The Food and Drug Administration approved Medtronic Inc.'s InSync system Tuesday. It's a souped-up pacemaker that provides cardiac resynchronization, making a struggling heart beat more normally by forcing its main pumping chambers to work together.

Cardiologists estimate as many as 650,000 patients could be candidates for the new therapy.

"It's a big breakthrough," said Dr. David DeLurgio, an Emory University cardiologist who helped test the device for Medtronic. "It's not for every heart failure patient, but a proportion could definitely benefit."

"It's not a new heart, but it's an improvement," said FDA medical reviewer Dr. Bram Zuckerman.

Almost 5 million Americans have congestive heart failure. It's not a heart attack or sudden heart stoppage. Instead, a heart weakened by age, damage from a survived heart attack or some other disease gets flabbier as it struggles to push blood out to the rest of the body.

Eventually, patients are pressed even to walk across a room. Fluid seeps into their lungs and blocks breathing. Just half survive five years. When medications fail, a heart transplant is the only option, but many patients are too old to qualify.

Pacemakers are widely used to zap hearts that beat too slowly or irregularly into a normal rhythm. But Medtronic beat two competing companies to the market with a pacemaker that works another way, boosting the beats of weak hearts.

Up to half of heart failure patients have hearts whose main pumping chambers, the left and right ventricles, don't beat together simultaneously and thus sap the heart's power. Medtronic's InSync pacemaker delivers an electrical impulse, from a small pulse generator in the chest down three wires implanted in the heart, that makes the ventricles pump together as a healthy heart's would.

In a study of 579 patients, those using the pacemaker experienced significant improvement, FDA reviewers said.

One standard heart failure test measures how far patients can walk in six minutes and those whose pacemaker was turned on could walk 58 more yards than patients in a comparison group whose pacemaker was turned off. By another measure, 68 percent of pacemaker patients had an improved quality of life compared with 38 percent in the comparison group.

The study lasted just six months and did not measure whether the device helped prolong life. Doctors say for these patients, however, improving quality of life in the short term is a major goal.

InSync is meant only for advanced heart patients who are not helped by the best medical therapy, Zuckerman said, cautioning that it's not a replacement for medication.

Because InSync is different from standard pacemakers, with an additional wire snaked into a different part of the heart, the FDA is requiring Medtronic to give cardiologists special training before they can begin implanting the device.

Minneapolis-based Medtronic is prepared to begin selling the device to trained physicians immediately, and says the operation should cost between $10,000 and $12,000.

On the Net: Food and Drug Administration: http://www.fda.gov

Medtronic: http://www.medtronic.com

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