Dr. Robert G. Hauser. Image Source: Minneapolis Heart Institute

A new study in the journal HeartRhythm reveals that the potential of Sprint Fidelis lead failure increases, mainly due to the device's "fatigue mechanism," while the failure rates of other defibrillator leads are low and stable, lead researcher Robert G. Hauser, MD, told Cardiovascular Business News.

Hauser attributes the device's tendency to fracture to its fatigue mechanism. "Over time, the lead is subjected to all sorts of mechanical stresses, and it's just a matter of having the stress on the weak point long enough until it fails," explained Hauser, a cardiologist at the Minneapolis Heart Institute. "We've also observed that the lead fails earlier in younger people who are more active, and who have functionally normal hearts."

The Medtronic Sprint Fidelis defibrillator lead was found to be prone to fracture and recalled in October 2007, after 665 failures and five reported deaths. Hauser and co-author David L. Hayes, MD, from the Mayo Clinic in Rochester, Minn., approximated that 150,000 patients are at risk for sudden death currently have Sprint Fidelis leads in the U.S.

During the study's 1.3 years of follow-up, 94 of 3,037 defibrillator leads failed (1.65 percent per year). Out of those 3,037 leads implanted, 848 were Sprint Fidelis. Out of the 94 leads that failed altogether, 72 were Sprint Fidelis, making their failure rate 8.5 percent. If these findings hold true in a real-world population, and 150,000 people currently have Sprint Fidelis leads implanted in the U.S., 12,750 of those patients could experience lead failure.

Hauser and Hayes wrote that the "cumulative hazard of Sprint Fidelis failure was significantly greater compared to 2,189 other defibrillator leads, and the hazard of Sprint Fidelis failure accelerated after the first year and continued to increase during the study."

In November 2008, Medtronic released the survival rates for its Sprint Fidelis lead models 6949, 6948, 6931, 6930, using its CareLink network and System Longevity Study (SLS) data. The company's data showed a 42-month survival rate of 96.2 percent for CareLink network and 93.7 percent for SLS data. The statistics compare to one-year survival rates of 99.8 percent for CareLink network and 98.7 percent for SLS data, which are much higher survival rates than Hauser Hayes found in their study.

In contrast to other defibrillator leads in the HeartRhythm study, the Sprint Fidelis failure rate was significantly higher (3.75 percent per year vs. 0.58 percent per year). After three years of implantation, 87.9 percent of the Sprint Fidelis leads were working compared with 98.5 percent for the other models.

Hauser said that the largest model-type studied was the Medtronic Sprint Quattro at approximately 1,300 leads. He noted that the Quattro "did very well" within the study period, as did the Boston Scientific's Endotak Reliance. He said that though there were not a large number of St. Jude Medical's leads, however, within the small sampling "there were no red flags."

Importantly, Hauser and Hayes wrote that the chance that a Sprint Fidelis lead would survive another year decreased progressively during the study. They wrote that Sprint Fidelis failures were caused by pace-sense conductor fracture (87.5 percent), which caused inappropriate shocks in 36 of 72 patients.

Based on these findings, questions arise on how to manage these at-risk patients. "We are not recommending that physicians replace these leads prophylactically. One decision point is what to do with the patient with a generator, whose battery is running down, and they present at the hospital at the hospital for pulse generator replacement--should you replace the lead at that point in time?" Hauser said. "We are suggesting that physician should evaluate each patient from a risk standpoint, taking into account whether the patient has been treated for ventricular fibrillation or ventricular tachycardia by the device or do they have an underlying rhythm, etc."

However, he cautioned that once a lead has been implanted for four years, the difficulty in extraction increases. He also stressed that the experience of the physician is another tremendously important component of lead extraction and replacement because "the procedure is not without risk. Therefore, it is an individual patient-by-patient decision, and cannot be construed into a broad policy statement."

In response to these concerns, Medtronic has introduced a new alert system, which the Minneapolis-based company said works 76 percent of the time to give patients at least three days warning of a fracture. Hauser said that over the past four to five months, the new algorithm "is working better, and we are avoiding inappropriate in most of our patients-not all, but most. The new algorithm has been a good addition to the monitoring techniques."

Even though many class action lawsuits were filed against Medtronic concerning the faulty Sprint Fidelis leads when they were initially taken off the market, the company is currently shielded under the Supreme Court's ruling in Reigel vs. Medtronic, which found that patients cannot sue manufacturers of medical devices approved by the FDA. Just last week, the Wisconsin Supreme Court dismissed a case against Medtronic, ruling that federal law preempts state claims against FDA-approved medical devices.

However, the Supreme Court only protects medical device companies that comply with the FDA pre- and post-marketing procedures, so questions remain if blame can be placed and on whom. "When we become aware of the problem in January 2007-when we had seven failures-I examined the FDA database, in which Medtronic had reported hundreds of problems with the Sprint Fidelis leads. The company must have been aware, at some level, of the company that there were fractures. Unfortunately, they hadn't compiled a good post-market study," Hauser said.

"This whole pre-emption thing is unfortunate. The fact that companies have had to be concerned about lawsuits has provided an additional safety net for patients," he commented. "Now, companies are basically immunized about litigious actions."