CHICAGO —  Guidant Corp. (GDT) Friday said it advised doctors to stop implanting some of its defibrillators, which U.S. regulators may recall, sending the medical device maker's shares down nearly 11 percent.

Continuing reports of problems with the company's key cardiac devices have pressured the stock and raised concerns that Guidant's deal to be acquired by Johnson & Johnson may be in jeopardy.

Guidant shares fell to $61.20, down 10.8 percent from Thursday's close of $68.60 on the New York Stock Exchange (search).

Guidant said it is advising doctors about safety problems with its Contak Renewal 3 (search) and 4, Renewal 3 and 4 AVT, and Renewal RF implantable cardioverter defibrillators (search), or ICDs.

The devices are designed to protect patients from life-threatening heart rhythms, but a number of them have been subject to a component failure that may limit available therapy.

Guidant said it has determined that a magnetic switch in these devices may get stuck in the closed position, which in some cases inhibits their ability to treat ventricular or atrial tachyarrhythmias and can accelerate battery depletion.

Four incidents have been confirmed out of about 46,000 devices; a fifth is suspected but cannot be confirmed, the company said.

In the four occurrences in which the device was implanted, the device sounded a warning that alerted patients or their physicians of the defect, and the devices were replaced.

One other incident occurred in a device before it was implanted.

Guidant said it would establish an independent panel of experts to recommend guidelines for when to disseminate information to physicians and patients about life-sustaining implantable devices.

It said it would cooperate with and enlist the support of other interested parties, including the U.S. Food and Drug Administration, patient advocates, and physician societies.