The Watchman, from Atritech

Boston Scientific has signed a definitive merger agreement, under which the company will acquire Atritech, a privately held company based in Plymouth, Minn., which developed a device designed to occlude the left atrial appendage in patients with atrial fibrillation (AF) who are at risk for ischemic stroke.

The agreement calls for an upfront payment of $100 million plus additional potential payments of up to $275 million upon achievement of specified regulatory and revenue-based milestones through 2015, according to the Natick, Mass.-based Boston Scientific, which added that the purchase price assumes no cash and no debt on Atritech's balance sheet at closing.

Atritech said its Watchman left atrial appendage closure technology could potentially offer an alternative to anticoagulant drugs for patients experiencing AF who are at high risk for stroke. The Watchman device is designed to block the opening between the left atrial appendage and the rest of the atrium, thereby preventing clots within the appendage from being dislodged into the circulation, said the company.

Atritech completed PROTECT-AF, an 800-patient randomized clinical trial of its device that demonstrated a 38 percent relative risk reduction for stroke, cardiovascular death and systemic embolism compared to long-term warfarin therapy. Atritech is currently enrolling patients in the PREVAIL study, a confirmatory study designed to gain FDA approval. The Watchman device received a CE mark in 2009.

The closing of the transaction is subject to customary conditions, but Boston Scientific expects it to be completed in the first quarter of 2011.