Canadian Riata Experience: Electrical Failures Eclipse Externalized Cables

January 24, 2013

WASHINGTON DC — A snapshot of Riata (St Jude Medical) implantable defibrillator lead performance in Canada as of March of last year finds a 4.6% overall rate of electrical failure over a median of five years [1]. Electrical failure, significantly more common with the Riata model than with Riata ST leads, was usually due to impedance changes, oversensing due to noise, and elevated pacing capture thresholds.

The findings come from a survey of 21 Riata sites across Canada performed by the Canadian Heart Rhythm Society (CHRS) and published online in Heart Rhythm on January 21, 2013. Riata leads, as heartwire has long covered, were "recalled" by the US FDA in December 2011 but under scrutiny for at least the previous year for a higher-than-expected failure rate.

Adding intrigue to the saga, the leads are prone to a unique form of structural failure in which the lead's internal cables work their way through the insulation to the outside. The externalized cables may or may not be associated with electrical abnormalities, and the latter can occur without insulation failure.

In the current series of 4358 leads, reported by Dr Ratika Parkash (Queen Elizabeth II Health Sciences Centre, Halifax, NS) and associates, about two-thirds were the 8 F Riata and one-third the 7 F Riata ST.

The overall rate of electrical failure was 4.6%, but it was significantly higher in Riata (5.2%) than in Riata ST leads (3.3%) (p=0.007). However, Riata leads have, on average, been in patients longer as the model was introduced before the Riata ST.

"The most common electrical abnormalities observed were a sudden rise in pacing capture threshold (43.8%), a change in impedance (29.9%), or oversensing of noise (23.9%)," according to the report.

Externalized cables were observed in only 8% of all leads with electrical failure. The authors note, however, that data on externalizations were not routinely available from the centers.

"One of the most significant unanswered questions is the mode of failure of the Riata lead and how the structural abnormality of cable externalization relates to this. From our study and others, it is clear that there is a rate of electrical failure that is distinct from structural failure," the group writes.

On the other hand, that so few of the electrically failed leads also showed externalization by radiography may be an underestimation "due to a lack of systematic radiographic screening at the time of this study in Canada."

The analysis was supported by a research grant from St Jude Medical. Parkash reports receiving research grants from St Jude, Medtronic Canada, and Bayer Pharma. Disclosures for the coauthors are listed in the paper.