A Danish study of the recalled Riata and Riata ST defibrillator leads made by St. Jude Medical (NYSE:STJ) suggests that the problem that prompted the recall – so-called “lead externalizations” in which the lead wires wear through their insulation – is linked to electrical failures and worsens over time.
The study, "Prospective Nationwide Fluoroscopic and Electrical Longitudinal Follow-up of Recalled Riata Defibrillator Leads in Denmark," published this month in Heart Rhythm, followed 295 Danish patients who were implanted with the Riata leads. The subjects had the leads for 5.1 years (±1.1 years); the cohort initially had 34 instances of externalized conductors and 19 electrical abnormalities. The patients were followed until death, lead discontinuation with fluoroscopy or a new screening in 2013 with fluoroscopy and device interrogation.
The researchers, led by Dr. Jacob Larsen of Denmark’s Aalborg University Hospital, found that in 27 of those patients who began the study with EC, the length of the externalizations increased by 4mm (±1mm) after 1.1 years (±0.3 years). There were 8 more instances of overt EC and 2 instances of borderline EC after 1.1 years (±0.2 years), for an incidence rate of 3.7 per 100 person-years (95% CI, 2.0 – 6.9).
Electrical follow-up in 276 patients with normal baseline electrical function demonstrated 20 incident electrical abnormalities after 1.0 years (±0.3 years) for an incidence rate of 7.1 per 100 person-years (95% CI, 4.6-11.0). Riata and Riata ST leads with baseline EC were more than 4 times more likely to develop electrical abnormalities than leads with no evident EC, the researchers wrote.
"The development of EC is a dynamic process despite long lead dwell time. EC are associated with a higher risk of electrical abnormalities. Therefore, lead replacement should be considered, especially in patients with long life expectancy," they wrote.
The data from the smaller Danish study are slightly higher than data from St. Jude’s ongoing, 776-patient Cardiac Lead Assessment Study, a multi-center, prospective study showing that leads with EC had electrical failure 3.1% of the time, compared with 2.0% of the non-EC leads.
"The incidence of new EC after 1 year in the study was 2.0% in 7F [Riata ST] leads and 4.3% in 8F [Riata] leads (p = 0.23). During a mean follow-up period of 19.7±7.8 months (mean±stdev), a total of 17 leads (5 with EC, 12 without EC) were identified as having electrical dysfunction," according to St. Jude’s most recent product performance report.
Apart from the CLAS study, St. Jude said the number of reports it’s received from the field about externalized conductor rates shows a nearly 2.1% EC rate for the Riata leads and a nearly 0.9% rate for the Riata ST leads.
"St. Jude Medical understands that the passive system of complaint reporting and returned product analysis results in under-reporting and hence underestimates the true failure rate associated with any given failure mechanism. This is especially true for externalized conductors since most manifest as visual anomalies only with normal electrical performance. While acknowledging these limitations, St. Jude Medical provides externalized conductor rates from the passive data system to maintain continuity with previously published data and to provide full disclosure of the data available to St. Jude Medical. As of Feb. 28, 2014, there were 3,802 cases of externalized conductors reported to St. Jude Medical worldwide on Riata (8F) and Riata ST (7F) silicone defibrillation leads, equating to a 2.07% (3224/156,000) incidence rate for Riata (8F) and 0.82% (578/70,600) for Riata ST (7F) leads. Of these 3,802 leads, 2,930 were not returned and 872 were returned for analysis," according to the report.
Larsen cautioned that the Danish study does not establish a causal connection between externalizations and electrical abnormalities or whether ECs are a marker for "potentially failing ‘stressed’ leads," he told heartwire via email.
"We cannot tell from the available data. But the data strongly suggest that a recalled Riata lead with visible externalization is associated with a higher risk of electrical abnormalities in the clinical setting," Larsen wrote.
The problem is compounded by the fact that leads without any evident externalizations "also have a higher rate of electrical abnormalities than seen for contemporary benchmark leads, and fatal electrical failures with short circuits in the pocket area or under shock coils have mostly been associated [with] leads without externalizations in previous studies and case reports," he added, noting that a normal fluoroscopy study "is not sufficient to reliably risk-stratify the patients with recalled Riata leads."
Dr. Laurence Epstein of the Brigham & Women’s Hospital in Boston said the study demonstrates that "the electrical failure rate is much higher than people had thought" and "is linked to cable extrusion," according to the website.
"[T]he leads have this potential to fail, and a potential to fail in a catastrophic way, when the patient needs the device to save their life, but it shorts and doesn’t deliver therapy," Epstein told heartwire, adding that the Danish study likely underestimates the scope of the problem.
"At high-volume centers with excellent outcomes, I think being more aggressive with these leads is warranted," Epstein said. "I think leaving these leads behind is going to be dangerous. The bottom line is this: It’s never [going to be] easier to take the leads out than it is today."
