March 29, 2012 (Chicago, Illinois) — It was a disturbingly high rate of insulation failures seen with implanted St Jude Medical Riata ICD leads that led to a physicians-only brainstorming "summit" outside Minneapolis one day in January. The resulting electrical abnormalities seemed to be triggering inappropriate shocks and maybe even preventing some appropriate ones. Most graphically, many of the failures showed up at fluoroscopy as silhouettes of the leads' internal cables poking through abraded silicone insulation. But that much-discussed problem wasn't the end of it.
For some here at the American College of Cardiology (ACC) 2012 Scientific Sessions, the focus is shifting away from Riata insulation breaches per se and toward what researchers are describing as a less common but related and potentially more serious short-circuit risk.
Such shorts in the high-voltage leads, in particular, have occasionally been fatal, according to a presentation at the ACC sessions by Dr Robert G Hauser (Abbott Northwestern Hospital and Minneapolis Heart Institute, MN), who had helped organize and run the January summit.
"While investigators have focused on externalized cables, our study suggests that the greater risk to patients is the loss of the insulating barrier between high-voltage components, particularly between an abraded high-voltage defibrillator cable and the shocking coil or pulse-generator can," Hauser said. His analysis was based on data St Jude had provided to the FDA.
The company had issued a warning letter about the Riata and Riata ST leads to physicians in December 2010, when it pulled them from distribution, and a stronger safety advisory a year later--which the FDA reclassified as a class I recall in December 2011, as covered by heartwire . It had been found that the leads' internal conductor wires could abrade the inside of and erode through their silicone insulation and "externalize." The process appeared to be taking at least a couple of years and up to about six years before causing detectable electrical abnormalities.
Actually, Hauser pointed out, insulation breaches could be caused either by such "inside-out" abrasion or by "outside-in" abrasion, perhaps by lead contact with the pulse-generator can. And while cable externalization from inside-out abrasion is a problem, they don't seem specifically related to the electrical shorts. And insulation failures near other exposed cables or the ICD system's other metal structures "are the manifestation of abrasion that concerns us the most," he said.
Such short circuits were believed to be the cause of 22 deaths in patients with Riata leads in data Hauser presented at the ACC sessions, which appear in different form in a report published almost simultaneously online in Heart Rhythm on March 26, 2012 [1].
"Many of those deaths could not have been predicted; there were no signs," he said. Generally, the "radiographically opaque" shocking coils and generator cans will block fluoroscopy from showing how close they may be to insulation breaches.
In other words, he said when interviewed by heartwire , of the >70 000 patients currently living with Riata leads covered by the recall, just in the US, some of them have insulation failures that are positioned in such a way that they are at risk of causing potentially fatal high-voltage short circuits, "and there may not be a good way of identifying them."
In an email to heartwire , Dr Bruce L Wilkoff (Cleveland Clinic, OH) said, "The inside-out abrasions that can be seen on fluoroscopy do not seem to place the patients at significant risk of electrical dysfunction and, in particular, do not place the patient at risk for shorts between conductors." Wilkoff is one of the world's leading experts on ICD lead dysfunction and revision and is currently president of the Heart Rhythm Society.
"However," he continued, "outside-in abrasions of the can on the lead or one loop of a lead on another lead in the pocket can be associated with a shorting of the high-voltage shock. This is not unique to the Riata, nor is it a new failure mechanism. The rate of this is likely small, but it is important to be aware of when evaluating these patients."
Asked to comment on the Hauser et al report, St Jude referred heartwire to a public response from Dr Mark Carlson (chief medical officer, St Jude Medical Cardiac Rhythm Management) [2]. In it, he says that St Jude's own analysis of the cases in the report suggests that the contentions of Hauser et al "are not entirely accurate." He also refers to the MAUDE database's "lack of information and reliability."
Hauser, in his ACC presentation and in the published report, acknowledged that the database is incomplete and has other limitations.
Bellwether in Belfast?
With cable externalizations the focus of the January Riata lead summit, a group from Northern Ireland presented data on 165 patients there who had received the problematic Riata leads and were invited to undergo fluoroscopic screening in 2010. Externalized conductors were identified in 15%.
Here at the ACC sessions, the same group's Dr Emily Hodkinson (Royal Victoria Hospital, Belfast, Northern Ireland) reported on a new round of screening in 2011 on 147 patients with the leads (of 212 invited), many of whom had been in the previous year's cohort.
The group identified seven cases of cable externalization at fluoroscopy, including three cases in patients who in 2010 had not shown such problems, two cases in patients who in 2010 had been "borderline" for possible cable externalizations, and two new cases in patients not screened in 2010.
But in the entire 2011 cohort, "all system checks were normal." That is, no abnormalities were seen in pacing thresholds, battery voltage, impedance, over- or undersensing, or other electrical parameters.
In an analysis of cumulative lead failures covering both years, significant predictors included longer duration of lead implant (p=0.001), younger age at implant (p=0.002), and lead diameter, in that the 8F Riata leads had a higher failure rate than the 7F Riata ST leads (p=0.003).
Hodkinson said the calculated failure rate for 8F leads was one per 14.7 patient-years and one per 58.6 patient-years for 7F leads (8F vs 7F hazard ratio 4.3; 95% CI 1.6–11.2).
Hauser's presentation at the ACC sessions focused on 105 Riata and Riata ST leads that had been returned to St Jude and found to have 222 insulation defects from abrasion and that were reported to FDA via the Manufacturer and User Facility Device Experience (MAUDE) database. Of those, 143 were from inside-out abrasion, 34 were from outside-in abrasion, and 36 were from the generator can.
Of the 105 leads, 27% had inside-out abrasions in positions underneath at least one of the shocking coils. The exposed cables had melted in six of the leads, "presumably the result of high-voltage short circuits," Hauser said. And 30% of them were associated with inappropriate shocks.
There were 22 deaths considered lead-related, 18 of them in Riata leads and four in Riata ST leads; high-voltage short circuits associated with can abrasions were the cause of death in seven cases.
"As this whole Riata story unfolds, clearly we need more data on how to evaluate these patients," Hauser said after his presentation. Physicians should be routinely sending explanted failed leads to the manufacturer along with the data on electrical performance, and "certainly they all need to be on remote monitoring."
During the question-and-answer period, Dr Claudio D Schuger (Henry Ford Hospital, Detroit, MI) rose from the audience to highlight Hauser's points in his own center's experience, where they are seeing Riata cable externalizations by fluoroscopy "with increasing frequency." But he also described a case of a nonfatal high-voltage short between a Riata lead and one of the defibrillation coils. Measurements of lead impedance before and after the event showed no abnormalities, nor did fluoroscopy. The patient declined to have the leads extracted.
But the case, he said, underscores that "you cannot rely on noninvasive impedance measurements to assess the integrity of what will happen in a high-current short situation. And given that, recommendations about how to follow these leads from the point of view of noninvasive interrogations and remote [monitoring] become a bit unnerving."
Hauser replied, "Yes, unfortunately we're confronted with a situation where we may not be able to predict that there is a lead problem, and the first event may be what happened to your patient."
Hauser has previously had no relevant disclosures.Wilkoff receives no income from any manufacturer of medical devices or drugs. He is on the lead advisory board to review device performance for St Jude Medical.
Heartwire from Medscape © 2012 Medscape, LLC
Cite this: Riata ICD Lead Failures: Focus Shifts to Short-Circuit Risk - Medscape - Mar 30, 2012.
