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Ann Thorac Surg 2001;71:S147-S149
© 2001 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Department of Surgery, University of Louisville, Louisville, Kentucky, USA
b Jewish Hospital Heart and Lung Institute, Louisville, Kentucky, USA
Address reprint requests to Dr Dowling, Division of Cardiothoracic Surgery, University of Louisville, 201 Abraham Flexner Way, Suite 1200, Louisville, KY 40202
e-mail: rddowl01{at}athena.louisville.edu
Presented at the Fifth International Conference on Circulatory Support Devices for Severe Cardiac Failure, New York, NY, Sept 15–17, 2000.
Abstract
Background. The AbioCor implantable replacement heart (IRH) has been developed as an alternative to transplant (ie, destination therapy). We report our experience with the AbioCor IRH in a bovine model at the University of Louisville.
Methods. Male Holstein cows were used (85 to 115 kg). The internal controller, battery, and secondary transcutaneous energy transfer coil were implanted in the right flank. After cardiopulmonary bypass, the thoracic unit was implanted orthotopically. After removal of air and weaning from cardiopulmonary bypass, the AbioCor was connected to internal components and energy transfer through transcutaneous energy transfer coils was achieved.
Results. Nineteen animals underwent implantation of the AbioCor IRH for a proposed 30-day duration. There were 6 deaths, none related to device malfunction. All animals demonstrated normal hemodynamics with normal pressures in the aorta, pulmonary artery, left atrium, and right atrium. There was no significant hemolysis and all animals demonstrated normal end organ function. The internal battery allowed for brief periods of untethered mobility.
Conclusions. The AbioCor IRH has resulted in normal hemodynamics and normal end organ function without evidence of hemolysis in a bovine model.
The incidence of congestive heart failure continues to increase. It has been estimated that approximately 60,000 people in the United States could benefit from cardiac replacement therapy. Heart transplant remains the major surgical alternative for these patients. However, transplantation remains severely limited by the availability of donor organs and by strict medical and financial criteria. Also, despite major advances in the postoperative care of these patients, the half-life survival after transplantation is only about 9 years.
Clearly, there is an acute need for alternative therapies to address the ever-increasing number of patients with refractory end-stage heart failure. Replacement of the native heart with a mechanical device that is totally implantable has been under development for decades and is rapidly approaching clinical trials. In addition to providing an alternative for heart transplant candidates, implantation of a total heart may be an option for the large cohort of patients that are referred for transplant but are not deemed appropriate candidates due to strict medical criteria. We report our experience with the AbioCor (ABIOMED Inc, Danvers, MA) implantable replacement heart (IRH) in a bovine model at the University of Louisville.
Material and methods
Device description
The AbioCor IRH is an electrohydraulically actuated device capable of providing a cardiac output in excess of 8 L/min and has been described previously (Fig 1) [1–4]. The thoracic unit consists of an energy converter and two blood pumps that approximate the shape and volume of the natural heart and is implanted in the pericardial space vacated by the excised natural heart. All blood-contacting surfaces, including the two blood pumps (stroke volume of 60 mL) and the four trileaflet valves (24-mm internal diameter) are fabricated from polyurethane (Angioflex; ABIOMED Inc). This setup results in a continuous blood-contacting surface from the inflow cuff to the outflow graft. The pump domes are reinforced with Stycast epoxy (Emerson Cumming, Woburn, MA). The blood-pump-free membranes are driven hydraulically by a high-efficiency miniature centrifugal pump driven by a brushless direct current motor. This centrifugal pump operates unidirectionally, whereas hydraulic flow reversal is achieved through a two-position porting valve that alternates the direction of the hydraulic fluid flow between the left and right pumping chambers. There is a one-to-one correspondence between blood and hydraulic fluid displacement. An atrial flow-balancing chamber, attached to the left inflow conduit, is located between the left inflow port and left inflow valve and is used to control the left–right blood flow balance [1]. The pump motor impeller and the porting valve are essentially the only moving parts of the energy converter. Textured surface Dacron (E.I. du Pont de Nemours, Wilmington, DE) atrial cuffs and grafts, sutured to the atrial tissues and great vessels, are attached to the inflow port and outflow conduit of the blood pumps by twist-lock connectors. The thoracic unit is connected to an internal controller, battery, and secondary transcutaneous energy transfer (TET) coil. External components of the AbioCor IRH consist of the primary TET coil, batteries, and portable electronics.
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Postoperative hemodynamic monitoring with continuous assessment of pressures in the left and right atrium, pulmonary artery, aorta, and superior vena cava was carried out for all animals. Routine laboratory analyses were performed in all animals, including daily assessment of mixed venous oxygen saturations. Device performance data and hemodynamics are accessible to appropriate personnel by the Internet and therefore can be accessed from remote locations.
Results
Animal experience with the AbioCor device at the University of Louisville began in 1998. Our early efforts were focused at refining and standardizing the operative approach and demonstrating team readiness for clinical trials. Beginning in January 1999, we began a series of experiments in an attempt to demonstrate consistent survival. Since January 1, 1999, we have performed 19 implants with a proposed 30-day study duration. This length of study was decided upon in an effort to provide sufficient data at elective autopsy and to complement longer duration implants that are being performed at the Texas Heart Institute. Twelve of 18 animals (66%) survived to the proposed 30-day study duration, with 1 animal currently on support at the time this article was published. All animals have demonstrated normal atrial pressures and normal systemic and pulmonary artery pressures. The left–right balance control mechanism was successful in all animals in maintaining balance of the systemic and pulmonary circulations, as demonstrated by maintenance of normal right and left atrial filling pressures.
There was 1 death on the third postoperative day that resulted from a transfusion reaction. Blood typing is not possible in cows because there are more than 50 blood group antigens. There was 1 death on postoperative day 5 of unknown etiology without evidence of device malfunction. There were 3 early deaths resulting from anaphylactic shock, most likely traceable to device cleaning methods. One death was due to pulmonary complications.
All animals demonstrated normal neurologic activity and all animals were able to ambulate either in the halls or on a specially designed treadmill. All animals demonstrated normal kidney and liver function (Figs 2 and 3). No evidence of hemolysis was observed in these animals and all animals had adequate tissue oxygenation as demonstrated by daily assessments of mixed venous oxygen with hematocrits in the low 20s to mid-30s.
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The marked increase in the incidence of congestive heart failure combined with the poor prognosis with medical therapy have highlighted the need for an effective therapy to replace the failing heart. Heart transplantation is limited by a severe donor organ shortage and strict medical and financial criteria. Moreover, the number of donor organs has not increased over the last 5 years, which has resulted in an ever-increasing discrepancy between the need for organs and the available supply. Despite advances in xenotransplantation, major hurdles must be addressed, such as immunologic barriers, potential cross-species disease transmission, and ethical issues. Replacement of the heart with a completely implantable, mechanical device has been pursued for decades.
We demonstrated consistent survival with excellent function of the AbioCor IRH in a bovine model. All components demonstrated normal function. The TET system allowed for adequate energy to power the device without any significant thermal injury. The balance control chamber allowed for balance of the systemic and pulmonary systems as evidenced by the ability to maintain normal left- and right-sided filling pressures. The internal batteries allowed for untethered movement and facilitated ambulation of these animals. Current generation batteries are likely to allow for a short period of untethered movement. Future generation batteries are likely to allow for extended periods of untethered mobility. We also demonstrated normal end organ function in these animals without evidence of hemolysis. Currently, device testing on mock circulatory loops and animal implants are ongoing to complete preclinical requirements.
References
This article has been cited by other articles:
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  R. D. Dowling, A. S. Ghaly, and L. A. Gray Jr Creation of a diaphragm patch to facilitate placement of the AbioCor implantable replacement heart Ann. Thorac. Surg., May 1, 2004; 77(5): 1849 - 1850. [Abstract] [Full Text] [PDF]
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 R. D. Dowling, L. A. Gray Jr, S. W. Etoch, H. Laks, D. Marelli, L. Samuels, J. Entwistle, G. Couper, G. J. Vlahakes, and O. H. Frazier Initial experience with the AbioCor Implantable Replacement Heart System J. Thorac. Cardiovasc. Surg., January 1, 2004; 127(1): 131 - 141. [Abstract] [Full Text] [PDF]
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T. J. Myers, K. Robertson, T. Pool, N. Shah, I. Gregoric, and O. H. Frazier Continuous flow pumps and total artificial hearts: management issues Ann. Thorac. Surg., June 1, 2003; 75(90060): S79 - 85. [Abstract] [Full Text] [PDF]
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 E. L. Kukuy, M. C. Oz, and Y. Naka Long-Term Mechanical Circulatory Support Card. Surg. Adult, January 1, 2003; 2(2003): 1491 - 1506. [Full Text]
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