Subcutaneous ICD system found to be safe, effective

A subcutaneous implantable cardioverter-defibrillator (S-ICD) that purportedly minimizes lead complications is safe to use and is effective at stopping episodes of ventricular tachycardia (VT)/ventricular fibrillation (VF), according to a study published in the Aug. 27 issue of Circulation.

Serious problems associated with transvenous devices include the dislodgement of leads, pneumothorax, pericardial effusion and cardiac tamponade. “The long-term complications associated with the transvenous ICD leads have been a rationale to develop a totally [S-ICD],” the researchers wrote.

The investigators, led by Raul Weiss, MD, of The Ohio State University in Columbus, tested the S-ICD System (Cameron Health), which is FDA-approved but not yet widely used. The system delivers shocks of 80 joules and takes about 20 second to deliver it.

They conducted a prospective, nonrandomized trial at multiple institutions and enrolled 330 patients who needed an ICD and received the S-ICD. At the end of the study period, 293 participants remained. The researchers followed them for an average of 11 months and followed up at 30, 90 and 180 days after S-ICD implantation.

The primary endpoints measured complications at the end of 180 days after implantation and determined the acute induced VF conversion rate at the time of implantation compared with a performance goal of 88 percent. They considered the device successful if there were two VF conversions in four attempts.

Complications were defined as any adverse outcomes that required invasive measures and were broken into four categories. Type 1 complications were caused by the S-ICD System and were the ones included in the safety endpoint.

“Both primary endpoints were met: The 180-day complication-free rate was 99 percent, and sensitivity analysis of the acute ventricular fibrillation conversion rate was [more than] 90 percent in the entire cohort,” the authors wrote.

Any complications that did occur, they noted, “were manageable without invasive intervention in the majority of cases.”

VT/VF occurred in 21 patients, and all 119 episodes were successfully converted. There were 41 patients who were shocked inappropriately.

They also noted that 13 percent of the patients in the study had a transvenous ICD that had to be removed because of complications such as infection, clots or lead failure.

Although there was no control group, “[t]he results of the present study indicate that the subcutaneous implantable cardioverter-defibrillator is a viable alternative to transvenous systems among patients who do not require pacing therapy for heart failure, bradycardia or ventricular tachycardia,” the authors wrote.

Leslie A. Saxon, MD, of the University of Southern California Keck School of Medicine in Los Angeles, wrote in an editorial that despite the study’s findings, the S-ICD System has some disadvantages, such as the lack of remote monitoring and a longer defibrillation time than transvenous devices, that need to be worked out.

There are also some unknowns—Saxon touched on how long the device will last and what safety advisories are warranted—that also need to be addressed.

“In the best of all possible worlds, the subcutaneous ICD will grow and evolve into a device whose design supports the growth of features and capabilities that can evolve with the patient’s condition,” she wrote.

The S-ICD System Investigational Device Exemption Clinical Study was sponsored in its entirety by Cameron Health, a subsidiary of Boston Scientific. The study investigators are consultants for or have received research support from either company. The editorialist is a medical adviser for Boston Scientific.