An implantable defibrillator is a device that monitors your heart rate. It uses batteries to send electric signals to a heart that's beating too slow.
But what if the lead wires prove defective?
On Monday US defibrillator-maker Medtronic announced was suspending sales of an electrical wire that connects the hearts of 235,000 patients world-wide to the defibrillators implanted in their chests, saying they may have contributed to five deaths.
The wire in question, called a lead, is prone to fracturing within patients' blood vessels and erroneously dispatching a massive electrical jolt, the Minneapolis-based Medtronic said. This jolt can be uncomfortable at best, and at worst may itself have contributed to one or more of the deaths.
Still Medtronic wont advise surgical removal of the leads of the devices already implanted. Well, not because the risk is low, but only because the risk from the surgery to remove the wires from the veins that carry them to the heart could be more potentially dangerous than that of leaving the leads in.
The company is only recommending that patients who think they have the wires in their bodies should contact their doctors, who can reprogram their defibrillators to better monitor and warn of problems with the leads.
Cardiologists have long known that leads are more fragile than the devices they're connected to, and in the past, recalls of similar devices have cost companies millions. For example, Medtronic has experienced malfunctions in its heart-device leads in the 1980s and again in 1991, when it issued a safety alert to 20,000 doctors about leads' gradually losing their ability to carry electricity.
There are 268,000 of the Sprint Fidelis leads that were implanted in patients, but it is believed that about 235,000 patients now have them in their bodies. The devices that would use the faulty leads also are known as ICD's (for implantable cardioverter-defibrillator) and CRT-D's (for cardiac resynchronization therapy-defibrillators). This latter form of complex, hybrid device not only can deliver the massive shock but can also provide extra pumping power in the hearts of patients with congestive heart failure.
Heart defibrillators, along with the electrical leads, are designed to sense when a patient's heart has begun beating too fast, often in the lethal fast-quivering state called fibrillation. The device senses that the heartbeat has gone haywire and the shock, when appropriate, can save a patient's life by propelling the heart back into normal rhythm.
When a Medtronic Sprint Fidelis lead fractures, three things can happen, two of them bad. It can simply beep, alerting the patient to consult his physician immediately. Or it can cause a massive, unnecessary shock akin to getting kicked in the chest by a horse. Third, it can cause the defibrillator battery to deplete, which could cause the device to fail to deliver a necessary life-saving shock.
Medtronic's Sprint Fidelis leads are used only in cardiac defibrillators -- or complex devices with defibrillation capacity -- and not in conventional pacemakers. Some patients with congestive heart failure use devices that include this defibrillation ability, and those would be among the machines that use the Sprint Fidelis lead.
Regarding the deaths, Medtronic officials said some involved inappropriate shocks, without specifying the cause of death. Other of the deaths, the officials said, involved battery depletion such that the defibrillator failed to dispatch an electrical shock when it was necessary to save a patient's life.
The company said it has learned through 30-month performance data that the Sprint Fidelis had begun to fail at a greater rate than that of another top Medtronic lead, called the Sprint Quattro.
The company's data showed that the Sprint Fidelis maintained 97.7% "viability" at 30 months, compared with 99.1% in the Sprint Quattro. Medtronic said that the numbers aren't yet statistically significant, but that "if the current lead fracture rates remain constant, it will become so over time."
Even with a failure rate of 2.3% the problem could far exceed the risk factor in the case of the Guidant heart devices, which was generally expressed in terms of 1 in 1,000, or 1 in 5,000. In an interview, David Steinhaus, medical director of Medtronic's cardiac-rhythm disease management unit, said most of the 2.3% failure rate relates to fractures as opposed to other causes. He said that historically fractures had been a concern in leads and that there have been other cases of defibrillators going off inappropriately.
While many details remain imprecise -- and Medtronic largely refrained from discussing the death cases -- this product removal could prove significantly larger in scope than the problems that arose in 2005 involving defibrillators and pacemakers made by another firm.
Steinhaus said the company viewed the defects in the Sprint Fidelis leads "as a very low risk," but "we're being super-cautious and conservative about this."
Nevertheless, the admission could hurt Medtronic, which is the world's bigger seller of cardiac-electrical devices, such as defibrillators and pacemakers. It has about 50% of the $6-billion-plus defibrillator market.
Attention is also turned on the FDA's oversight of medical devices, which are regulated under different standards than drugs. For instance, the Sprint Fidelis leads, which went on the U.S. market in 2004, weren't required to be tested in humans before they won FDA approval. Previous versions were tested in humans, but the Sprint Fidelis models weren't different enough from those earlier iterations to require human trials, the FDA said.
Medtronic says it did start clinical trials for two of the four Sprint Fidelis models before they were sold in the U.S., one in 80 patients and the other in 81 patients, but didn't include these in its FDA application because they weren't required. The devices "passed the objectives of the study," which wasn't designed to assess long-term fracture risk, a Medtronic spokesman said.
Medtronic said in a letter to physicians this March that its investigation suggested that "variables within the implant procedure may contribute significantly to these fractures," an issue that potentially would arise only when doctors actually placed the devices into humans.
Before approving the Sprint Fidelis models, the FDA reviewed results from animal tests and extensive engineering "bench" studies, including 400 million repetitions of a bending motion designed to answer questions about the devices' strength, said Megan Moynahan, chief of the FDA branch that oversees defibrillator leads. Because the fracturing issue is "extraordinarily rare," a human clinical trial was unlikely to find it, she said.
Ms. Moynahan said the agency began watching the devices more closely in February. But "the lead didn't appear to be performing any differently" than other similar products, she said, and there wasn't a clear signal of a problem. "We've had this closely on our radar and our concern has been building," she said.