Victor Poirier

Design features, developmental status, and experimental results with the Heartmate III centrifugal left ventricular assist system with a magnetically levitated rotor.

A long-term left ventricular assist system for permanent use in advanced heart failure is being developed on the basis of a compact centrifugal pump with a magnetically levitated rotor and single-fault–tolerant electronics. Key features include its “bearingless” (magnetic levitation) design, textured surfaces similar to the HeartMate XVE left ventricular assist device (LVAD) to reduce anticoagulation requirements and thromboembolism, a sensorless flow estimator, and an induced pulse mode for achieving an increased level of pulsatility with continuous flow assistance. In vitro design verification testing is underway. Preclinical testing has been performed in calves demonstrating good in vivo performance at an average flow rate of 6 L/min (maximum: >11 L/min) and normal end-organ function and host response. Induced pulse mode demonstrated the ability to produce a physiological pulse pressure in vivo. Thirteen LVADs have achieved between 16 to 40 months of long-term in vitro reliability testing and will be continued until failure. Both percutaneous and fully implanted systems are in development, with a modular connection for upgrading without replacing the LVAD.

HeartMate III: pump design for a centrifugal LVAD with a magnetically levitated rotor.

A long-term, compact left ventricular assist device (LVAD), the HeartMate III, has been designed and fabricated, featuring a centrifugal pump with a magnetically levitated rotor. The pump has been optimized by in vitro testing to achieve a design point of 7 L/min against 135 mm Hg at high hydrodynamic efficiency (30%) and to be capable of up to 10 L/min under such a load. Furthermore, the pump has demonstrated no mechanical failures, low hemolysis (4–10 mg/dl plasma free Hb), and low thrombogenicity during six (40, 27, 59, 42, 27, and 49-day) in vivo bovine studies.

The Quest for a Solution

As described in the Design News Engineering Achievement Award, I was considered an engineer for the long haul as I began working on artificial heart technology in 1966 while employed at Thermo Electron Corporation (Waltham, MA, USA). This company was one of six companies that received funding contracts in 1966 from the National Heart, Lung, and Blood Institute (NHLBI) to develop artificial heart technology. Our concept at that time was to develop a nuclear-powered artificial heart capable of supporting the entire circulation in man. For animal trials, we chose a 50-watt plutonium 238 fuel capsule as the energy source. The heat generated by the fuel capsule was used to boil water to make steam, which ran a miniature steam engine. The rotary power that was produced by the engine was then used to drive a hydraulic pump, which activated the blood pump. Unfortunately, this system was not very efficient and required a significant amount of waste heat to be disposed of. To accomplish this, waste heat was transferred through a heat exchanger into the blood stream. The animal’s response to the increased thermal load was a slight increase in the animal’s core temperature as well as a slight increase in the respiration rate. Thermal and radiation experiments were conducted in primates, which established that up to 0.7 watts per kilogram could be used without ill effects. Only minor lymphocyte abnormalities were observed following the animals through three generations.Work on the development of a nuclear-powered system was eventually terminated to concentrate on electrically powered systems that were considered simpler and without the hazards of nuclear radiation. Unfortunately, battery technology was not yet at the level of sophistication in the late 1960s and early 1970s that we required for artificial heart systems. The rechargeable systems lacked the power densities and reliabilities that we needed. In the 1960s, very little was known about implantable power sources, biomaterials, toxicity, the blood/ biomaterial interface, and the mating of mechanical systems to the biological systems of man and animals. We pioneered the development of textured surfaces for both rigid and flexible surfaces and investigated a large variety of power sources. We designed and developed over 15 different blood pump configurations using a variety of different mechanical and tissue valves as well as evaluated various biomaterials and conduit designs. Before we could undertake clinical trials in man, we had to develop and test a wide variety of materials, bonding processes, protective coatings, methods of attachment to the biological system as well as evaluate the response of the biological system to the foreign materials that we were using. As there were very few acceptable biomaterials at that time, we were forced to undertake material development to meet our specific needs and to demonstrate that these materials were not toxic to the biological system and remained stable for an extended duration of time. The body is a hostile doi:10.1111/j.1525-1594.2011.01313.x Artificial Organs 35(8):749–752, Wiley Periodicals, Inc.