Boston Scientific Corp. has agreed to pay $295 million to buy Farapulse, a venture-backed cardiac medical device company it already owns a stake in, as the California firm works toward U.S. approval for its non-thermal atrial-fibrillation treatment.

Boston Scientific, which designs and manufactures other minimally invasive heart devices in Minnesota, has agreed to buy Farapulse in a deal valued at $450 million plus milestone payments. The upfront payment is lower because Massachusetts-based Boston Scientific already owns 27% of Farapulse, having first invested in 2014. Boston Scientific plans to buy the remaining shares in the third quarter.

Farapulse got approval to sell its "pulsed field ablation" system in Europe during the first quarter, becoming the first company to commercialize a technology that can ablate heart tissue to treat atrial fibrillation without applying heat or extreme cold, Boston Scientific said.

A clinical trial is underway in the U.S. to gain Food and Drug Administration approval, with more than 100 patients with intermittent atrial fibrillation already enrolled in the prospective, randomized trial comparing the Farapulse PFA System with conventional ablation. The trial will measure how many patients have no atrial fibrillation 12 months after a single PFA treatment.

"The Farapulse PFA System is intended to enable physicians to precisely ablate cardiac tissue while minimizing procedural complications, and real-world and clinical evidence from trials throughout Europe have demonstrated encouraging, positive results," said Dr. Kenneth Stein, chief medical officer for Boston Scientific's heart-rhythm device unit, in a release.

Also called "AFib" or AF, atrial fibrillation is the most commonly treated heart-rhythm problem in the U.S., and was mentioned as the underlying cause of death in nearly 26,000 U.S. death certificates in 2018, according to studies cited by the CDC. The condition increases a person's risk of having an ischemic stroke by at least fourfold.

AF happens when the upper chambers of the heart quiver or beat out of sync with the rest of the heart, interrupting normal flow of oxygenated blood and creating the risk that blood will pool and form clots.

Ablation is a common AF treatment in which the doctor uses an energy source to burn or freeze specific swaths of heart tissue. Scarring afterward is supposed to block the errant electrical signals in the heart driving the AF. Farapulse cites studies that say traditional ablation "may carry risk to surrounding structures" such as the esophagus or phrenic nerve.

Instead of heat or cold, the Farapulse system uses an electric field that is "optimized purely for PFA and carries no legacy design elements of traditional thermal ablation," the Farapulse website says. The device is delivered to the heart inside a thin catheter, unfurled inside the ventricle, and then removed once the procedure is over.

Boston Scientific says the device is part of a $6 billion market for electrophysiology treatments that is growing more than 10% a year. The deal isn't expected to be profitable on an adjusted basis this year or next, though the company will offset losses internally through undisclosed "cost efficiencies and trade-offs."

Pending regulatory approvals, the deal will carry an upfront payment of roughly $295 million and up to $92 million in additional milestone payments over three years.