S-ICD, Sans Bells and Whistles, a "Viable Alternative" in Some ICD Candidates

August 28, 2013

DALLAS, TX - Unique on the market, the S-ICD (Cameron Health/Boston Scientific), an implantable cardioverter-defibrillator (ICD) with a totally subcutaneous lead system, was judged "safe, well-tolerated, and effective" in a large, international prospective series of primary- and secondary-prevention patients[1].

As the device lacks antitachycardia pacing (ATP), those with a documented history of ventricular tachycardia that had been "reliably terminated" with ATP were excluded from the >300-patient cohort; the S-ICD does provide temporary backup pacing for postshock bradycardia.

"The S-ICD system is effective at detecting and treating both induced and spontaneous VT/VF," according to Dr Raul Weiss (Ohio State University, Columbus) and associates. "In this study, there were no instances of acute complications associated with the use of transvenous lead insertion, such as pericardial effusion, cardiac tamponade, cardiac perforation, hemothorax, or pneumothorax."

Notably, there were no reported cases of device-related endocarditis, which can frequently follow device-related infection and increases mortality risk, the group observes in the August 27, 2013 issue of Circulation. "The S-ICD system represents a viable alternative to conventional ICD therapy in patients at risk of death from VT/VF."

Identified on clinicaltrials.gov as the S-ICD System IDE Clinical Study , the prospective series and its results, before their publication, convinced an FDA advisory panel majority and the agency itself that the system should be approved. That happened in September 2012, as reported by heartwire .

"One Essential Meaning, Purpose, and Value"

The "largely defeatured" S-ICD generator is larger and heavier than a transvenous-ICD generator, and as with the first ICDs to become available decades ago, "is pared down to one essential meaning, purpose, and value: ventricular arrhythmia defibrillation," writes Dr Leslie A Saxon (University of Southern California, Los Angeles) in an accompanying editorial[2].

"The parasternal subcutaneous ICD defibrillating lead does not require fluoroscopy to implant, but proper placement of the parasternal lead and chest-wall pulse generator requires new surgical techniques that were associated with acceptable risk in this study. Because the system was designed to overcome the complications and failures associated with transvenous implants, it does achieve those goals."

On the other hand, "Other acute and chronic complications associated with implanted ICD pulse generators and ICD systems, such as infection and the need for wound revision, were not decreased significantly with this system in comparison with the transvenous pulse generators." Nor were there fewer inappropriate shocks.

Still, she writes, "This ICD poses a significant existential crisis for the now–middle-aged standard, transvenous, and fully featured ICD."

Co–Primary End Points Met

Of 330 enrolled patients, 314 were successfully implanted with the S-ICD system; eight out of 10 patients had a primary-prevention indication. Three-quarters were men, and 13% had previously been implanted with a transvenous system.

Over an average follow-up of 11 months (mean and median), the primary safety end point of freedom from complications at 180 days was reached by 99% of patients, "well above the [prespecified] performance goal of 79%." The primary effectiveness end point, conversion rate of induced VF, was 100% excluding patients without evaluable electrophysiologic tests and 94.7% when those patients were included; the prespecified performance goal was 88%.

Also:

  • All 38 discrete spontaneous VT/VF episodes (22 monomorphic VT and 16 polymorphic VT or VF), recorded in 21 patients, successfully converted with 43 appropriate shocks.

  • Inappropriate shocks occurred in 41 patients.

  • There were 18 suspected or confirmed infections.

  • Postshock pacing (the system can pace in demand mode at 50 pulses per minute for up to 30 seconds) engaged appropriately all 184 times the intrinsic heart rate went below 50 bpm and was inhibited whenever the intrinsic rate exceeded 50 bpm, except in one instance out of 544.

  • Of the eight patients who died (2.5%), "five were noncardiac, nonsudden, and unrelated to the implantation procedure."

Although the S-ICD effectiveness data "are reassuring and comparable to transvenous ICD success rates, the overall number of treated episodes is incredibly small in comparison with the data on transvenous defibrillator therapies delivered outside the hospital, over the life of the device, that are available for analysis in tens of thousands of patients," writes Saxon in her editorial.

The study was funded by Cameron Health, a Boston Scientific subsidiary. Weiss reports being a consultant for or receiving honoraria and research support from Cameron Health and Boston Scientific. Disclosures for the coauthors are listed in the paper. Saxon discloses being on Boston Scientific's medical advisory board and receiving research funds from Boston Scientific, Medtronic, and St Jude Medical, and to being principal investigator at her center for the S-ICD System Safety and Effectiveness Study.

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