved stable. Power consumption at nominal flow rates of 5 to 10 L per minute, a mean aortic pressure of 90 mmHg, and physiologic left atrial pressures ranged from 6.5 to 17 watts.'0 Overall system efficiency using the wireless energy transmission system ranged from 16. 1% to 20.9%. The longest period of continuous function on the mock circulatory loop has been 1 year. Animal implant studies have been performed using 125kg calves. A right thoracotomy was performed and conventional cardiopulmonary bypass was begun, removing blood from the cavae and pumping blood into the retrograde cannulated right common carotid artery. The heart was removed and atrial and arterial cuffs were doubly sutured with 4-0 polypropylene suture. Because of the mismatch in length-to-width ratio of the pump and chest dimensions, we developed a technique in which the pumps
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mechanical component failure (4), bleeding (2) thromboembolic (1), and undetermined (1). With improvement in the roller-screw motion design heart (smaller size, less weight, improved mechanical reliability), we discontinued development of the cam unit. Since April 1986, eight calves have undergone heart replacement with the roller-screw unit. One animal died in the perioperative period. Seven animals lived from 9 to 170 days (ongoing), with an average survival time of 76 ± 23 SEM days (Fig. 3). Causes of death were electromechanical component failure (3), thromboembolic (2), -and parasitic disease (1).
FIG. 2. This diagram shows the location of the heart in the experimental calf. The heart is positioned in the orthotopic location. The compliance chamber is placed in the right pleural space. Ao, aorta; PA, pulmonary artery; LA, left atrium; RA, right atrium.
are positioned in the calf with the long axis parallel to the sternum (Fig. 2). The quick connects were attached and air was removed from the pump. The heart was slowly energized as cardiopulmonary bypass was discontinued. Protamine was administered after removal of the cannulae. The compliance sac was positioned in the right hemithorax and the chest was closed. (While the wireless energy transmission system has been extensively evaluated on the laboratory bench and in animal studies with electric ventricular assist devices, to date only a hard wired system has been used with heart replacement in the calf.) Each calf was placed in the recovery room in a cage and was extubated when the arterial blood gasses were adequate. After several days monitoring catheters and intravenous cannulas were removed. Each calf was given warfarin sodium to maintain a prothrombin value of 1.5 to 2 times control value. Pump parameters were monitored periodically. The animal was given a normal diet
Discussion Some of the earliest artificial hearts conceived in the 1 960s were designs in which brush-type DC electric motors served as the prime movers.'12"3 Those hearts were generally based on positive-displacement pumps that required an available volume of atrial blood to permit obligatory filling during diastole. If an adequate volume of atrial blood was not available, high suction pressures resulted in disastrous consequences. Brush wear was a potential, but often unrealized, problem. In pneumatic pumps filling is controlled by a gentle vacuum rather and is not obligatory. As a result most artificial heart progress in the 1970s was made with pneumatic devices. The availability of brushless DC motors, a better understanding of control mechanisms, in part, through studies of pneumatically powered artificial hearts in animals, and stable miniature sensors have resulted in an
and water ad libitum. The calf was exercised on a treadmill at prescribed intervals. An animal experiment was terminated if the animal became ill and could not be readily treated or if mechanical failure occurred. A complete necropsy was performed and the artificial heart was removed, disassembled, and thoroughly inspected. Where indicated, required modifications were incorporated in subsequent artificial hearts. Results
Beginning in December 1982, 10 animals underwent implantation of the cam-type artificial hearts." Two animals died within the first week of perioperative problems. The remaining eight calves lived from 9 to 222 days (mean, 50 ± 25 days). The causes of death were electro-
FIG. 3. This calf underwent heart replacement with the roller screw artificial heart. The animal has grown normally and has a good appetite. This photograph was taken 5 months after operation. Hard-wire electric energy transmission is used. The controller has not required adjustment since the first postoperative day. The pressure in the compliance chamber is measured through the subcutaneous access port at 10-day intervals; approximately 30 mL of SF6 gas is added at that time.
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electric heart with the potential for excellent longevity but with no risk of developing dangerously low inlet pressures. Requirements of minimum size and weight have led investigators to evaluate a variety of interesting techniques to convert rotary motor motion to activate a blood pump sac. A Scotch yoke crank, rack and gear, and a unique double-acting cam have been considered, in addition to the drum cam and roller screw described herein.'1'6 Nasar's group'7 has developed a permanent magnet linear oscillating motor for use in an implantable heart. For more than a decade, investigators at the University of Utah have pursued the development of an electrohydraulic heart.'8 In their design the energy converter is positioned between two blood pumps similar in design to the Jarvik 7 artificial heart. The energy converter is a motor-driven miniature high-speed reversing axial-flow pump that pumps a volume of silicone fluid, alternately activating one ventricle and then the other. High suction pressures are prevented by the use of a highly stable piezoelectric transducer that senses the fluid pressure behind each ventricle and alters the heart rate accordingly. Each ventricle has a stroke volume of 100 mL and the maximum output is 10 L per minute. The longest period of circulatory support using this device in the calf has been 1 month. Problems with the device center around the motor bearings and the ability to achieve right-left balance. The animal studies using the heart described herein have used a hard wired system rather than the wireless inductive coupling technique designed for clinical use. This has permitted us to focus on certain elements of the system and to identify problems that had not been identified during bench studies. The flexion life of the elastomeric sac and the maintenance of roller-screw lubrication are ofconcern but do not represent limiting factors. However moisture diffusion across the blood sacs has resulted in failure of the electrical components. We now encapsulate the electric circuit that contains the Hall effect rotor position transducers with a moisture-resistant aliphatic amine-based epoxy elastomer. To eliminate moisture diffusions other researchers have used a low water permeability butyl rubber overcoat of polymeric materials to exclude moisture from electric components. This approach appears to have worked well. The major developmental step that remains in our electric heart program is the use of the wireless energy transmission system and implanted electronics in animals. We have obtained a highly sophisticated miniaturized version of our circuit that will allow us to proceed with the implantation of the control circuitry and the NiCd implantable batteries. These components will permit the use and evaluation of the transcutaneous energy transmission system in the experimental animal. A data transmission scheme, similar to that used with pacemakers,
Ann. Surg. * September 1990
will be used for the bidirectional transfer of data and will be done using a small personal computer attached to the primary coil circuitry. External-to-internal data transfer will be accomplished by frequency-shift keying of the power transmission carrier (±3 kHz). Directions will be transmitted to the controller during start-up. Controller reprogramming rarely has been required during steadystate operation. However a change in both the baseline cardiac output and aortic pressure cardiac output sensitivity curve may be achieved, if indicated. Internal-toexternal data transmission will be based on radio frequency transmission and can be accomplished with the energy transmission system on or off. Available information will include arterial and left atrial pressure, pump parameters, and internal battery voltage.
FIG. 4. This sketch shows the proposed application of the electric artificial heart in a human. The electric heart is positioned in the orthotopic location. Other major components include the transcutaneous energytransfer system (primary and secondary coils), the controller and implantable battery, the compliance chamber positioned in the left pleural space, and the subcutaneous access port.
CLINICAL ELECTRIC ARTIFICIAL HEART
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FIG. 5. A close relationship will exist between cardiac transplantation and the artificial heart. Younger patients will receive the less-encumbering transplant, while older patients will receive the artificial heart. Many patients who need but do not receive a transplant in our present system, because of ineligibility or donor shortage, will benefit from the mechanical device.
We believe that the electric heart will ultimately assume an important role, along with cardiac transplantation, in the treatment of end-stage heart disease (Fig. 4). A serious shortage of donor organs exists and may become more critical. Donor organs may be reserved for younger patients while the artificial hearts will be used in older patients. Furthermore the complexities of 'bridging' with the use of a temporary mechanical device followed by transplantation can be overcome by using a permanent device for the original operation (Fig. 5).
References 1. Akutsu T, Kolff WJ. Permanent substitute for valves and hearts. Transactions of the American Society for Artificial Internal Organs 1958; 4:230-235. 2. Klain M, Mrava GL, Tajima K, et al. Can we achieve over 100 hours' survival with a total mechanical heart? Transactions of the American Society for Artificial Internal Organs 1971; 17:
437-444.
DISCUSSION
DR. HENRY T. BAHNSON (Pittsburgh, Pennsylvania): One has to applaud the perseverance in the face of so many unanswered problems with this project. It is not far fetched to compare this with the days of development of total cardiopulmonary bypass by Gibbon, something that is now used so widely, or even to the development of balloon augmentation, which now can be implanted percutaneously and even done by cardiologists. In the early days of cardiac surgery every one recognized that total cardiopulmonary bypass was the ideal, but most of us chickened out and used various methods, circulatory arrest with or without hypothermia, the right heart bypass, a la Dewey Dodrill, or the azygous flow principle that was introduced by the Minneapolis group. I admit we have chickened out also at Pittsburgh, and I speak for my younger associates under the leadership of Dr. Hardesty and Dr. Griffith
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3. DeVries WC. The permanent artificial heart. JAMA 1988; 259:849859. 4. Rosenberg G, Snyder AJ, Weiss WJ, et al. A roller screw drive for implantable blood pumps. Transactions of the American Society for Artificial Internal Organs 1982; 28:123. 5. Rosenberg G, Cleary TJ, Snyder AJ, et al. A totally implantable artificial heart design. Transactions of the American Society of Mechanical Engineers 1985; 85-WA/DE-l 1. 6. Weiss WJ, Rosenberg G, Snyder AJ, et al. In vivo performance of a transcutaneous energy transmission system with the Penn State motor-driven ventricular assist device. Transactions of the American Society of Artificial Internal Organs 1989; 35:284288. 7. Landis DL, Pierce WS, Rosenberg G, et al. Long-term in vivo automatic electronic control of the artificial heart. Transactions of the American Society for Artificial Internal Organs 1977; 23: 519-525. 8. Rosenberg G, Snyder AJ, Weiss WJ, et al. An electric motor-driven total artificial heart. IEEE 1982 Frontiers of Engineering in Health Care 1982; 111-1 16. 9. Lee S, Rosenberg G, Donachy JH, et al. The compliance problem: a major obstacle in the development of implantable blood pumps. Artif Organs 1984; 8:82-90. 10. Jurmann MJ, Rosenberg G, Snyder AJ, et al. In-vivo determinants of energy consumption in electric motor-driven artificial hearts. Transactions of the American Society of Artificial Internal Organs 1989; 35:745-747. 11. Rosenberg G, Snyder AJ, Landis DL, et al. An electric motor-driven total artificial heart: seven months survival in the calf. Transactions of the American Society for Artifical Internal Organs 1984; 30:69-74. 12. Kirby CK, Pierce WS, Burney RG, et al. The development of an artificial intrathoracic heart. Surgery 1964; 56:719-725. 13. Akutsu T, Houston CS, Kolff WJ. Artificial heart inside the chest, using small electromotors. Transactions of the American Society for Artificial Internal Organs 1960; 6:299-304. 14. Jarvik RK, Smith LM, Lawson JH, et al. Comparison of pneumatic and electrically powered total artificial hearts in vivo. Transactions of the American Society for Artificial Internal Organs 1978; 24: 593-599. 15. Min BG, Koh CS, No JL, et al. Artificial Heart. United States Patent 4, 718, 903 1988. 16. Takatani S, Takano H, Taenaka Y, et al. Toward a completely implantable total artificial heart. Transactions of the American Society for Artificial Internal Organs 1987; 33:235-239. 17. Yang CH, Nasar SA. A permanent magnet linear oscillatory motor for the total artificial heart. Elec Mach and Power Sys 1988; 15: 381-395. 18. Lioi AP, Orth JL, Crump KR, et al. In vitro development of automatic control for the actively filled electrohydraulic heart. Artif Organs 1988; 12:152-162.
who are either home minding the store or presenting papers at the conflicting meeting of the Heart Transplantation Society. They used the Jarvik, the totally artificial heart, which was the one on your left-hand side in Dr. Pierce's first illustration. This has been used in 19 patients since 1985, only one of them in the last year. Eight of these 19 patients were long-term survivors after transplantation of the heart. This has been our planned use of the total artificial heart, as a bridge to transplantation. In all of these patients infection was a problem, and that was the major cause of death in the group, prompting Dick Simmons to remind us that the best antibiotic is a good blood supply. In contrast to these infection-ridden results with the Jarvik total artificial heart, they have used the Novacor, left ventricular only assist device, in 17 patients. Thirteen of these were subsequently transplanted. All are alive, and infection has not been a major problem. The longest tenure on this machine, (the left ventricular assist device,)
