The Food and Drug Administration has given Boston Scientific Corp. the go-ahead to market its most sophisticated heart defibrillators to a broader pool of patients suffering from heart failure.

Boston Scientific may now sell the $35,000 implantable heart devices, called CRT-Ds, for use in some patients suffering from mild heart failure, a condition where the heart cannot pump enough blood to meet the body's needs.

The news could pump new life into the sluggish $6 billion market for heart rhythm devices -- one way to do that is to expand the number of people who can be treated with a device that regulators have already approved for a limited range of uses. About 6 million people in the U.S. have been diagnosed with heart failure.

Natick, Mass.-based Boston Scientific, which employs about 5,000 in the Twin Cities, said Thursday's approval means an additional 100,000 to 140,000 patients in the United States could benefit from the therapy. The company expects the expanded pool of potential patients could result in an additional $150 million to $175 million in sales in the United States, and $250 million to $350 million worldwide.

Overall, it's been a tough year for Boston Scientific, which reported a 38 percent decline in second-quarter profit after pulling all its defibrillators, including CRT-Ds, from the market for a month last spring after a record-keeping error was discovered.

Wells Fargo Securities analyst Larry Biegelsen said in a note to investors Thursday that the most recent approval is a "modest market opportunity." While some doctors have already used the device in patients suffering from less-severe strains of heart failure, the FDA's action will now permit Boston Scientific to market the device more aggressively, he said.

The FDA's action was based largely on a landmark clinical trial that followed 1,820 heart failure patients in the United States, Europe, Canada and Israel for three years -- an extremely large study for a medical device. The clinical trial found that the CRT-D device reduced the risk of death or heart complications by 57 percent in patients who have an abnormality caused by delayed contraction of the heart, according to Boston Scientific, which funded the study.

Stopwatch-sized CRT-D devices are implanted under the skin and feature a defibrillator, which shocks an irregularly beating heart back into rhythm, combined with resynchronization therapy to coordinate the beating of the left and right ventricles, facilitating blood flow throughout the body. The device is usually used along with drugs to treat heart failure.

The FDA said the rate of complications in the study was "acceptable," but it's requiring Boston Scientific to conduct two post-approval studies to track potential complications in patients implanted with the device.

Although Boston Scientific didn't release news of the FDA's action until after the markets closed, the FDA inadvertently posted the news on its website for a brief period Thursday afternoon. Shares of Boston Scientific closed Thursday at $5.45, up 6 cents.

Janet Moore • 612-673-7752