About six years ago Charline Calderon was stricken with a cluster of unusual symptoms that made her feel as if she were about to die.

"Sometimes my heart would start fluttering, sometimes for just a few seconds and then it would get more intense," the retired directory assistance operator said. "I felt faint and weak; I had a very strong sensation of death."

Her doctor's diagnosis: atrial fibrillation, an often rapid and irregular heart rate that dramatically escalates the risk for stroke. Atrial fibrillation is a growing public health concern expected to worsen as the population inexorably ages.

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Calderon, 63, like virtually all of the 2.7 million people who are diagnosed with the condition annually, was prescribed a blood thinner, a medication that alleviates the stroke risk by changing the chemistry of the blood.

But there is a dicey trade-off when taking a blood thinner -- the risk of stroke declines while chances of drug-induced bleeding increase for some patients. Coumadin, the drug Calderon's doctor prescribed, caused such serious gastrointestinal bleeding that she was hospitalized three times last year alone.

Last week, Calderon became one of four pioneering patients on Long Island when doctors at North Shore University Hospital in Manhasset implanted into her heart a device about the size of a quarter and the shape of a parachute. It mechanically prevents atrial fibrillation and eliminates the need for a blood thinner. The device, which inhibits clotting, was approved in April by the U.S. Food and Drug Administration.

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The tiny mechanism is the brainchild of medical device makers at Boston Scientific and is expected to replace the need for blood thinners in high-risk patients. The implant is called the Watchman and is inserted into the heart through a vein in the leg in a one-time, minimally invasive procedure.

Its emergence marks yet another chapter in the growing catalog of devices that eliminate serious cardiovascular risks through diminutive, permanently implanted machines. Last year, two different manufacturers produced miniature pacemakers, each without wires.

"As an electrophysiologist, atrial fibrillation is probably one of the most common conditions that I see," said Dr. Stuart Beldner of North Shore, one of Calderon's doctors. "I have probably offered it [the device] to close to 30 patients."

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Beldner said some patients aren't eager to give up blood thinners despite having to be extraordinarily careful while on the drugs.

"They tend to walk away from new technology," Beldner said. "I have spoken to some people and they have told me: 'When you've done 500 of them, then I will have it done.' "

While taking a blood thinner patients must limit green leafy vegetables because the vitamin K content can elevate the potential for blood clots. They also must guard against falls, nicks and other daily causes of accidents to prevent bleeding.

Beldner said one of his atrial fibrillation patients slipped on an icy surface during winter and wound up in the hospital for six months because of injuries from the fall and excessive bleeding, the result of blood-thinning medication.

In atrial fibrillation the heart quivers, explained Dr. Apoor Patel, also an electrophysiologist at North Shore University Hospital in Manhasset. And because of the loss of a healthy lub-dub, lub-dub of a robust heart beat, blood is not pumped at an appropriate velocity.

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The organ's two upper chambers are out of sync with its two ventricles, or lower chambers. When the heart isn't doing its job as a pump, blood can pool and form the clots that raise the risk of having a stroke, he said.

People at highest risk, Patel said, are in their 50s and older. Calderon was in her mid-50s when the condition emerged.

Dr. Vivek Reddy of Mount Sinai Hospital in Manhattan, who led clinical trials of the device and implanted the first Watchman on the Eastern Seaboard, said blood-thinning medications are very effective in reducing the stroke risk.

"However, many of our patients cannot, or will not, tolerate these medications," said Reddy, director of arrhythmia services.

The Watchman, Reddy said, has a narrow approval profile and remains a device for those at highest risk on blood thinning drugs.

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Calderon, who lives in Jamaica, Queens, is pleased she underwent the procedure.

"I am not having any side effects," she said Friday. "I went in on Monday morning and went home Tuesday afternoon."