Stock in AtriCure Inc. dropped nearly 11 percent today on news that the West Chester company has agreed to acquire a North Carolina-based competitor, nContact Inc., for up to $149 million. Shares in AtriCure (Nasdaq: ATRC) declined from a previous close of $22.45 to $20 by midday. The stock has ranged from $13.19 to $28.15 over the last 52 weeks. AtriCure is best known for making medical devices to treat atrial fibrillation, a common malady characterized by an irregular and fast heartbeat.