Engineering the Beatless Artificial Heart

The development of the artificial heart can be likened to the invention of the airplane, according to Billy Cohn, MD, a cardiovascular surgeon and device innovator at the Texas Heart Institute. Over the period of centuries, humans sought to develop a flying device with flapping wings that mimicked those of birds and insects. Da Vinci, for instance, created prototypes of flying apparatuses based on biomimicry. The Wright brothers, however, had a different idea that famously proved successful: using fixed wings in conjunction with a propeller system. The propulsion force method for an airplane is unlike any found (on a macro scale) in nature.

Cohn, working with his mentor Bud Frazier, MD, followed a similar approach to develop an artificial heart that constantly and evenly pumps blood. A recipient of the device has no pulse.         

A Pulseless Design

Traditional artificial heart designs were designed to emulate the pumping action of the natural human heart. Frazier himself had worked for decades on pump-based designs that worked to mimic the pulse naturally created by the heart. Speaking at TEDMED, Frazier recounted the experience he had while in medical school at Baylor operating on a young Italian patient in the 1960s. The surgery went well but the patient eventually had a cardiac arrest. In a follow-up emergency procedure, Frazier opened up the patients chest cavity and massaged the patient's heart to keep him alive. It initially worked, but that patient ended up passing away, and the doctors had no other means to prolong the patient's life.

Frazier was intrigued by the experience. If he could keep a temporarily patient alive by physically massaging the heart, why couldn't a pump do the same thing over a longer time frame? A group of researchers set out to develop a pump to do that. The device, which served as a partial artificial heart, was designed to mimic the heart's pulse. Beating roughly once per second, the device began to break down as the cyclic fatigue caused the flexible membranes and internal mechanism to degrade. The device could only last for about a year before breaking. The researchers, however, did confirm the technology's efficacy in prolonging patients' lives.

In 1982, the first heart was implanted. Known as the Jarvik 7, the device imitated the heart's natural lub-dub pumping action. Developed by Robert Jarvik, MD, the device ultimately enabled many patients with a means to survive until they could find a transplant.

Other researchers working in the 1980s, however, decided to follow a different path in developing an artificial heart. Inspired by the Archimedes screw, they developed a continuous flow device that showed promise. Such designs possibly had more potential than the versions that mimicked the heart's pulsing action, which had shown some promise. Patients outfitted with such pulsing devices, however, rarely were able to be discharged from the hospital.

The underlying technology in the pulseless artificial heart has evolved over the years, in part to Cohn and Frazier's efforts. Their most recent innovation was initially developed by linking two ventricular assist devices, which have a bladed rotor that pushes blood continuously--it works more like a propeller than a conventional pump. While those devices had been used to replace a single ventricle, it was unheard of to use the devices to replace the heart.

Cohn and Frazier developed an early prototype that integrated two individual left ventricular assist devices (LVADs). In those studies, the LVAD turbines were connected through the use of medical silicone, dacron cardiovascular patches and hernia mesh.

In a study comprising 70 calves, the double-LVAD devices were successful despite the fact that the calves had no pulse and showed a flatline EKG. A significant number of calves lived for 90 days, surpassing FDA requirements for future clinical trials. In March of 2011, the two replaced the heart of a dying man using the novel device, showing its promise in humans. Further trials also proved successful.

The Latest Pulseless Technology

In 2012, Cohn and Frazier began working Australian mechanical engineer Daniel Timms, PhD, who had designed a device that could replace the heart. Known as the BiVACOR, the titanium device has a propeller-like blood that is suspended within the device by a powerful magnetic field. The propeller is the device's only moving part, which operates without friction, which could make the device impressively long-lasting: potentially lasting more than a decade. By contrast, older pulsatile devices typically have lifetimes of less than three years.

While early prototypes of the device did not prove successful in early animal studies, the BiVACOR did show promise after Frazier and Cohn tested a crude, 3-D printed prototype in a cow. It worked successfully for half of a day. Frazier and Cohn were sold on its potential and helped secure a $2.1-million grant that would enable Timms to leave his native Australis to collaborate with them in Houston.

The latest version of the device, pictured below, calibrates itself 10,000 times per second to the body's blood flow, thus imitating the heart's ability to fine tune blood flow from the left and right ventricle based on various activities. The blade within the device spins 2000 times per minute.

Brian Buntz is the editor-in-chief of MPMN and Qmed. Follow him on Twitter at @brian_buntz.