Xconomy -- Rhythmia Medical, a Burlington, MA-based maker of catheter-based systems for mapping the heart, has brought in $5 million of a planned $7 million equity offering, according to an SEC filing. The financing comes from eight investors, according to the filing, and brings Rhythmia’s total funding pot to $17 million. Earlier this spring, Ryan wrote about the startup’s plans to raise more capital to put towards the quest for regulatory approval and commercialization of its device, which is designed to form a 3D image of the heart in order to target the tissues responsible for irregular heartbeats.