Artificial heart is latest advance in a story of pioneering medical science
Hal Hodson explains why a good heart is hard to find
Thursday 11 August 2011
The Jarvik-7 looks like two pairs of goggles glued together. It's bulky, beige and doesn't seem like something you would want inside your ribcage.
In the 1980s, anyone receiving the world's first artificial heart was permanently wired to a washing-machine-sized pump with a design that evolved from a milking machine. It weighed as much as a sumo wrestler.
Things have changed. Last week Matthew Green, a husband and father from London, returned home with the modern descendant of the Jarvik-7 beating in his chest. The washing machine is gone, replaced by a 6kg backpack with cables that coil under Green's shirt, running what's known as the Total Artificial Heart.
The technological progression of the artificial heart has been slow. Unlike a scalable, durable silicon chip that can be designed and modelled on a computer, an artificial heart must pass rigorous clinical tests and endure the hostile environment that is the human body. More importantly, the receiving body must survive with a lump of plastic in its chest. In 1628, William Harvey published his best-known work, An Anatomical Exercise on the Motion of the Heart and Blood in Living Beings. "The heart of animals is the foundation of their life, the sovereign of everything within them," Harvey wrote at the start of the book, before going on to dedicate his work to King Charles I.
The book represented the first departure from Galenic physiology, which supposed blood to be distributed through the body by two one-way systems. Harvey proposed that blood circulated around the body, with the heart acting as a pump. "There must be motion, as it were, in a circle," he wrote.
The theory has become fact and a basic block of primary-school biology. Harvey probably never imagined that, close on 400 years after his lifetime, modern science would be able to replace "the foundation of life" with the work of man.
Last week, Green returned to his wife and son one month after a successful operation.
Artificial-heart transplants have not always been such happy events. The first recipient of the Jarvik-7, Barney Clark, spent his final 112 days of borrowed life tethered to a 180kg pump, confused, bleeding and asking to be allowed to die. The second recipient, William Schroeder, survived in a coma for 20 months, the record for survival with a Jarvik-7.
The Total Artificial Heart is also just one segment out of a host of technologies that can help people with heart disease. While the Jarvik-7 was designed as a permanent replacement, its descendent is designated by the US Food and Drug Administration (FDA) as a "bridge-to-transfer" device, allowing a patient to survive until a donor heart can be found. More than 900 people have received the device, which was approved in 2004 after a 10-year clinical study. Today, recipients of a Total Artificial Heart can smile at television cameras with the box that runs their body slung over their shoulder.
Recently, Schroeder's record was beaten after Charles Okeke lived for 864 days with a Total Artificial Heart before receiving a donor heart. Like Green, Okeke was allowed to leave hospital and rejoin his family in Phoenix, Arizona, with a new, portable power source keeping his heart going.
Some hearts aren't broken, just faulty. They can often be fixed by placing what's known as a ventricular assist device (VAD) next to, or in one chamber of, the heart. A VAD takes over for one or both sides of the heart, allowing the patient to survive until a donor heart is found or, sometimes, letting the patient's own heart recover, at which point the VAD is removed.
They are not as extreme as full artificial-heart replacements and benefit from maintaining some of the natural functions of the heart, such as pulse control. The pulse rate of a fully mechanical heart is fixed.
A French heart surgeon called Alain Carpentier is planning to change that. In 2008, Carpentier announced the development of a new generation artificial heart, one that could replace failing organs permanently.
Clinical trials were pencilled in for this year and Carpentier's team is no longer talking to the press, declining to be interviewed until the end of 2011.
The heart promises big improvements: biosynthetic materials will prevent the clotting that has plagued previous artificial hearts; a system of sensors will control heart rate and blood pressure – something current devices are unable to do.
If Carpentier's work is a potential pinnacle of one type of heart technology, bioengineered heart tissue may be another. Mark Post, a tissue engineer from Maastricht University in the Netherlands, says the heart does contain cells that can be used to grow further heart-muscle tissue, but there are huge challenges for the technology. "The tissue engineering of heart muscle is going to be extremely complex," Post says. "It's not only that you need to create the right kind of tissue – that can be done from the cardio-progenitor cells. It also needs to functionally and electrically integrate into the recipient organ, and that will be a major challenge."
It's such a big challenge that, far into the future, Post sees more potential in genetic therapy than engineered tissue for the repair of damaged hearts. He says that when a heart fails, the cells in the wall of the organ do not actually die, but are replaced by fibrous, non-contractile tissue.
"There are other types of fibrous cells in there, fibrocytes, and in theory you could reprogram these cells to become myocytes – contractile cells," he says.
The problem with both of these techniques is that they take time – longer than many patients have, Post says. Artificial hearts will still be needed, if only to keep the patient alive while genetic therapy repairs their original heart.
Twenty-five years ago today, three days after Schroeder died, an article in The New York Times described him and Dr Barney Clark, the first two recipients of an artificial heart, as heroes of medicine.
The article summed up the disappointment of Schroeder's doctors at the quality of his extended life. "They had hoped that today he would be living a nearly normal life, walking about, perhaps with a pack the size of a camera bag slung over his shoulder, carrying the source of his new heart's power," it said.
Although it has taken longer than those doctors would have liked, a quarter of a century later their vision has been realised.
How advanced are other artificial parts?
A good demonstration of the power of protheses is on display in the lower limbs of Oscar Pistorius, the South African sprinter who has just run 400 metres fast enough to qualify for the 2012 Olympics. "Blade Runner", as Pistorius is known, has no legs from mid-calf down, and runs on carbon-fibre blades. His prosthetic legs were ruled to be acceptable for general competition by the IAAF, which said the legs did not give him an unfair advantage.
In medicine, prosthetic hearts have led the way for decades, although other artificial organs are being developed. A medical device firm called MC3 is currently testing a total artificial lung for submission to the Food and Drug Administration in the US. The device is designed to replace carbon dioxide in the blood with oxygen, using the heart's own pumping power.
Artificial livers are in the pipeline, too, although the technical challenges behind creating a whole, mechanical organ mean that most progress has come through growing liver tissue in the lab. Any artificial lung or liver currently in development is designed to be a "bridge to transplant".
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