Originally published in Volume 35 Issue 2 of Artificial Organs, 16 February 2011

Dr. William S. Pierce

In 1967, I was a clinical associate in the Cardiac Surgery Branch of the National Heart Institute. I had already been working on mechanical heart development for 7 years. When the news broke that the first successful heart transplant had just been performed, one of my colleagues remarked, “it would have been a great research project but it looks like we won’t need those mechanical hearts.” To the contrary, the greatest stimulus to mechanical heart development has been cardiac transplantation. This highly successful operation shows what can be accomplished when a new heart is substituted for the old. Furthermore, we now know that the need for human donor hearts can never be fulfilled by our current procurement techniques.

Our clinical entry into the field occurred in 1976 with the development and successful use of a paracorporeal pneumatic ventricular assist device (VAD). Originally developed as a support system following cardiac surgery, the most important use has been as a bridge to cardiac transplantation. Currently marketed as the Thoratec PVAD (Thoratec Laboratory Corporation, Pleasanton, CA, USA), the pump has proven highly versatile, serving right, left, or biventricular support, filling from the left atrium or ventricular apex and finding use in patients as small as 17 kg and as large as 100 kg, and for periods of continuous support of over 2 years. The obvious disadvantages of having two (or four) cannulae cross the skin have been overcome by Thoratec, making the “IVAD” an implantable version of the Pierce-Donachy pump (Thoratec Laboratory Corporation). However, the device requires a pneumatic tube to cross the skin and a sizeable but portable pneumatic power unit.

The HeartMate XVE (Thoratec Laboratory Corporation) provided an improvement over our pump. The implantable motor-driven pump traded the pneumatic power line for a thin flexible electrical wire. However, the compliance problem still required a percutaneous air vent. A neat wearable shoulder holster with batteries replaced the pneumatic power unit, considerably increasing patient mobility. Disadvantages included the relatively large size, the limited life of the face cam mechanism, tissue style inlet and outlet valves, and the ever-present percutaneous lines that opened the field to other options.

While continuous flow (axial or centrifugal) pumps have been used industrially for centuries, the concerns regarding blood damage, thrombosis, shaft seal problems, and general lack of a physiological pulse had led blood pump developers to favor valved pulsatile pumps. However, during the past 20 years, interest in continuous flow pumps has burgeoned. Considerably smaller size, elimination of valves and their attendant problems, and the recognition that formed blood elements are “tougher” than previously recognized have resulted in improved options in mechanical circulatory support. The HeartMate II (Thoratec Laboratory Corporation), an implantable axial flow blood pump, is considerably smaller than its pulsatile congeners and is currently achieving excellent success as a bridge device. The unit is electrically powered but needs no vent tube. Thus, the potential for driveline infection, while present, is considerably reduced. Concern centers around a tendency for increased bleeding, possibly from damage to the complex structure of certain plasma proteins such as the Von Willebrand factor. Elimination of the electrical wire would definitely be advantageous and is well within current technical possibilities.


During the past two decades, our group made a major effort to develop a “permanent” or destination device, the LionHeart, with Arrow International (Reading, PA, USA) as a major industrial partner. This electrically powered pulsatile blood pump featured a seam-free blood sac with Björk-Shiley inlet and outlet valves (Thoratec Laboratory Corporation) and activated by a pusher plate. The rotary motor motion was translated to a to-and-fro motion by a long-life industrial roller screw. A sophisticated control system and a rechargeable implanted nickel cadmium battery pack formed a second implantable component. A compact “hot water bottle”-style compliance chamber eliminated the need for a vent tube while energy to charge the implanted battery and the blood pump was transmitted through the intact skin using inductive coupling. About 30 patients in the United States and abroad had the system implanted as a destination device with the longest period of support being about 3 years. Important positive findings include the fact that the motor-roller screw system showed no measurable wear, the compliance chamber was well tolerated and easily managed, and the transcutaneous energy transfer system (TETS) worked well with no skin damage. Problems that occurred were related to an incidence of thromboemboli certainly higher than expected and higher than that seen in our calf implants, what is now old technology implantable battery (nickel cadmium vs. 1/3 smaller lithium ion cells) resulting in two bulky implantable components (pump and battery-control system). Rush to market prevented the use of the lithium ion batteries and also apparently led to surface finishes of certain blood-contacting components that were, in retrospect, unsuitable and may have been responsible for the higher incidence of thromboemboli than seen in the calves. Moreover, the difficulties of a small medical staff managing a complex international trial contributed to some of the problems we encountered.

At the present time, the HeartMate II has limited approval to be used as a destination device and early results are encouraging. With no elastomeric blood sac, the unit should have a very long functioning life. Potential driveline (wire) infection and blood element damage remain concerns.


Naturally, with the increased success of continuous blood pumps, interest has increased regarding the use of two rotary pumps to replace the heart. However, at present, in those patients where removal of the diseased heart is necessary (i.e., aneurysm, ventricular thrombus, septal rupture, etc.), research studies with pulsatile pumps are far ahead. Animal implant studies exceed 1 year and clinical implants over 2 years. The empty pericardial sac provides the space needed for the major component—the two valved blood pumps contained within one housing.

The AbioCor I system developed by the Abiomed engineers (Abiomed, Inc., Danvers, MA, USA) is electrohydraulic with an energized spool-style valve shuttling working fluid to alternately actuate the left and right ventricles. Delicate polymer trileaflet valves are used. Balance of the output of the two ventricles requires a clever shunting system, and no separate compliance chamber is needed. However, a direct measure of left atrial pressure is required. Extensive mock loop durability studies of the pump and separate components have been performed. Calf implant studies have been performed; the protocol calls for an implant duration lasting only a month or two. The intrathoracic components are large and clinical use in about six patients has been limited to critically ill men with a large chest size.

Our group has focused on an electromechanical heart, using the motor-roller screw-pusher plate system employed in the Arrow LionHeart (Arrow International), only a second pusher plate and ventricle have been added. As with the Abiomed heart, the left and right ventricles alternate full to empty ejection. A sophisticated control system regulates the stroke-time division of the pusher plate to balance the output of the two ventricles. Four commercial Björk-Shiley valves are used. Left atrial pressure and arterial pressure analogs are derived indirectly from pump parameters so no pressure transducers are required. An implanted compliance chamber obviates the need for a transcutaneous vent. Power is transmitted across the chest wall using inductive coupling (TETS); accordingly, no transcutaneous wires or tubes are required. Several dozen calf implant studies have been performed with the longest period of continuous pumping just exceeding 1 year.

While spectacular progress is being made with compact VADs, possibly suitable as destination devices, interest and programs in heart replacement have languished. Hopefully, there will be a resurgence of interest and that the goal will be met of having a destination VAD and an electric heart available in our 21st-century operating rooms for use as the need arises.


Dr. William S. Pierce is a cardiac surgeon who served as Head of the Division of Artificial Organs from 1970 until 1997. Along with James H. Donachy and others at Penn State, he developed the widely used Pierce-Donachy pneumatic ventricular assist device, marketed as the Thoratec PVAD. Dr. Pierce is currently Evan Pugh Professor Emeritus, Department of Surgery, College of Medicine, The Pennsylvania State University, Hershey, PA, USA