11% of Riata leads externalized in Danish study

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 - electrical shock, ICD shock

A study of all Danish survivors with implanted recalled Riata implantable cardioverter-defibrillator (ICD) leads found that 11 percent of the leads had externalized. The study also found an association between the degree of externalization and time since implantation, and an association between the location of the externalization and the number of coils. These findings were published online Feb. 15 in HeartRhythm.

The FDA recalled 8 French (8F) and 7F Riata ICD leads (St. Jude Medical) in November 2011, due to insulation defects leading to externalization of high-voltage and low-voltage conductors. 

In March 2012, Jacob M. Larsen, MD, of Aalborg University Hospital in Denmark, and colleagues, located all 299 Danish survivors with implanted Riata ICD leads using the Danish Pacemaker and ICD Register. The researchers reviewed the records of previous device interrogations. They noted pacing threshold, R-wave sensing, pacing impedance and high-voltage lead impedance at last measurement before discharge after implantation and most recent follow-up. All but one of the patients underwent screening fluoroscopy to examine the Riata leads.  

Fluoroscopy showed that 11 percent of the leads had externalized, with a median time since implantation of 5.1 years. More 8F leads were externalized (21 percent) than 7F leads (6 percent), but the 8F leads also had a longer median time since implantation (6.4 years vs. 4.5 years). The largest multicenter study of Riata lead externalization to date found a higher rate of externalization (14.3 percent) at a longer interval since implantation (63 months) (Circ Arrhythm Electrophysiol 2012;5:809-814).  

All of the externalizations, with one exception, were located in the distal and intermediate intra-cardiac zones. Patients with dual coil leads more often experienced externalization in the distal zone below the tricuspid valve annulus than did patients with single coil leads. Two patients had two unconnected externalizations in separate zones. There was no association between the size of the leads and the location of the observed externalizations.

Electrical abnormalities occurred at the same rate, 6 percent, in patients with and without externalization. The researchers noted that as most externalizations are electrically silent, x-ray or fluoroscopy is necessary to identify externalized leads.

They pointed out that their findings that externalization is time-dependent supports lead extraction, especially for young patients: “[E]xtraction may be even more challenging if the extent of externalization progresses during watchful waiting,” the authors wrote.  They recommended prospective studies with fluoroscopy to assess the long-term performance of the recalled leads.

Larsen et al did not find that externalization was associated with electrical failure, and they attributed this to survivor bias, which they acknowledged was a limitation of their study. They also noted that their diagnoses of lead externalization by fluoroscopy were not confirmed by lead extraction, and therefore there may be some risk of misclassification.