The Associated Press

MINNEAPOLIS — Medtronic Inc. is stopping distribution of wires that connect some of its defibrillators to patients' hearts after learning they may have contributed to five deaths.

Medtronic shares dropped more than 12 percent by midday Monday after the disclosure.

A defibrillator monitors a patient's heartbeat; if it senses an abnormal heart rhythm, it delivers an electronic shock to reset the heart to a normal beat. A defibrillation system consists of a device implanted near the shoulder with one or more leads connecting the device to the heart.

Medtronic said it discovered a "small chance of fractures in particular locations" on Sprint Fidelis models 6930, 6931, 6948 and 6949. The company is asking doctors to stop implanting the leads and return unused leads to Medtronic.

A fractured lead "can cause the defibrillator to deliver unnecessary shocks or not operate at all," said Daniel Schultz, director of the Food and Drug Administration's Center for Devices and Radiological Health.

Medtronic did not call its response a "recall," but the FDA did. However, neither the FDA nor Medtronic recommended that patients have their devices removed if no other problems have been detected.

Patients are "are more likely to experience complications from removal," Medtronic said. Instead, the company said doctors can reprogram the device to alert the patient that a fracture may have occurred. Possible indicators could include audible alerts or inappropriate shocks.

"We know it can be frightening for a patient to learn that a product they rely on so much might have a serious defect," Schultz said. "However, patients can be assured that the likelihood of fracture is very low and FDA is committed to ensuring that the risk to patients is minimized."

More than 268,000 of the leads have been implanted. Medtronic and the FDA estimated that fractures have occurred in less than 1 percent of those leads.

When the Spring Fidelis lead was introduced in 2004 it was intended to replace the Sprint Quattro leads in use since 2001. But Medtronic said it noticed that after 2 1/2 years in patients, 99.1 percent of the Quattros were still viable, but only 97.7 percent of the Fidelis leads were still viable. Medtronic said the difference between the two was not statistically significant yet but would have become signifcant as more Fidelis leads were implanted.

In a filing with the Securities and Exchange Commission, Medtronic Chief Financial Officer Gary L. Ellis said the lead problem will likely cause "significant repercussions" to the Japanese market because the company currently has no other leads approved in this market.

In addition, the company will have to account for product returns of its Fidelis lead, which won't be able to be replaced with an alternative until later this year due to a shortage of Sprint Quattro supplies. This will cause a "significant revenue reversal" in the company's fiscal second quarter.

The company said customer bulk purchase orders will either have to be adjusted or in many cases may not be able to be filled due to the limited Sprint Quattro supply.

Medtronic said the lead problems will reduce second-quarter revenue by $150 million to $250 million. Additionally, inventory write-offs will likely total about $15 million to $20 million in the second quarter, and other related costs will be $10 million to $20 million.

Medtronic senior vice president Pat Mackin emphasized that the company's action does not apply to Medtronic pacemakers.

Its shares fell $6.97, or 12.4 percent, to $49.36 in midday trading Monday.

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Medtronic advises patients with Sprint Fidelis leads to contact their doctor's office. Patients who are unsure about whether they have a Sprint Fidelis lead can contact Medtronic Patient Services at 1-800-551-5544, extension 41835, or visit http://www.medtronic.com/fidelis.