Medtronic Inc. has informed doctors and patients that wiring issues on its  Kappa and Sigma implantable defibrillators could cause the devices to fail. Medtronic’s letter said the issues, which could cause wires that connect the electronic circuit to other pacemaker components to separate,  could affect a total of  37,000  Kappa and Sigma pacemakers.  The company has posted a tool on its website for checking pacemaker serial numbers to determine whether a particular device could potentially have issues.

According to a letter sent to doctors,  one of the wiring issues was previously reported in a November 2005 advisory. The 2005 advisory was related to wire separations caused by a particular cleaning solvent used in manufacturing and is not related to a new Kappa/Sigma wire separation issue also discussed in the letter. There are currently an estimated 15,600 active implants from this 2005 Sigma device subset, Medtronic said.

According to a report in The Wall Street Journal, the 2005 advisory told doctors that the issue required “watchful waiting”.   But because the failure rate from this problem is higher than first thought, the company  now recommends that replacement be considered for some patients with Kappa or Sigma pacemakers.  Medtronic  said in its letter that the current risk  of  failure for the Sigma pacemakers affected by this problem is less than 4% over the lifespan of the devices.

A second, and newer separation issue affects an estimated 15,200 active Kappa devices and 6,100 active Sigma devices, manufactured primarily between November 2000 and November 2002.  The Medtronic letter said most of these devices were implanted in patients for five years or longer and may be nearing normal elective replacement time.

Medtronic said it  has observed 285 Kappa devices and 131 Sigma devices with this failure mechanism. Its modeling predicts failure rates of 1.1% for Kappa devices and 4.8% for Sigma over the remaining lifetime of these pacemakers due to this issue.  According to the letter, there is no provocative testing that can predict which specific devices may fail, and no device programming can mitigate this issue if it occurs.

Medtronic said that for most patients, device failure from either of  these issues could result in  slow heart rhythms that would cause lightheadedness or fainting, but not life-threatening complications.  These patients should seek medical attention if they experience these symptoms.

In a small number of patients who do need pacemakers to provide life-saving therapy at all times, however, such an event could prove fatal.  Medtronic’s letter said that in these cases, doctors may want to consider replacing the pacemaker.

Medtronic said it has received reports of  two patient deaths where it is possible, but unclear, whether a wire separation issue may have been a factor.