By ASHLEY M. HEHER
Associated Press

INDIANAPOLIS — Guidant Corp. said Friday it was telling doctors to stop using five models of its implantable cardiac defibrillators because a faulty switch could cause it to malfunction.

The announcement was the Indianapolis-based company's second safety advisory in a week for its defibrillators and covered two devices that last week it said could be repaired with reprogramming in a doctor's office. The company's shares tumbled 9.4 percent, or $6.42, to $62.18 in morning trading on the New York Stock Exchange.

The five devices included in the latest announcement are the Contak Renewal 3 and 4, Renewal 3 and 4 AVT, and Renewal RF. About 46,000 of the devices are in use, the company said.

Guidant said doctors "should discontinue implants of these devices pending further notice."

The company said it had informed federal regulators of its action and that the U.S. Food and Drug Administration may classify it as a recall. Officials with the FDA were not immediately available for comment.

The devices listed Friday have had at least four malfunctions. A fifth suspected case has not been confirmed, but no patients have been injured, Guidant said.

Guidant last week said five other models had flaws. It said some of those devices have memory problems and can be reprogrammed without removal, but nearly 29,000 of the defibrillators - 20,000 implanted in U.S. patients - can't be fixed externally.

At least two patients with those defibrillators have died, and the company said those devices had failed at least 45 times.

An implantable defibrillator, smaller than a pack of cigarettes, is intended to sense an irregular heart rhythm and shock the heart back into correct beating.

The five defibrillator models cited by Guidant on Friday have a magnetic switch that can become stuck in a closed position, preventing the device from treating irregular heart rhythms. The faulty switch can also limit a defibrillator's battery life.

"Guidant works diligently to create the most reliable products and services, enhance patient outcomes, and limit adverse events to patients," company spokesman Steve Tragash said in a statement. "The actions taken today and over the last several weeks reflect our commitment to expand physician and patient communication."

Guidant shareholders in April approved a $25.4 billion acquisition by Johnson & Johnson.

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