Boston Scientific (BSX +2.7%) bucks a down tape this morning on an upgrade to Buy at Citigroup. The firm says BSX is positioned to be the biggest winner from St. Jude Medical's (STJ -1%) Durata troubles. Citi expects it will be taken off the market within six months, and the ripple effects are likely to cost STJ around $820M in annual sales. BSX could easily take 41% of that market share, with Medtronic (MDT -0.9%) absorbing around 29%. Citi's upgrade differs widely from comments made on Friday by BofA Merrill, which put the risk of a Durata recall well below 50%.