Medtronic and the FDA told doctors to stop using the Sprint Fidelis lead last week.
What is a lead? A defibrillator contains two parts. The first is a computerized device that monitors heart rate and determines when to send jolts of electricity. The second is a lead, which is a wire covered in insulation that doctors thread through the veins. The lead stretches from the computerized device implanted near the collarbone to the heart, where it is secured into the heart muscle with screws.
Electrical signals from the heart travel through the lead to the device, and the device sends its shocks, when needed, back through the same lead.
Previously, leads had a diameter of 4 millimeters, but they are getting smaller. The smaller the lead, the easier the lead is to implant and push through the blood vessels. Medtronic's is about 2.2 millimeters. Its size might be one reason the Medtronic lead is more likely to break than older leads.
Batteries power the devices but run down after five to seven years, at which point the device is replaced surgically. During replacement, the wire lead remains and is used for the next device because the lead is difficult to remove. After years sitting in a vein, blood vessel tissue grows around the lead.
If the first wire is bad, another wire can be threaded through. Although the old wire can be removed if there's not enough room for both, about 1 percents of patients who undergo surgery die in the process.
What goes wrong with a heart device? The leads can go bad because the wire breaks (which is happening in the Medtronic cases or the insulation cracks.
When a lead breaks or cracks, the device starts to receive electrical noise and thinks the heart is not beating right. A pacemaker might send a tiny shock to the heart, but with defibrillators, patients can really feel the power. Some people describe it as being struck by lightning.
Routine checkups can sometimes give clues that a device is malfunctioning. Doctors measure the size of the electrical signal coming from the heart; how much energy it takes to pace the heart; and the impedance of the wire. Most likely, lead fractures are difficult to predict.
Heart patients who have Medtronic defibrillators need be concerned only if their lead is a Sprint Fidelis lead numbered 6930, 6931, 6948 or 6949.
A small number of other defibrillators also use the Sprint Fidelis leads. If curious, a patient can examine information that came with the defibrillator. People who find they have a potentially problematic lead should ask their doctor how often they should come in for a checkup.
Medtronic has recommendations for physicians on how to program the device to detect potential lead failures and protect a patient from surprise shocks. They can make the device less sensitive so that if it does go bad it will be less likely to deliver a jolt.
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