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An Entirely Subcutaneous ICD

Patients at risk for dangerous arrhythmias and sudden cardiac death have long relied on transvenous implantable cardioverter-defibrillators (ICDs) to detect an abnormal heart rhythm and deliver a shock to restore a normal heart beat. Although the ICD has saved many lives, its leads, which are connected to the heart’s chambers, can fail or otherwise lead to serious complications. According to Michael R. Gold, M.D., Ph.D., Director of the Division of Adult Cardiology and Michael E. Assey Chair of Cardiology at MUSC, “Leads are placed inside the heart with the heart beating several million times a year, resulting in a high rate of leads wearing out, fracturing and becoming seriously infected. Within five to ten years, at least 20% of leads will fail.”

The subcutaneous ICD (S-ICD System®; Boston Scientific, Natick, MA) is the first ICD in which the leads are placed under the skin of the chest and are not connected to the heart (Figure). It was approved on September 28, 2012, by the US Food and Drug Administration (FDA) for select patients following the demonstration of the safety and efficacy of the device.1 Dr. Gold was one of the lead investigators presenting data supporting the efficacy and safety of the S-ICD to the FDA panel. Although the distance of the lead from the heart initially raised concerns that it might fail to detect dangerous heart arrhythmias or misinterpret extracardiac signals that would cause it to deliver unnecessary shocks, the START trial (Subcutaneous vs Transvenous Arrhythmia Recognition Testing; Clinical Trial Registration: NCT01161589), for which Dr. Gold served as a principal investigator, provided evidence that, though both types of ICDs (traditional and subcutaneous) accurately detected ventricular arrhythmias, S-ICDs detected supraventricular arrhythmias with more accuracy than did traditional ICDs.2 No lead failures have occurred in the more than 1000 S-ICDs implanted worldwide.

The relative ease with which the S-ICD is implanted and accessed offers a number of safety advantages. Because it is not implanted in the bloodstream, the S-ICD is less likely to lead to vascular damage or to systemic infection than the traditional ICD; when infections do occur, they are typically localized and can be treated effectively with antibiotics. Fluoroscopy is not required to guide S-ICD placement, sparing the patient exposure to radiation. Subcutaneous leads are not subject to the stresses of the cardiac contraction and so are much less likely to fail or need replacement. Should they fail, they are far easier to access and to extract with far less risk of morbidity and mortality for the patient.

S-ICDs are particularly appropriate for younger patients and those with previous infections. For these patients, who may require an ICD for decades to come, the risk of lead failure and lead extraction, which carry significant morbidity and mortality, is much higher when implanted with a traditional ICD, subject to the stresses of the cardiac environment, than with the more durable S-ICD.

S-ICD is also a good choice for chronic renal failure patients, because it spares them the risk of vascular damage that can occur with transvenous ICDs and thus does not threaten venous access for future dialysis. Patients with congenital heart disease, previous cardiac surgery, or certain anatomic constraints that could obstruct placement of a transvenous ICD are also good candidates.

Despite its many advantages, the S-ICD has a number of limitations and so is not appropriate therapy for many patients requiring ICDs. Because it provides no significant pacing support and, unlike the traditional ICD, cannot be used in combination with biventricular pacing, the S-ICD is not recommended for patients with congestive heart failure who would benefit from pacing. The S-ICD also offers no anti-tachycardia pacing, which has been shown to terminate monomorphic ventricular tachycardia without resorting to shock, and so is not the best choice for patients with this condition.

The S-ICD will be rolled out first to medical centers like MUSC that participated in the clinical trials. MUSC is among the first hospitals in the country and the first in South Carolina to offer this next generation of ICD technology to patients. According to Dr. Gold, “S-ICD provides South Carolinians access to the latest technology to help combat sudden cardiac arrest.”

References

¹ Weiss R, Knight BP, MD, Gold, MR, et al. The safety and efficacy of a totally subcutaneous implantable-defibrillator. Circulation 2013 Aug 27;128(9):944-953.

² Gold MR, Theuns DA, Knight BP, et al. Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: the START study. Journal of Cardiovascular Electrophysiology 2012; 23(4): 359-366.

This article originally appeared in the November 2013 issue of Progressnotes.