The device, called a C-Pulse, has yet to prove its mettle. But the heart specialists who invented it hope it will one day be used to treat thousands of patients who suffer so-called "moderate" heart failure. These people are not ill enough for a heart transplant or an artificial heart, with the risks they bring. But they may suffer symptoms such as extreme tiredness, and struggle to walk short distances even with the best drug therapy.
The C-Pulse comprises an inflatable polyurethane balloon pressed against the aorta, the main artery from the heart. The balloon is kept in place by a polyester wrap stitched around the vessel, and together they form a cuff that follows the contours of the aorta. "It's engineered to fit your body, not to look like it came out of your washing machine," says William Peters, one of the two inventors, who is based at the Auckland City Hospital, New Zealand, and the company Sunshine Heart of Sydney, Australia.
The balloon reinforces the pumping action of a weakened heart (see Diagram). Each beat moves blood from the left ventricle into the aorta. Around 20 milliseconds after each beat, the balloon inflates, squeezing the aorta and propelling the blood with greater force down the artery and around the body. The short delay gives the heart valve time to close, ensuring the blood is not pushed back into the ventricle.
The balloon then deflates, relieving the back pressure on the heart, so it can more easily eject blood with its next beat, after which the balloon once more inflates, completing its cycle.
Surgically implanted leads on the surface of the heart monitor its activity and transmit the data to a processor carried by the patient in a pack. The processor instructs the balloon to inflate and deflate, using air from an external pump. The device is powered by a rechargeable battery or may be plugged into the mains when the patient is not moving about.
"It's a clever technology. The question is, will it provide enough benefit to justify going to the trouble and risk of opening up the chest of a patient," says John Woodard, chief scientific officer of Sydney-based company Ventracor, which is developing a heart pump to treat more seriously ill patients (New Scientist, 31 July 2004, p 19). At the American Heart Association meeting in New Orleans in November 2004, the other inventor behind the C-Pulse, cardiothoracic surgeon Paget Milsom of Auckland City Hospital, reported the results of operating the device for 20 minutes in six volunteers who were undergoing coronary bypass surgery. With the C-Pulse pumping, blood flow in the left coronary artery, which runs from the aorta to the heart, increased by 67 per cent. A study in six pigs showed a similar increase.
But until a 56-year-old man was fitted with the device on 4 May, its ability to improve the health of a patient with heart failure had never been tested. The Auckland team has approval to operate on five more patients with moderate heart failure as part of a pilot study. After three and six months, they will use standard questionnaires to assess these patients' quality of life. They will also use ultrasound to monitor the performance of the heart.
About 5 million people live with heart failure in the US, but only a few thousand hearts are available for transplant. "In heart failure, the heart is still doing something. It just needs to be augmented, not replaced," says Peters.
Currently, two main types of artificial heart pump are available: a mechanical heart that is surgically implanted in place of the patient's own, or the more common "assist device", a pump that is connected into the aorta alongside the heart (New Scientist, 30 October 2004, p 28). Both must be plumbed directly into the bloodstream, which requires complicated surgery and brings with it a significant risk of complications such as blood clots.
"Ventricular assist devices are very effective," says Christopher Bowles, an artificial heart specialist at Harefield Hospital in London. But patients who receive them have a 25 to 30 per cent chance of dying during or shortly after the operation, so they are only offered to very sick people whose chances of survival without an operation are even worse, he says. Bowles and his colleague Asghar Khaghani, also at Harefield Hospital, are in the early stages of developing a device similar to the C-Pulse called the AK-Pulsator.
In theory, says Bowles, such devices should be far less dangerous than the heart pumps now available, because they do not come into contact with blood. "The biggest risk will be if we get an infection on the cuff," Peters says. When the devices were implanted into 26 sheep for between one and 10 months, cuffs became infected in seven of the sheep, two seriously. The risk may be lower in people, because of better surgical hygiene and close monitoring so that infections can be treated quickly.
Early intervention also increases the likelihood that the heart may recover enough to allow the C-Pulse to be disconnected- a very difficult thing to do with conventional heart pumps. "At the moment, it's conjecture. But if it can be done, it would be absolutely wonderful," Bowles says.
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THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 21 MAY 2005
Written by Rachel Nowak, Melbourne