A Minneapolis cardiologist who studies device failures said Tuesday that there are enough questions about a new coating that St. Jude Medical Inc. uses on defibrillator wiring that physicians should stop using it until more is known.

Dr. Robert Hauser of the Minneapolis Heart Institute had previously connected at least 20 deaths to an earlier generation of defibrillator leads, the wiring that runs from the device into the heart.

Little Canada-based St. Jude has pulled those products from the market, but Hauser now says his work indicates that newer products are not immune to the underlying problem, in which the coating of the wires wears away.

"I'm not saying it's a bad lead," Hauser said. "I just don't know if it's a good one."

Hauser's report, published Tuesday in the online journal Europace, had been anticipated by analysts and industry-watchers for weeks.

St. Jude has said defibrillators with its new Optim coating, which insulates wires on the company's Durata and Riata ST Optim defibrillator leads, are among the most wear-resistant and safest on the market. The company says the coating is 50 times more abrasion-resistant than standard silicone-only leads.

But while Hauser found that the Optim-coated leads are not immune to abrasion, he did not find instances of wires working their way outside the insulation of the Durata leads. Such "inside-out" abrasion has plagued St. Jude's now-recalled Riata defibrillator leads.

Still, in some cases the abrasions to the Optim-coated leads resulted in high-voltage failures and one death. What is not known -- and requires more study, Hauser said -- is how often Optim leads fail because of damaged insulation.

St. Jude spokeswoman Amy Jo Meyer said St. Jude never claimed Optim leads were abrasion-free. She said the company conducted detailed analyses of its leads -- and the data Hauser used for his report -- and determined "the overall performance and high reliability of the Durata lead is comparable to other defibrillation leads on the market."

A lead is an insulated wire that attaches an implantable defibrillator or pacemaker to the heart. The lead runs from the device, usually placed just under the skin of the upper chest, into the heart and delivers an electric shock to restore normal heart rhythm or restart a heart that stops.

Last week, the FDA announced that it is requiring studies of the Riata and other recalled St. Jude leads. It recommended patients with Riata leads get flouroscopic X-rays to check for abnormalities. And it required that Little Canada-based St. Jude study its Durata leads.

St. Jude has touted the durability of Durata and its other Optim-coated leads as the bad news about Riata became more frequent. In May, the company noted that its study of Optim-coated leads showed no instances of externalized conductors caused by inside-out abrasion. In addition, the leads had a "99.96 percent rate of freedom from all-cause insulation abrasion" and "99.84 percent rate of freedom from all-cause mechanical failure."

Hauser gathered data from the FDA's Manufacturers and User Device Experience (MAUDE) database on April 13, searching for reports of lead abrasion. He said he found 15 reports for Riata ST Optim and 37 reports for Durata leads. The reports had been submitted by St. Jude Medical between December 2007 and January 2012, based on its analysis of returned leads.

Eight of 15 Riata ST Optim leads had "can" abrasions from rubbing against the defibrillator itself and three abrasions were most likely caused by friction with another lead. Four of these abrasions resulted in high-voltage failures and one death, Hauser said. In the Durata reports, 12 had "can" abrasions and six had abrasions caused by friction with another device. Of these 18 abrasions, Hauser said, 13 had electrical abnormalities.

Market reaction

Last week, after the FDA announced it was requiring St. Jude to study Riata and Durata, the company's stock price fell more than 4 percent. On Tuesday, the company's stock was down less than 1 percent, falling 21 cents to $37.96.

In a note to investors, Goldman Sachs referred to Hauser's report as "Mostly smoke, no fire."

Thomas Gunderson, a medical technology analyst at Piper Jaffray & Co., on Tuesday said with the publication of Hauser's study, "the investors' perceived risk of a bigger problem with Durata has been reduced."

Without a way to compare Durata abrasion rates against leads made by competitors Boston Scientific and Medtronic, Wall Street investors can conclude there "really is not much negative impact," Gunderson said.

Hauser said he is planning to begin a multi-center study in January to look at the rate of abrasion in Durata and other Optim-coated leads, and to what extent abrasion is related to lead failure.

St. Jude Medical said its product registries are monitoring 11,000 patients with Optim-coated leads, with plans to follow those patients indefinitely.

James Walsh • 612-673-7428