A three-year trial comparing Abbott Laboratories‘ Xience V drug-eluting stent against its Taxus competitor from Boston Scientific Corp. showed that the Abbott device is much more effective three years after implantation.

The news, announced at an American College of Cardiology conference in Orlando, sent the Natick device goliath’s stock into a slight swoon. The Xience product is already outselling the Taxus, and the news promises to accelerate that trend.

The first full day of trading after the news broke, Monday, March 30, saw BSC shares open at $7.98 (after closing at $8.19 the previous Friday), top out at $8.10 and close at $7.96 — a 2.5 percent slide. BSC shares were trading at $8.05 as of about noon March 31.

Abbott shares enjoyed a better ride, closing Friday, March 27, at $46.60, opening March 30 at $47.11, peaking at $47.99 and closing at $47.89 — up 1.7 percent. As of about noon March 31, Abbott shares were trading at $48.19.

The international SPIRIT II study of 300 patients, which Abbott sponsored, showed that rates of major cardiovascular events for the Xience stent topped out at 6.4 percent during the second and third years; the Taxus device hit 10.5 percent for the second year and 14.9 percent for the third year.

The Abbott stent also showed a lower mortality rate than the Taxus, although neither caused a large number of deaths or serious complications.

One wrinkle is that Boston Scientific also markets Xience under the private-label Promus brand, though it pays back royalties to Abbott from those sales.