Athenahealth will sell itself to private-equity group Veritas Capital and Elliott Management for $135 per share, capping monthslong negotiations. The all-cash deal, valuing the health-records company at about $5.7 billion, represents a 12% premium over its share price. It will be combined with Virence Health, the Veritas-owned health care services company, and be called Athenahealth — with Virence CEO Bob Segert at the helm.