Babbage | Technology monitor

A wireless heart

Better artificial pumps may help those who cannot get transplants

By The Economist online

DICK CHENEY has no heartbeat. That might sound like the punch line to a political joke but for the former American vice-president it is deadly serious. Mr Cheney is one of thousands of people around the world who have a left ventricular assist device (LVAD) implanted in their hearts.

LVADs—mechanical pumps that take the stress away from a failing heart by moving blood smoothly around the body without generating a pulse—have become smaller and more reliable over the years since their introduction in the 1994. They were originally designed as a stopgap, to keep someone alive for a few extra months, so that a suitable transplantable heart could be found. Improvements in the technology, and a lack of donor organs, however, mean they are being used more and more as treatments in their own right.

One area in which they have not improved, though, is their power supply. The pump requires an electric cable, called a driveline, that runs through the abdominal wall to a battery pack in a harness. This device, which must be worn all the time, hampers mobility, makes it awkward for the wearer to shower (and impossible to swim) and means he cannot drive because even a minor shunt that dislodged the driveline could kill him. Most importantly, though, it is a constant source of infection. With most medical implants, such as pacemakers and hip replacements, the risk of infection decreases over time. But not only does the driveline continually collect bugs from the outside world, the LVAD then also introduces them directly into the bloodstream, allowing them to spread quickly. Because of that, the driveline must be redressed every day using sterile gloves and gauze. And even so, virtually everyone fitted with an LVAD experiences an infection every 12 to 18 months. Many such infections are serious. Some are fatal.

Joshua Smith, an engineer at the University of Washington, and Pramod Bonde, a heart surgeon at the University of Pittsburgh, hope to change that. (See our video about Joshua Smith's work in wireless power.) Between them they have developed the world's first wireless-powered, driveline-free heart pump. The device's existence will be announced formally at the American Association for Thoracic Surgery's annual meeting in May.

The Free-Range Resonant Electrical Energy Delivery System, or FREE-D, as Dr Smith calls it, is powered by induction. Specifically, it exploits a phenomenon called resonant coupling, in which metal coils that resonate at the same electrical frequency can exchange energy particularly efficiently. The process transfers the power using a tuned magnetic field, which is considered less hazardous to human health than the radio waves (or even lasers) that other wireless power systems rely on. Dr Smith's version has a transmitter coil 26cm in diameter, which that can beam up to 15 watts of power to a receiver coil that is just 4.3cm across. The transmitter coil can thus be worn in a vest that also holds a battery pack while the receiver tucks nicely into the patient's chest.

Dr Smith's design is able to compensate for changes in the angle or position of the coils, allowing a user to move around freely. He thus envisages beds with built-in transmitter coils, so that people can sleep without a vest on, and even entire hospital rooms (or houses) that have coils hidden in the walls and ceilings.

Such improvements cannot come a moment too soon. America's National Heart, Lung and Blood Institute estimates that more than 50,000 Americans a year need a heart transplant or an LVAD. In fact, fewer than 2,500 heart transplants are performed in the country every year and the number of LVAD implants is even smaller. As the supply of donor hearts is unlikely to increase, wireless LVADs may become many people's best hope for survival.

Dr Bonde and Dr Smith warn against expecting wireless heart pumps to be available in the immediate future. Technical challenges remain, including integrating a leakproof backup battery into the mix and miniaturising the FREE-D's control electronics. And even when those problems are solved, the device will still have to undergo further trials before it can be licensed for sale.

If the history of medical research teaches anything, though, it is that conditions which affect rich, powerful men like Dick Cheney have little difficulty attracting the money needed to develop new treatments. In just a few years, then, the world could be full of thousands more healthy, active ex-politicians without a heartbeat. Insert your own punch line here.

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