In a letter to doctors Friday, Medtronic Inc. said 13 deaths may be connected to a popular heart device wire that was recalled for safety reasons in October 2007.

At the time of the recall, the Fridley-based medical technology giant put the number of deaths at five.

The heart defibrillator lead wire, known as the Spring Fidelis, has been implanted in 268,000 patients worldwide. An estimated 150,000 remain in U.S. patients.

Defibrillators are devices implanted in the chest that shock an errantly beating heart back into rhythm. The leads, or insulated wires, connect the device to the heart.

The Sprint Fidelis lead can fracture in a small number of cases, causing the device to unnecessarily shock patients, or fail to work altogether.

Medtronic initially advised doctors not to remove the lead, which can become embedded with scar tissue in the vein. The company said the surgery to extract a lead is riskier than leaving the device intact.

A panel of independent physicians studying the issue on behalf of the company noted in Friday's letter that four of the 13 deaths linked to the faulty lead occurred during the extraction procedure.

The panel studied 89 of 107 reports, sent to the Food and Drug Administration (FDA), alleging that the Sprint Fidelis lead may have caused or contributed to a patient death. Medtronic said the panel could not determine the cause of death in the reports "with certainty" since many of them appeared to be filed by family members or plaintiffs' lawyers, and not medical professionals.

"I think the number is actually higher, but the [FDA] reporting system is not very effective in tracking deaths,'' said Randy Hopper, an attorney with the Minneapolis firm Zimmerman Reed, which has sued Medtronic on behalf of patients who say they were harmed by the lead.

Dr. Robert Hauser, a leading cardiologist with the Minneapolis Heart Institute Foundation, along with other physicians has launched a registry to track the performance of heart devices once they are implanted in patients. Regarding Sprint Fidelis he said: "I still believe that the number of deaths are rare.''

While the company still recommends leaving the leads in place, the letter Friday said if patients opt to have the lead removed, the procedure should be performed by a doctor with "extensive lead extraction experience."

Hauser said he agrees with the company's recommendation. "Lead extraction is a very complex procedure, with risks that are probably higher for death than lead failure," he said.

Janet Moore • 612-673-7752