A new prospective, non randomised, multicentre trial, published in Circulation, has found that the subcutaneous implantable cardioverter defibrillator (S-ICD System, Cameron Health/Boston Scientific) is safe and effective at detecting and treating both induced and spontaneous ventricular tachycardia and ventricular fibrillation in a broad range of patients requiring implantable cardioverter defibrillators (ICDs).
The S-ICD System includes a lead placed under the skin along the left side of the breast bone and was developed as an alternative therapy to avoid the complications perceived with the use transvenous leads with traditional ICDs.
“Defibrillation has repeatedly proven to be a great asset in prolonging the lives of cardiac patients, but there are still some risks to address,” said Martin C Burke, senior author of the study and a professor of medicine and director of the Heart Rhythm Center at the University of Chicago, USA. “This new system was developed over a dozen years to combine some of the best aspects of traditional implanted ICDs and external defibrillators.”
Leslie A Saxon, University of Southern California, USA, wrote in an accompanying editorial: “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.”
In the 33-site S-ICD System IDE clinical study, 314 of 330 patients (average age 52) evaluated had the S-ICD System implanted. During an average 11-month follow-up, 21 patients spontaneously developed 38 episodes of ventricular fibrillation or ventricular tachycardia. All were successfully restored to a normal heart rhythm. In addition, 41 patients (13.1%) received shocks that were inappropriate because they were not preceded by a dangerous heart rhythm.
The study surpassed goals set by the US Food and Drug Administration (FDA) for evaluating the safety and effectiveness of the device:
- Ninety-nine per cent of the S-ICDSystem patients remained free of complications 180 days following implantation, compared with a 79% goal.
- When tested by a purposely-induced abnormal rhythm following implantation, the S-ICD System was 100% effective at consistently detecting and reversing ventricular fibrillation. The FDA goal is 88%.
“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,” wrote Saxon. “Additionally, there was one safety advisory field action on a pulse generator during the conduct of the trial that required explant of the pulse generator. Therefore, it is unclear, until a greater experience is accumulated, if the ICD system, in its entirely, will be associated with a lower safety advisory rate.”
According to the authors, participants in the study, along with new patients, will be followed to assess the performance of the new device over time.
“The S-ICD System is not a replacement for other defibrillators,” Burke said. “For some patients it will be ideal, for others inappropriate, and the vast proportion in the middle will be able to select the type of system they want.”
Saxon wrote: “Selecting the appropriate candidate for the subcutaneous rather than the transvenous ICD requires and acknowledgment of the strengths and limitation of each device and an educated guess, as well, regarding the clinical course of the patient, over the battery life of the ICD.”
“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. This includes integrating wirelessly with other hardware- and software-based healthcare solutions that will enhance the device and the device recipient’s overall medical condition. The enhancements will provide multiple reasons for the subcutaneous ICD to exist,” wrote Saxon.
The authors concluded: “The S-ICD System represents a viable alternative to conventional ICD therapy in patients at risk of death from ventricular tachycardia and ventricular fibrillation”.
A comparison between a traditional ICD and the S-ICD System is underway.
The S-ICD System has been available in Europe and New Zealand since 2009 and received FDA approval in the United States in 2012.