In the latest chapter in the U.S. saga of the subcutaneous implantable cardioverter-defibrillator (S-ICD) system (Boston Scientific) – a large postmarket, multicenter registry study – the device performed at least as well as it did in earlier trials, researchers say.
The device met all prespecified safety and efficacy endpoints in a study that enrolled more than 1,600 patients and followed them for about 5 years, they noted in their report on the S-ICD Post-Approval Study (S-ICD-PAS) published online in the Journal of the American College of Cardiology.
the group reported.
The team was “pleasantly surprised” that the device’s safety and efficacy performance “was as good if not better than previous studies,” despite a sicker group of patients, lead author Michael R. Gold, MD, PhD, Medical University of South Carolina, Charleston, said in an interview.
No predictors of initial-shock failure were identified, suggesting the S-ICD should be effective in a broad range of ICD candidates without indications for pacing, Dr. Gold said.
The S-ICD was approved in Europe in 2008 and by the Food and Drug Administration in 2012. Clinical trials have suggested its performance and risk for inappropriate shocks are in line with transvenous-lead systems for most patients with ICD indications who don’t need pacing, while avoiding the sometimes serious risks posed by transvenous leads.
The S-ICD doesn’t have antitachycardia pacing (ATP), an alternative way to stop some arrhythmias and a universal feature of transvenous-lead systems. Its lack of ATP may be partly responsible for the device’s weak uptake in practice, some observers noted.
The S-ICD-PAS study “laudably included centers with variable prior experience with the S-ICD; however, data were not analyzed by center experience,” Jonathan S. Steinberg, MD, and Valentina Kutyifa, MD, PhD, University of Rochester (N.Y.) Medical Center, New York, wrote in an accompanying editorial regarding the report’s potential limitations.
Also of concern, they wrote, is the large proportion of patients who were lost to follow-up; almost 42% left the study before its prospectively defined end.
Still, wrote Dr. Steinberg and Dr. Kutyifa, S-ICD-PAS “provides robust, long-term evidence in favor of S-ICD use in a diverse cohort of younger patients receiving implants for primary or secondary prevention of sudden arrhythmic death.” Further analyses are needed, however, to clarify its performance “in centers with low vs high volume as well as in important clinical subgroups.”
It’s “reassuring to see the phase 4 postapproval study results sort of corroborate what the initial clinical study shows,” Miguel Leal, MD, Emory University, Atlanta, said in an interview.
The study’s significant attrition rate “does not negate the results because the performance curves of the device remained approximately stable over the 5 years,” he said, “suggesting that the patients who were lost [and whose clinical outcomes were not included] may not have made a significant impact when it comes to the final results.”
Although the S-ICD seems unlikely to cause complications related to endovascular occlusions or infection, “it can still cause complications related to the implant technique, particularly a device site erosion or device dislodgement,” said Dr. Leal, who chairs the American Heart Association Council on Clinical Cardiology–Electrocardiography & Arrhythmia Committee.
The S-ICD’s biggest contribution has been “the ability to promote efficacious therapy without a need for penetrating the endovascular space,” he observed. “We need to continue to push the envelope towards developing device-based technologies that spare the endovascular space.”
The study enrolled 1,643 patients at 86 U.S. centers; their mean age was 53 and 32% were women. Of the total, 1637 were implanted with the device, 665 completed the study, 288 died, and 686 left the study before completing follow-up. Of the latter, 102 (6.2% of the total) underwent S-ICD explantation, often because of infection.
In addition to the overall shock efficacy rate of 98.4%, induced-arrhythmia shock efficacy was 98.7%, first-shock efficacy for spontaneous arrhythmias was 92.2%, and the rate for either induced or spontaneous arrhythmia was 94.7%. A mean of 1.1 shocks was needed to terminate the arrhythmias; time to shock delivery averaged 17.5 seconds.
The rate of inappropriate shocks was 6.7% at 1 year and 15.8% at 5 years, notably with no significant differences between patients who had and had not undergone defibrillation threshold testing at implantation.
Of 516 inappropriate-shock episodes in 224 patients, almost 86% resulted from inappropriate sensing. Inappropriate shocks became less frequent with longer implantation times and during the course of the study.
The rate of freedom from type 1 complications, the primary safety endpoint, was 93.4%, besting the 85% performance goal. The rate of freedom from electrode-related complications was 99.3%, compared with the performance goal of 92.5%.
The S-ICD was replaced by a transvenous system because of the need for pacing in 1.6% of the cohort.
Sana M. Al-Khatib, MD, MHS, who chaired a 2017 multisociety guideline for managing ventricular arrhythmias and prevention of sudden death, acknowledged the 5-year safety and effectiveness of the S-ICD but also highlighted the “very high dropout rate.”
Moreover, given the cohort’s average age, “these results cannot be generalized to much older patients, in their 70s and 80s [for example]. More data on the S-ICD in older patients are needed, especially because some of these patients will need pacing, which is not provided by the S-ICD,” Dr. Al-Khatib, Duke University, Durham, N.C., said in an interview.
Longer follow-up of patients with the S-ICD is also needed, she added, and “having an S-ICD that is smaller with longer battery life would be great for my patients.”
The study was sponsored by Boston Scientific. Dr. Gold reported receiving consulting fees from Boston Scientific and Medtronic and participating in clinical trials with Boston Scientific, Medtronic, and Abbott. Dr. Steinberg, Dr. Kutyifa, Dr. Al-Khatib, and Dr. Leal reported no relevant relationships.
A version of this article first appeared on Medscape.com.