Medtronic has been alerting doctors about software updates for thousands of implantable heart devices worldwide that can experience unexpected problems.

On Tuesday, the Food and Drug Administration publicized alerts that Medtronic voluntarily sent out in late June regarding 25,000 EnTrust and Escudo implantable cardioverter defibrillators (ICDs) and 14,000 Percepta and Percepta Quad cardiac resynchronization therapy pacemakers (CRT-Ps).

"Medtronic has not received any reports of patient deaths or serious adverse events related to either issue," Medtronic spokeswoman Tracy McNulty said via e-mail. The FDA designated both actions as Class 2 recalls, meaning there may be temporary or reversible adverse health consequences or the probability of adverse events is remote.

Regarding EnTrust ICDs, Medtronic has confirmed incidents in which the older heart devices displayed warnings saying their batteries had lost the ability to deliver high-voltage therapy, even though they failed to show the early battery replacement warnings that are supposed to appear when the battery is just running low. The issue only affects high-voltage therapy, not low-voltage pacing.

Medtronic hasn't manufactured the EnTrust or Escudo devices since 2010. Although the FDA recall notice lists some 24,741 units potentially affected, Medtronic said only 2,770 of the devices remain in active use in patients, including about 200 EnTrust devices in U.S. patients. Physicians caring for patients with affected devices are encouraged to set up appointments with those patients as soon as possible to assess the issue.

EnTrust and Escudo defibrillators with less than a 2.64-volt charge remaining should be under consideration for replacement, since the battery is already low and additional software would provide minimal additional service life. For devices with more than 2.64 volts left, physicians should adjust device settings as directed and then do a battery test to decide whether the device should be replaced immediately or left in service with follow-up checks every three months or so.

Regarding the Percepta and Percepta Quad CRT-Ps, Medtronic's letter to doctors said an unintended, repetitive interaction between a nightly diagnostic system and a pacing-safety feature may eventually trigger a "full reset" that can change the device's programmed settings. Patients' devices can be updated with new software to prevent the issue at their next in-office appointment, after the treating physician gets an update to their device programmer.

Although the FDA notices list 13,718 Percepta affected units, Medtronic said about 12,364 devices were distributed before the new updates were available and about 1,300 remained in Medtronic distribution centers.