St. Jude Medical Inc. will stop selling two types of wires used in devices that treat heart failure because in some cases, conductive wires were sticking out of their insulation.

The St. Paul, Minn., company said Wednesday it will stop selling QuickSite and QuickFlex wires. St. Jude said there were no reports of patients being hurt or devices malfunctioning. The wires help the heart beat more effectively but don't deliver shocks that can save a patient's life.

It's the second time the wires of St. Jude's heart devices have been in the news in the past week. A medical journal reported last week a short-circuiting problem in St. Jude's Riata devices caused the deaths of at least 20 patients.

The company's shares fell $2.02, or 4.6 percent, to $41.78 in afternoon trading.

St. Jude said 171,000 of the wires have been sold. It estimates that in 3 or 4 percent of cases, pieces of conductors wear through the outer silicone insulation. The conductors have a separate layer of insulation. St. Jude said it received only 39 reports of the problem, but it believes the issue is only being reported in a few cases because the wires continue to work properly.

The wires are used in cardiac resynchronization therapy devices, which treat heart failure. It said the externalized conductors were found on the silicone end of wires that are placed on the lower left chamber of the heart to stimulate the left and right sides of the heart to beat in synchronization with each other. The leads connect cardiac resynchronization therapy devices to the heart.

St. Jude said the problem does not affect its newer QuickFlex or Quartet leads, which are fully insulated with a hybrid material. It said 65,000 of those wires have been sold since 2008 and no externalized conductors have been reported.

Last week a medical journal said defective wires in St. Jude's Riata and Riata ST defibrillator devices caused at least 20 patient deaths due to short circuiting. St. Jude stopped selling the devices in December 2010 because of safety concerns, but 79,000 people in the U.S. and 49,000 in other countries still have the implants. St. Jude disputes the analysis.

Jefferies & Co. analyst Raj Denhoy said the Riata devices were also taken off the market because of externalized conductors, and said Wednesday's news might suggest bigger problems and hurt the company's sales.

"The withdraw of QuickFlex and QuickSite for the same issue adds credence to the argument that there may be an inherent flaw in the material or design of St. Jude's cardiac rhythm management leads," he wrote.

Mizuho Securities analyst Michael Matson called the issue "another black eye" for St. Jude Medical.

"We think this news is likely to further aggravate St. Jude's customers and frustrate investors," Matson wrote in a note.