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New data demonstrate efficacy, safety of subcutaneous ICD
The subcutaneous implantable cardioverter defibrillator system appears safe and was well tolerated in a broad range of patients that require implantable cardioverter defibrillator therapy, according to results of a prospective, nonrandomized, multicenter trial.
Complications associated with transvenous leads in traditional ICDs led to the development of a subcutaneous ICD (S-ICD System; Cameron Health/Boston Scientific) that does not touch the heart or vasculature but is placed extrathoracically, Raul Weiss, MD, and colleagues wrote in the study background.
The FDA approved the S-ICD System in September 2012. As a condition of approval, the agency specified goals of 79% of patients remaining free of complications 180 days after implantation and 88% effectiveness at detecting and reversing ventricular fibrillation (VF). Those were the primary endpoints of the study. Those percentages were based on the results of prior ICD studies, Martin C. Burke, DO, professor of medicine and director of the Heart Rhythm Center at University of Chicago, told Cardiology Today.
Martin C. Burke
The researchers enrolled 330 patients, 13% of whom had a previous transvenous ICD, at 33 sites in four countries. Of these, 314 had a subcutaneous ICD implanted successfully. Mean follow-up was 11 months. The study population was 74% men, had a mean age of 52 years and had a mean LV ejection fraction of 36%.
There were 38 episodes of ventricular tachycardia (VT) or VF recorded in 6.7% of patients during the study period, all of which successfully converted. Inappropriate shocks were received by 13.1% of patients. There were eight deaths (2.5%) during the study, five of which were noncardiac.
Goals exceeded
The 180-day device-related complication-free rate was 99%, exceeding the goal of 79%. After the researchers performed a sensitivity analysis incorporating labeling-related and procedure-related complications, the 180-day complication-free rate was 92.1%.
The successful conversion rate was 100%, exceeding the goal of 88%. There were 17 patients who could not be evaluated. If these were counted as failures, the successful conversion rate was 94.7%.
“There had been enough pilot data to suggest that the effectiveness of the device with the shock factor procedural implant technique was very good,” Burke told Cardiology Today. “It was just a matter of expanding it to a larger population with a broader implanting surgeon pool, and then to look at longer-term safety data. … So when we came in at 1% [complication rate] in comparison to [the safety guideline], that was a big surprise.”
No remote monitoring
In a related editorial, Leslie A. Saxon, MD, of the University of Southern California Keck School of Medicine, Los Angeles, said a limitation of the first generation of the subcutaneous ICD is that it does not allow remote monitoring, unlike current versions of transvenous ICDs.
So, she wrote, while “these data are reassuring and comparable to transvenous ICD success rates … without the ability to remotely collect episodes in all subcutaneous device recipients, it is difficult to know how the learning around spontaneous VT/VF episodes will occur, other than the old-fashioned way, through case reports and postapproval registries.
“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,” Saxon wrote.
According to Burke, the subcutaneous ICD is “disruptive, innovative technology, but only in the best way.
“It’s not meant to take away from the value of a transvenous system for certain populations; it’s meant to increase access to populations that may have been biased against getting [the device] because of complications of long-term transvenous lead systems.” Burke said strong candidates for a subcutaneous ICD include those with no venous access to the heart, those with congenital heart disease, those who previously had a transvenous ICD but had problems with it, those at high risk for transvenous infections, and young patients for whom there would be concerns about having a long-term transvenous implant.
For more information:
Saxon LA. Circulation. 2013;128:938-940.
Weiss R. Circulation. 2013;128:944-953.
Disclosure: The study was funded by Cameron Health, a subsidiary of Boston Scientific. All of the researchers have consulted for or received research grants from Cameron Health or Boston Scientific. Saxon is a principal investigator for the S-ICD System Safety and Effectiveness Study, serves on the medical advisory board of Boston Scientific, and has received research funds from Boston Scientific, Medtronic and St. Jude Medical.
Perspective
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We’ve had very little data up until this point regarding the efficacy and safety of the totally subcutaneous ICD. This is a landmark trial that tells us this form of therapy is a feasible alternative for many patients who have standard indications for ICDs that don’t have pacing indications. This is something very new for us. The weakest link of the ICD system is the endocardial lead. There have been lots of problems with failure of leads and complications related to leads. This gives us a great alternative for many patients.
We were involved in the original IDE trial. We had a very favorable experience with implanting the device. There is a little bit of a learning curve in terms of getting to understand that it’s a bit of a different procedure, but after implanting a few devices, you get accustomed to that. We found it easy to implant. Efficacy with converting ventricular fibrillation in the lab was excellent. We also had a favorable experience with follow-up of these devices, without any problems detected.
The device is now approved by the FDA and commercially available. Although the number of patients who receive the totally subcutaneous device at first may start out small, I think adoption rates will increase dramatically once clinicians try it and realize that it works well. It may also potentially reduce complications.
In this study, patients with standard indications for an ICD were eligible for the subcutaneous ICD as long as they did not require bradycardia pacing or antitachycardia pacing. Patients who have the need for bradycardia pacing and patients who have monomorphic ventricular tachycardia that could be pace-turnable should not get this device. It’s a fairly broad indication. Patients must also pass an ECG screening test.
When we first started implanting these devices, we put them in patients who we thought might benefit from not having a lead in their heart, including younger patients who might be very active and patients at higher risk for long-term lead problems. Young patients with a longer life expectancy may require multiple leads throughout their lifetime. As time went on, we realized that this device is also very effective for patients who have sicker hearts and meet standard ICD indications. It is also interesting to note that patients who had a prior infection with an endocardial system and then received a subcutaneous ICD didn’t seem to be reinfected during the period of follow-up. The cohort in the present study was a bit younger than the average age we see in some of other larger ICD trials. However, the study group was otherwise representative of the types of patients we implant ICDs in the United States.
Although not studied here, the totally subcutaneous ICD system could benefit patients who have vascular access issues, such as those with renal failure and arteriovenous fistulas, who are at higher risk for endovascular infection. The other group of patients that I think we should seriously consider for a subcutaneous device are women. There are data to support potential underutilization of devices in women. In the NCDR ICD registry, women receiving standard ICDs had a higher complication rate than men. According to data from the IDE study of the subcutaneous device, there are no gender differences in complication rates, in contrast to endocardial systems. We should certainly consider women as one of the groups to focus on.