Riata Revelations: ICD Lead Failure Rates, Mechanisms Take HRS Center Stage

May 11, 2012

May 11, 2012 (Boston, Massachusetts) — If standing-room-only crowds are a sign of stardom, then the discontinued Riata line of implantable defibrillator leads (St Jude Medical) is a main headliner at the Heart Rhythm Society 2012 Scientific Sessions. Research groups lined up to report their experiences with the leads, officially "recalled" in December 2011 because of a high risk of failure, throughout the meeting, in a heavily attended morning session, a highly promoted "late-breaking trial," and abstract after abstract. It's a collective effort to define what isn't yet actually known: the nature and scope of the problem.

The conductor wires inside Riata lead and perhaps its cousin Riata ST, as heartwire has been reporting for months, can erode through their silicone insulation and "externalize," sometimes causing electrical abnormalities, lead malfunction, or possibly high-voltage shorts. And in a controversial published report, such shorts involving Riata leads were thought to be the cause of 22 patient deaths.

But Dr Laurence M Epstein (Brigham and Women's Hospital, Boston) cautioned against focusing too much on the externalized cables as the source of Riata malfunctions. "In my mind, cables that externalize, which people have called a cosmetic problem, are a lead failure. It's not how the lead was designed to function," he told heartwire . But the leads show electrical abnormalities even without the externalizations. "One of the concerns I have is that we don't fully understand the mechanism of why these leads are failing, and I think that's really important for us to understand moving ahead."

At one of the meeting's higher-profile Riata sessions, Dr Raed H Abdelhadi (Minneapolis Heart Institute, MN) reported a failure rate of 1.93% per patient-year for the Riata lead in the Independent Multicenter Riata Study. For the Riata ST lead, the rate was only 0.5% per patient year, which was similar to a rate observed for Quattro Secure leads (Medtronic) in the literature, used in this study as a comparator.

Among the findings of their retrospective analysis, Abdelhadi said, were that conductor externalizations were a common occurrence with the leads, as were impedance and threshold changes, and that oversensing was often a sign of Riata failure and frequently led to delivery of inappropriate therapy.

The study looked at 1081 patients who received Riata and Riata ST leads at seven centers from 2002 to 2010, three-fourths of them with primary-prevention implantable cardioverter defibrillators (ICDs). Of the 1081 patients, 774 received 8F Riata leads and were followed an average of 4.2 years; 307 received 7F Riata ST leads and were followed a mean 3.3 years.

Overall, the all-cause rate of lead failure was 6.2%, with failure defined as abnormal impedance or elevated pacing thresholds prompting lead replacement, "electrical noise manifesting as nonphysiologic signals," cable externalization as visualized on fluoroscopy or X-ray "even if the lead was functioning normally and electrically intact," and "inability to provide effective therapy due to an apparent lead abnormality," according to Abdelhadi.

Failure rates (in % per patient-year) for Riata and Riata ST in the Independent Multicenter Riata Study, vs Quattro

Parameter Riata, n=774 Riata ST, n=307 Quattro, n=1668
Mean follow-up (y) 4.15 3.26 3.18
All cause failure (%/patient-y) 1.93a 0.50 0.43
Electrical malfunction (%/patient-y) 1.34b 0.40 0.43

a p < 0.0001 vs Quattro and p=0.063 vs Riata ST

b p=0.0003 vs Quattro and p=0.018 vs Riata ST

There were 27 cases of externalized conductors, but only seven of them showed evidence of electrical malfunction. Of the 47 cases of electrical malfunction, 25 consisted of electrical "noise" and 11 of those were associated with delivery of inappropriate therapy.

One goal of the study was discovery of predictors of Riata failure, Abdelhadi said, but none could be identified. Failure was apparently unrelated to patient age or sex, ICD indication, the primary heart disease, LVEF, or lead tip position.

Speaking with heartwire , Dr Hugh Calkins (Johns Hopkins University, Baltimore, MD), who wasn't involved in the study, said its findings will help form a basis for estimating failure rates for the Riata and Riata ST. "I think this study was largely confirmatory of what we knew and expected — there is a high rate of failure," and many other Riata presentations are coming up with similar numbers, he observed.

"I think many of the people in the world who are actively focused on this [issue] are here at this meeting, so hopefully as a result there will be a much greater sense of how to move forward than before we all came together."

Abdelhadi, Epstein, and Calkins had no disclosures.


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