WASHINGTON -- Medtronic ( MDT) presented clinical-trial data showing that the effectiveness of its Endeavor stent didn't vary widely from Johnson & Johnson's ( JNJ) Cypher, but the device missed its primary goal in the study.

Newer stents have had trouble beating out J&J's Cypher in terms of efficacy, but that isn't the only battleground. Companies have also been competing on how easy their stents are to use, or "procedure success" as opposed to success of the device itself.

Medtronic had hoped to show that the Endeavor kept arteries from narrowing as well as the Cypher, but the company said it just missed the margin that would have met the noninferiority endpoint. J&J's Cypher was the first drug-eluting stent approved in the U.S., in April 2003.

"The study did show a significant procedure success rate in favor of Endeavor when it came to deliverability and a lower rate of in-hospital myocardial infarctions," or heart attacks, according to Dr. David Kandzari, a trial investigator and professor of interventional cardiology at Duke Medical Center.

According to the Endeavor trial data, presented at the Transcatheter Cardiovascular Therapeutics conference in Washington on Monday, the Medtronic stent showed a 98.1% procedure success rate, and the Cypher stent showed 91.2% success.

However, Dennis Donohoe, vice president for clinical and regulatory affairs at J&J's Cordis unit, the maker of the Cypher, said his company's own Cypher trials have shown a success rate of 98%.

Shares of Medtronic slipped 11 cents to $56.04.

Stents are mesh tubes used to prop open a vessel. Medtronic's trial involved 436 patients with coronary artery lesions, with 323 receiving the Endeavor stent and 113 getting the Cypher stent.

Medtronic has submitted data to the Food and Drug Administration to start the approval process for the Endeavor in the U.S. The device is currently approved for use in Europe.

According to a Medtronic executive at the conference, the company's next Endeavor trial will compare the stent with Boston Scientific's ( BSX) Taxus.