Following a patient death, Medtronic PLC is voluntarily recalling hundreds of big-ticket HVAD heart pumps made by HeartWare, a company it acquired for $1 billion this summer.

On Friday, Medtronic announced that the Food and Drug Administration is classifying two recent HeartWare safety letters as Class 1 actions, the highest-risk category, reserved for situations with a reasonable probability of serious health consequences including death. Medtronic was aware of the two safety letters before it closed the deal to acquire HeartWare on Aug. 23.

Both safety letters involve problems that can happen when moisture interacts with electrical components in HeartWare's flagship product, the HVAD. HeartWare's HVAD uses a small, magnetically driven impeller implanted near the heart, plus an external controller and battery pack, to circulate a patient's blood following the onset of end-stage heart failure.

With list prices well above $100,000, ventricular assist devices like the HVAD are among the most expensive implantable medical devices that a doctor can prescribe.

Last May, HeartWare sent out a worldwide urgent safety notice regarding about 8,800 HVAD external controllers that had connectors that were potentially susceptible to coming loose and allowing moisture to get in. Moisture damage to the controller could cause the pump to stop working or make it harder to detect an alarm. The affected model Nos. were 1400 and 1401.

Nearly all affected doctors worldwide have acknowledged receiving the May alert, which recommended they inspect patients' controllers and replace them if needed at the patients' next regular checkup. More than 300 such controllers have been replaced so far.

On Aug. 15. HeartWare sent out a second urgent safety notice, asking hospitals to inspect their stock of un-implanted HVAD pumps and return certain models that could be susceptible to moisture damage. Those models were Nos. 1103 and 1104.

The notice said the HVAD driveline, which is the wire that connects the pump inside the body to the controller outside the body, could become contaminated with fluid and lead to problems with the component that connects the driveline to the controller.

"Foreign material at the driveline/controller connector could lead to electrical faults and connection failures," said the notice, which has been acknowledged by most of the doctors it was sent to. "In these scenarios, potential risks include interruption of circulatory support due to a pump stop, which could cause serious injury or death."

A Medtronic spokesman said via e-mail Friday that one patient death was reported as potentially related to "fluid ingress into the controller and a short of the controller's power circuitry."

As of Sept. 26, company officials said 323 of the 350 potentially affected pumps had either been implanted or returned to the maker. The safety notice said the issue has been seen most often in the 30 days after implant, and devices that are already implanted are not subject for removal.

Joe Carlson • 612-673-4779