August 26th, 2013

New Subcutaneous ICD Said to Pose ‘Existential Crisis’ for Older ICDs

Last year the FDA approved Boston Scientific’s subcutaneous ICD (S-ICD), the first ICD that doesn’t use transvenous leads. Those leads are the source of many sophisticated pacing features in today’s ICDs, but they are also the main source of ICD-related complications.

FDA approval of the S-ICD was based on a pivotal trial designed to assess the device’s safety and effectiveness. Results of the trial have now been published in Circulation. In this nonrandomized trial, the S-ICD was successfully implanted in 314 patients out of 321 in whom the implantation was attempted.

The S-ICD easily met the prespecified primary safety and efficacy endpoints:

  • Primary safety end point (180-day complication-free rate): 99%. The lower confidence limit of 87.9% surpassed the prespecified performance goal of 79%.
  • Primary effectiveness end point (the acute induced VF conversion rate at the time of implantation): 100%, achieved in all of the 304 patients who underwent the full testing protocol, “far exceeding” the performance goal of 88%. A total of 17 patients were not evaluated for effectiveness, but even if all were deemed failures, the acute VF conversion rate would still have been well above the lower confidence limit.

During the course of followup there were 38 episodes of VT/VF in 21 patients. These were all successfully converted. Overall, 13.1% of patients received an inappropriate shock.

The results, write the authors, “demonstrate that the S-ICD System is safe and well tolerated as a chronically implanted ICD and is effective in terminating both induced and spontaneous VT/VF.”

In an accompanying editorial, Leslie Saxon writes that the appearance of the S-ICD “poses a significant existential crisis for the now middle-aged standard, transvenous, and fully featured ICD.” The S-ICD “is pared down to 1 essential meaning, purpose, and value: ventricular arrhythmia defibrillation.”

Although the available data on the S-ICD “are reassuring and comparable to transvenous ICD success rates,” she notes that “the overall number of treated episodes is incredibly small in comparison” with standard ICDs, which also have much longer followup data. In addition, “a significant limitation from a clinical learning and safety advisory perspective” is the lack of remote monitoring capability.

Saxon nevertheless suggests that a “significant percentage” of potential ICD patients may be candidates for the S-ICD, including those with “prohibitive vascular access issues” and those at high risk for major infection associated with a transvenous lead.

In an interview, Saxon said that although the S-ICD is a genuine advance in defibrillation technology, it also represents something of a throwback, as it appears to contradict “the constant evolutionary course of technology” in which more features and capabilities are packed into increasingly small spaces with each subsequent generation of technology.


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