Conventional implantable cardioverter-defibrillators (ICDs), an established therapy for the prevention of death from ventricular arrhythmia, rely on transvenous leads for cardiac sensing and defibrillation. Complications of implantation have been mainly associated with transvenous lead insertion, and once in place, lead failure can generate inappropriate shocks, or impede appropriate therapy. Removing failed leads is also associated with substantial morbidity and mortality. There may be an advantage to avoiding the use of transvenous leads, making the possibility of an entirely subcutaneous ICD an appealing alternative for certain patients.
Bardy et al. first evaluated an entirely subcutaneous ICD in two short-term trials to identify a suitable device configuration and assess energy requirements. In a six-patient long-term pilot study and a 55-patient single-arm trial, the subcutaneous cardioverter-defibrillator consistently detected and converted induced ventricular fibrillation, and detected and treated all of 12 spontaneous ventricular tachyarrhythmias.
“While further study in a large, randomized clinical trial is needed before subcutaneous ICDs are used, these results are interesting, and there may soon be options for some patients,” says John Jarcho, M.D., NEJM deputy editor.
Many ICDs distinguish between ventricular fibrillation and ventricular tachycardia, and try to terminate the tachycardia through pacing before it progresses to ventricular fibrillation. For those patients who benefit from such cardiac pacing, the subcutaneous ICD tested in this study could be considered a less viable option, as it is not capable of terminating ventricular tachycardia by pacing. It is also not able to provide backup antibradycardia pacing for those patients who may need it.
The authors note, “The goal of developing subcutaneous ICDs was to overcome some of the problems that are associated with transvenous leads in conventional ICDs….These benefits would be especially important for young patients in whom leads may fail during the decades that therapy is needed.”
How frequently do your patients benefit from an ICD device that also provides cardiac pacing? Based on these results, are you encouraged that some of your patients may soon benefit from a subcutaneous ICD?