Canadian survey places Riata electrical failures at 4.6%

A survey of two Riata lead models under advisory in Canada found that 4.6 percent of the leads had confirmed or suspected electrical failure. HeartRhythm published the results online Jan. 21.

St. Jude Medical issued an advisory Nov. 28, 2011, about estimated failures related to its Riata (8Fr) and Riata ST (7Fr) silicone endocardial defibrillation leads. The company reported that the estimated worldwide rate of all-cause abrasion increased from 0.47 percent in December 2010 to 0.63 percent in November 2011. About 15 percent exhibited externalized conductors possibly due to an inside-out abrasion mechanism.

“The implications of this novel mechanism of lead failure are concerning, due to the possibility of abnormal electrical conductance if a faulty lead is left in place, and interacts with another ICD [implantable cardioverter-defibrillator] lead, potentially causing further abrasion with this lead,” wrote Ratika Parkash, MD, of the QEII Health Sciences Centre in Halifax, Nova Scotia, and colleagues in their introduction.

To assess lead revisions after issuance of the advisory, the researchers designed and sent a survey to 19 Canadian centers that implant ICDs and two follow-up centers, all sites that participate in the Canadian Heart Rhythm Society’s device committee.

Through the survey, they collected data on the Riata (8Fr) models 1560, 1561, 1562, 1570, 1571, 1572, 1580, 1581, 1582, 1590, 1591, 1592; and Riata ST (7Fr) models 7000, 7001, 7002, 7010, 7011, 7040, 7041 and 7042.

The survey data captured the number of leads and models implanted at each center; the number of leads revised or found to have electrical lead failure and model number; the number of patients with lead abnormalities and model number; deaths attributed to lead failure; the number of revised leads and model number; and the method of revision and model number.

Parkash et al defined lead failure as a lead that fails to perform its intended function because of a structural or electrical failure and is removed for safety reasons. Structural failure included externalized leads due to abrasion-related issues as seen radiographically.   

The researchers obtained data on 86.4 percent of active leads under advisory in Canada, as of March 2012. They determined that the median time from implant to last follow-up was five years. Most—65.3 percent—were 8Fr models. Based on the survey, there were electrical abnormalities in 4.6 percent of affected leads, and the 8Fr models had significantly higher electrical failures than 7Fr models (5.2 percent vs. 3.3 percent). Externalization was seen in 8 percent of electrical failure cases.

Of the leads with confirmed failures, over-sensing with or without inappropriate shocks occurred in 39.8 percent. There was one death attributed to lead failure due to lead-can abrasion found post-mortem. Most leads were revised by inserting a new lead, and most leads were capped and abandoned. Two major complications were attributed to lead extractions.  

Parkash et al wrote that their results as well as findings from other studies show a higher incidence of failure in both lead models than had been reported using passive surveillance data.

“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,” they wrote. They emphasized that the 8 percent finding of structural abnormalities may be an underestimate because at the time Canada did not require systematic radiographic screening. “This indicates that the fragility of this lead is related to an increased failure rate, but that it goes beyond just the novel inside-out erosion resulting in cable externalization. The importance of other issues that may arise from cable externalization such as thrombus formation, mechanical factors of an externalized cable within the heart remains to be seen.”

Whether lead extraction or lead abandonment is the best course remains unclear, they wrote. Because the study was based on a survey, it was vulnerable to reporting bias and variable interpretations of lead failure. Given the lack of a screening system, their results on electrical and structural failure may be an underestimate due to under-reporting. Nor did they track failure over time, which might affect comparisons between the 7Fr and 8Fr models.

St. Jude Medical provided a research grant for the data analysis in the study.