Landmark Cases

Long sequences of ideas and inventions from many individuals and many disciplines have made bridge to transplantation with a total artificial heart (TAH) possible. In 1953, Gibbon performed the first open heart surgery with the use of an extracorporeal cardiopulmonary bypass and cardiac arrest.¹ In 1957, at the Cleveland Clinic, Akutsu and Kolff successfully implanted a TAH in a dog that survived for 90 minutes.² Using a bovine model in 1963, survival rates of greater than 30 hours were documented. Calves became the experimental model of choice because of better tolerance of cardiopulmonary bypass and less thrombogenicity. These experiments led to testimony in 1963 before Congress that allowed the development of a permanent TAH. In 1964, the National Heart Initiative instituted an order to produce a TAH.

In 1969, Dr. Denton Cooley was the first to implant a TAH, the Liotta TAH, in a human as a bridge to transplant (Table 98-1).³ The patient was supported for 64 hours on the device and then died of pneumonia and sepsis 32 hours after transplantation. The next TAH implantation was in 1981, again by Dr. Cooley.⁴ A 36-year-old man with cardiac failure after coronary artery bypass grafting was implanted with the Akutsu TAH for 53 hours until transplantation. He died 8 days after transplantation, from sepsis. In 1981, Drs. DeVries, Kolff, and Jarvik received U.S. Food and Drug Administration (FDA) approval to permanently implant the Jarvik-7 TAH at the University of Utah. In 1982, their first recipient was Dr. Barney Clark, who lived for 112 days.⁵

Table 98–1 Total Artificial Heart World Experience¹⁸

In 1985, Dr. Jack Copeland of the University of Arizona, attempting to save a patient who had cardiac graft failure, implanted the unapproved Phoenix TAH as a bridge to transplant. The use of an unapproved heart caused controversy, but it resulted in acceptance by the FDA of the one-time use of unapproved devices in true emergencies. This patient died of sepsis after a second transplant. On August 29, 1985, Copeland and his team successfully bridged a young man to transplantation after 9 days of TAH support with a Jarvik-7-100 (with a stroke volume of 100 mL).⁶ This patient survived for more than 5 years, eventually dying of post-transplantation lymphoproliferative disease. This initial success was followed by other successful implants of the 100-mL device before the introduction in 1986 of a smaller device that fit most patients and had a stroke volume of 70 mL, the Jarvik-7-70.

At that time, little was known about prevention of the two major complications of mechanical circulatory support devices, thromboembolism and infection. In 1990, the FDA, realizing that critical follow-up information was not being provided by Symbion, the manufacturer of the Jarvik-7, shut down the investigational device exemption (IDE) study being conducted in the United States. At about the same time, a promising study was released from La Pitié Hospital in Paris⁷ which reported no neurologic complications in 60 consecutive Jarvik-7 patients with the use of a multidrug anticoagulation protocol.

After the closure of all U.S. implantation programs for the Symbion TAH in 1991, the Jarvik-7 was transferred by Symbion to the University Medical Center in Tucson, Arizona. The device was renamed the CardioWest total artificial heart. A new IDE study in five U.S. centers was then approved and initiated in January 1993. The first case was at the University of Arizona. This trial accrued 81 implant patients and 35 controls over a 9-year period. During this time, the manufacturing plant was moved from Vancouver to Tucson. In 2002, a new company, SynCardia Systems, Inc., was founded for the purpose of bringing the IDE study to a conclusion and obtaining approval for commercialization.

In 2004, the CardioWest TAH-t (“t” indicating that the device was approved for temporary use as a bridge to transplantation) was the first and only TAH to be approved by the FDA for use as a bridge to transplant, as reported in the New England Journal of Medicine in 2004.⁸ In international multi-institutional experience, the CardioWest TAH has proved to be an excellent surgical therapy for patients who would otherwise die while awaiting a heart transplant.

Comparison between AbioCor Implantable Replacement Heart and CardioWest TAH-t

The CardioWest TAH-t could be used as a long-term or “permanent” device, but it has not been since the time of DeVries’ four cases and Dr. Semb’s one case in Sweden. The AbioCor (Fig. 98-1) was designed as a permanent artificial heart for patients who are not candidates for any conventional operative therapy or for heart transplantation.

Figure 98–1 The AbioCor heart.

The AbioCor was developed by Abiomed with the Texas Heart Institute. The FDA-approved trial started in 2001. This is a large device, weighing nearly 2 kg and displacing 1500 mL volume. The AbioCor does not require percutaneous lines. Energy is transmitted by radiofrequency transcutaneously to the internal components. The internal components are the thoracic unit, the internal transcutaneous energy transfer, and the internal controller.

After excision of the native ventricles, the AbioCor, a one-piece hydroelectric pulsatile pump, is positioned orthotopically in the chest. The left and right ventricles consist of the energy converter, three motors, and two pumping chambers. The energy converter lies between the two chambers and creates pressure in a unidirectional flow system of a low-viscosity hydraulic fluid in a centrifugal pump. Alternate left and right systoles are produced when the switching valve in the energy converter alternates the direction of the flow between the two chambers. The beat rate is determined by a switching valve, which in turn can produce 8 L/min of fluid at varying rates between 75 to 150 beats per minute. There is a balance chamber between the atria that adjusts the stroke volume to decrease right-sided volumes and prevent overperfusion of the lungs.

The external components consist of four parts: the external transcutaneous energy transfer (TET) coil, batteries, a TET module, and a bedside console. The external TET coil is connected to either a portable TET module or a bedside console. The external TET coil then provides energy to the internal TET coil. The external batteries can be carried in a handbag.

Fourteen of these devices were implanted for a total of 4.5 patient-years, and 534 of the CardioWest TAH-t have been implanted for more than 116 patient-years, and all 44 other types of TAHs have been implanted for a total of 3.5 patient-years.

There was one long-term AbioCor survivor out of hospital. Problems with this device have included its large size, its weight, a high incidence of thromboembolism, limited durability, and extremely high negative pressures in the atria (−40 mm Hg). These negative pressures have caused air embolism at the time of implantation and led to a new abnormal physiology called atrial suck-down, in which the walls of the atria are literally sucked into the atrioventricular (AV) valves, causing obstruction and embolism. The device is approved for humanitarian use by the FDA, but there have been no implants since 2004.⁹

In comparison, the CardioWest TAH-t is currently used in over 30 centers. It is a pneumatic, biventricular, orthotopically placed blood pump. The CardioWest TAH-t replaces the native ventricles with two separate artificial ventricles, left and right. The two artificial ventricles weigh a total of 160 g and displace 400 mL. The Medtronic Hall tilting disc valves, secured to polycarbonate housing, are 27 mm on the inflow side and 25 mm on the outflow side. A four-layer polyurethane diaphragm separates blood and air. If the device fills fully and ejects completely, the stroke volume is 70 mL. The blood flow pathway through each ventricle of 20 cm is about the same as that in the native heart. The inflow distances from native atrium into prosthetic ventricle for the left and right ventricles is less than 0.5 cm, and the Dacron outflow conduits are 3 cm to the aorta and 6 cm to the pulmonary artery. The ventricles are lined with smooth, segmented polyurethane.

Air conduits from the ventricles pass through muscular and subcutaneous tunnels and are attached to 6-foot-long plastic drivelines and an external console. A Dacron covering of the transabdominal wall portion of the drivelines leads to robust healing and adherence to the patient’s tissues, which prevents ascending infections.

The current console is large and mobile within a medical facility. The console, of which there are only 38 in the world, is made up of two pneumatic drives, transport batteries, air tanks, and an alarm and monitoring system. Once the beat rate, “percent systole” (percentage of the cardiac cycle occupied by systole), left and right driving pressures, and vacuum are set manually, it is rare to need to change them. Each artificial ventricle primary driver is set for full ejection of blood. To achieve full ejection, the right ventricle is set to 30 mm Hg greater than the pulmonary artery pressure, and the systemic drive pressure is set to 60 mm Hg higher than the systemic pressure. The console controls are set to fill the ventricles to approximately 50 to 60 mL per beat. This allows the possibility of an increased venous return of 10 to 20 mL (total of 70 mL) in circumstances such as exercise with increased venous return and consequent increase in stroke volume and cardiac output. Thus, the artificial heart, like the native heart, follows the Starling principle (Fig. 98-2).

Figure 98–2 Filling and ejecting cycles of the CardioWest TAH-t.

A 70% to 85% fill of the ventricles coupled with a 100% ejection also allows automatic handling of differences in left and right ventricular fill volumes that occur with, for example, bronchial flow, coughing, and Valsalva maneuvers. It also prevents “over pumping” from the right to the left side, and thus it prevents pulmonary edema, a problem that has been seen with other total artificial hearts. The cardiac output is typically 7 to 8 L/min with mean arterial pressures ranging from 70 to 90 mm Hg and a resulting perfusion pressure of 55 to 80 mm Hg. This is in contrast to the left ventricular assist devices (LVADs), which typically have lower in situ flows that depend on right heart function to deliver blood to the left side and on comparatively long inflow conduits that have inherent resistance as well as the potential to be partially obstructed by ventricular wall.

Two new and much smaller portable consoles exist: the Companion I and Freedom (Fig. 98-3). The Companion I weighs 40 pounds and can be pulled like a suitcase on a modular caddie. It can also be plugged into a hospital console with a bigger screen and a more stable outer structure. The Companion I will also drive biventricular assist devices (BiVADs), univentricular VADs, and an intra-aortic balloon pump. It is scheduled for comparative studies with the large console starting in the third quarter of 2009. The plan is to completely replace all large consoles with the Companion I and to have hundreds of these consoles available worldwide by 2010. The Freedom is the size of a coffee tin and weighs 4 pounds. It contains two drivers, one for continuous use and one for backup. Clinical testing for this very portable driver is scheduled for 2009.

Figure 98–3 CardioWest drivers showing from left to right: the current driver, the Companion I, and the Freedom.