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ANAHEIM, Calif. -- Researchers said an experimental drug that interferes with the genetic workings of blood-vessel walls proved effective in a new study against a common problem faced by heart surgery patients: the tendency of veins used in bypass surgery to clog up in the years after surgery.

Each year about 350,000 patients undergo bypass surgery, in which veins taken from the leg are used to reroute blood flow around blockages in coronary arteries. But the veins, which aren't designed as arteries are for the high-pressure, high stress environment, often gradually become obstructed themselves. About 30% to 50% of such vessels fail within 10 years, often resulting in the need for invasive procedures to clear them out or even a repeat bypass operation.

The new drug, which researchers refer to as an E2F decoy, is intended "to suppress the genetic trigger" that in the face of the pressure causes proliferation of the unwanted tissue, said Eberhard Grube, chief of cardiology at the Heart Center in Siegburg, Germany. He presented data on a randomized study involving 200 patients at the annual Scientific Sessions of the American Heart Association here.

The drug is a solution containing short strands of DNA that mimic the genetic instructions cells in the vessel wall use to make the material that fills it up. After harvesting the vein from a patient's leg, researchers using a special device fill the vein with the solution, exposing cells in the vessel wall to the decoy DNA for about 10 minutes. The idea is that the decoy DNA will prevent the cell's actual genetic instructions from being activated, reducing the likelihood that the vessel would become obstructed.

The study is based on research initially developed by Victor Dzau and Michael Mann of Brigham and Women's Hospital and Harvard Medical School, Boston. They did a previous study indicating the treatment was effective in patients who underwent surgery to bypass obstructions in leg arteries. The new report was sponsored by Corgentech Inc., a closely held Palo Alto, Calif., company that is hoping to bring the drug to the market.

In the study, researchers were able to evaluate 136 patients and a total of 309 vein grafts one year after surgery; 172 of the vessels had been bathed in the E2F decoy and 137 had been exposed to a placebo solution. The vessels were considered to have failed if they were entirely clogged or obstructed by 75% or more.