Subcutaneous ICD Offers Viable Option for a Number of Patient Populations

Feb 03, 2014 at 04:31 pm by Staff

For nearly three decades, many patients with arrhythmias or at high risk for sudden cardiac arrest (SCA) have benefited from implantable cardioverter defibrillators (ICDs), which help regulate the heart’s electrical signaling. For some, however, the traditional ICD poses problems that a new subcutaneous iteration avoids while still effectively treating ventricular tachyarrhythmias. Sharon Shen, MD, an electrophysiologist with Vanderbilt Heart, explained the difference between the traditional system and the new subcutaneous system (S-ICD). “The subcutaneous ICD doesn’t have any transvenous leads,” Shen said. “Instead of the generator sitting under the collarbone, it sits on the left lateral chest wall. From there, the defibrillator lead travels underneath the skin across the chest and goes up along the left of the sternum.” She added, “The benefit of this system is it’s outside the chest wall so there are no components inside the vascular system or inside the heart.”Shen, an assistant professor of Medicine at Vanderbilt, said the different routing for the leads avoids the acute complications that can come with transvenous placement, including myocardial perforation, pericardial tamponade, venous thrombosis and pneumothorax. “When these leads have been in the vascular system and the heart for a long time, there is the potential for occlusion of those veins, risk of infection in the veins, and potentially infection in the heart,” she noted.Another consideration is lead failure. In younger patients, individuals can easily outlive the longevity of the leads. When that happens, the intravascular leads can be difficult to extract and replace since fibrosis tends to occur over time.Shen, who came to Vanderbilt from Northwestern University, worked with the Cameron Health subcutaneous device (now part of Boston Scientific) during the clinical trial phase in 2010 and 2011. The device, which has been routinely used in Europe for several years, received FDA approval for use in the United States in late September 2012. Currently, Shen said, Vanderbilt is the only site in Tennessee offering this technology.She noted, “It is FDA approved for anyone who is a candidate for a defibrillator including primary and secondary prevention indications.” However, she continued, “A transvenous defibrillator also has pacing capabilities. This device does not … its sole function is to shock patients out of dangerous arrhythmias.” She added, “If you need chronic resynchronization therapy, this would not be the device for you.”It might, however, be just the device for several patient populations. “There is a group of patients that just don’t have the venous access to allow the standard ICD,” Shen noted. Others who could benefit from S-ICD, she added, are those who have already experienced lead failure or infection with traditional ICD, younger patients with primary electrical problems who could potentially face lead issues over the long haul, and those with congenital heart abnormalities that preclude implantation of a standard transvenous defibrillator. Patients with renal failure, Shen noted, are another candidate group. With the ongoing potential for introducing bacteria into the bloodstream during dialysis, the S-ICD might help mitigate infection risk since the subcutaneous leads leave the heart and vasculature untouched. Instead of counting beats, the S-ICD uses a sensing algorithm to analyze the heart rhythm and deliver defibrillation when ventricular tachyarrhythmias are detected. Shen said S-ICD reads the heart more like an EKG would. In some small studies, there is evidence that because the S-ICD “sees” the rhythm rather than just counting how fast the beat is, it might actually help patients avoid unnecessary shocks by effectively discriminating AF and SVT from the more dangerous VT/VF. However, Shen said more research with a larger study population would be required to fully establish that advantage.Like traditional ICD, the subcutaneous system is programmable as a single or dual zone device to tailor therapy to the patient’s needs. Unlike the transvenous method, the S-ICD can be implanted using only anatomical landmarks, which eliminates the need for fluoroscopy during implant thus reducing radiation exposure for both patients and physicians.    Although the subcutaneous procedure is less invasive than the traditional method, the generator used with S-ICD is actually a little larger. Yet, many patients still prefer it from a cosmetic standpoint because the pulse generator is implanted on the side of the chest near the armpit, making it easier to hide in clothing. Shen said the traditional ICD generator, located near the collarbone, is more noticeable when wearing an open-neck shirt or dress.“The studies so far show it (S-ICD) has equal efficacy in shocking people out of dangerous rhythms,” Shen said. However, she added, this is still a new device and therefore doesn’t have the same duration of follow-up as traditional implantation, which has been used since the 1980s.“I don’t see this as a replacement for the transvenous ICD,” Shen continued, “but I see it as an addition to what we can offer our medically complex patients … I see it as a tool to customize care for our patients.”

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