INDIANAPOLIS (AP) _ Guidant Corp. has asked doctors to monitor patients who wear certain Guidant pacemakers, saying the batteries that power the devices can wear out much sooner than expected.

About 7,500 Discovery, Meridian, and Pulsar brand pacemakers _ less than 1 percent of those sold _ are affected with the problem, a Guidant spokeswoman said. Batteries in the units typically last seven years, but could drain in six months, the company said.

Physicians have been instructed to examine patients with the affected devices on a monthly basis for up to six months for signs of premature battery failure.

Some patients with the faulty devices could require a new unit, which the company will replace for free, the company said. No deaths or serious injuries have been observed due to premature battery failure in the units, Guidant added.

Shares of Guidant fell $1.50 to close at $60.50 on the New York Stock Exchange.

Indianapolis-based Guidant manufactures heart defibrillators, pacemakers, and other products for the heart and vascular system.