Thursday, May 08, 2008

Tiny Blood Pumps for Failing Hearts

A new heart aid could be implanted without invasive surgery.

By Jocelyn Rice

Pump it up: CircuLite's Synergy, the smallest implantable blood pump in use today, is about the size of a AA battery. Surgeons will eventually implant the pump just below the skin and snake its inflow tube (shown passing under the thumb) into the heart using a catheter. Cracking open the patient’s chest and performing a heart-lung bypass will no longer be necessary. Credit: CircuLite

For a patient with end-stage heart failure, an implantable pump that helps circulate the blood can mean added months or even years of life. Now CircuLite is developing an implantable pump that weighs just one-sixth as much as its smallest predecessor. About the size of a AA battery, it could ultimately be implanted through a catheterization procedure that is far less invasive than the operations used to place today's pumps. It could thus be used to treat patients in earlier stages of heart failure, for whom implantation surgery had previously been too risky.

Invented more than two decades ago, the earliest support pumps--or ventricular assist devices (VADs)--kept patients tethered to a large external console and a blood-thinning machine. A second generation of VADs, still widely in use, has spinning rotors that continuously draw in blood. Third-generation devices are much smaller, using magnetic or hydrostatic forces to float the rotor within the blood. That eliminates friction between the pump's parts, which in earlier generations led to breakdowns and blood clots. But implanting these devices still requires sawing through the breastbone and placing the patient on heart-lung bypass.

CircuLite's pump, called Synergy, uses a combination of magnetic and hydrostatic forces to suspend the rotor. But it differs from a VAD in that it sucks blood from a different chamber of the heart and returns it through a different artery. Because it is designed for patients in an earlier stage of heart failure, whose hearts can still pump a modest amount of blood on their own, the Synergy pump gets by on a smaller, less powerful motor. Unlike implantable VADs, which rest deep inside the chest cavity, the Synergy pump is small enough to be placed near the skin's surface.

"It's a very small, very well engineered device," says Yoshifumi Naka, director of the Mechanical Circulatory Support Program at Columbia University Medical Center.

The device began clinical testing in Europe in June 2007 and has been implanted in nine patients so far. All nine have survived to date, and five have successfully gone on to heart transplants. CircuLite estimates that U.S. clinical trials will begin in early 2009.

The pump itself may sit just beneath the skin, but its inflow tube extends much deeper, into the left atrium of the heart. Currently, in the European studies, the surgeon goes between ribs to place the tube. This "mini-thoracotomy" is faster and safer than the full sternotomy required for most other implantable pumps, but heart-lung bypass is still required.