Guidant ( GDT) shares fell Thursday after the company confirmed that its experimental drug-eluting stent has run into quality-control problems that will delay its launch. In a special conference call to discuss the state of its stent, which is used to treat clogged arteries, Guidant said it is making refinements to its manufacturing processes and will be improving the overall quality of the device. The moves will delay the company's plan to file for U.S. approval for the stent by six to eight months, pushing off its filing date until the first quarter of 2005. Shares of the company fell 38 cents, or 0.7%, to $55.50. Five weeks ago, Guidant warned that a limited number of stents failed to meet the company's performance standards or quality standards in preclinical trials. Guidant discussed the quality-control issue with the FDA and said it has structured a plan that will not require the company to perform further testing of the stent. Competition in the stent market is heating up and Guidant doesn't want to fall too far behind rivals Johnson & Johnson ( JNJ) and Boston Scientific ( BSX), both of which already have stents on the market.