The Beauty of Subcutaneous ICDs Is Not Merely Skin Deep

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 - ICD

Three decades and 1 million-plus implantations after its introduction, the transvenous implantable cardioverter-defibrillator (T-ICD) is facing stiff competition from a smaller, thinner, more versatile and longer lasting addition to the family tree of implantable devices that shock the heart to prevent sudden cardiac death. The new kid on the branch is the subcutaneous implantable cardioverter-defibrillator (S-ICD). After proving safe, efficacious and not prone to complications in clinical trials, and so earning first FDA approval in 2012, wireless pacemakers today are rising in popularity as the right choice for many patients and preferable to many of the physicians who treat them.

Apart from its diminutive, less intrusive physical profile, one of the S-ICD’s main points of appeal is its placement. While the transvenous implantation requires leads inserted through veins and into hearts, with all the risks such a high level of invasiveness can bring—not to mention the literal beating that leads take inside the heart—the S-ICD uses a lead that does its job under the skin, along the bottom of the ribcage and breastbone. Wireless leaves the heart and vasculature untouched.

More specifically, the S-ICD delivers electric shocks, as needed, by way of a pulse generator implanted in the left lateral chest in combination with a lead-electrode “tunneled” 1 to 2 centimeters to the left of the mid-sternal line. The main rap against it so far is that, unlike the T-ICD, it doesn’t regulate pacing for either fast-heartbeat arrhythmias (tachycardia) or slow ones (bradycardia). But a quick review of the literature shows that, even there, it may come out a winner: Conversations are underway to consider outfitting the S-ICD with Bluetooth radio-wave technology for various pacing purposes.

Meanwhile, newly pooled data on the smaller device point to low mortality, a low or flat complication rate over time and no evidence of problematic implantations, says Martin Burke, DO, director of the Heart Rhythm Center at the University of Chicago. Pointing to an analysis he led of two-year results gleaned from two large prospective studies, publishing the results in the Journal of the American College of Cardiology this past spring, Burke told Cardiovascular Business that the device’s rate of spontaneous event conversion (from arrhythmic to a normal heart rhythm) is “outstanding. It’s comparable to a transvenous system,” which successfully positions it for “non-niche patients at primary prevention or secondary prevention who have no pacing indication. The process of selection now becomes a personal one between physician and patient, with multiple options to choose from.”

Burke and colleagues’ pooled-data analysis (J Am Coll Cardiol 2015;65:1605-15) showed termination of 90.1 percent of ventricular tachyarrhythmia and ventricular fibrillation events after one shock, with some 98.2 percent halted after up to five shocks from the S-ICD.

Numbers like those, coupled with similarly encouraging data on safety and complications—on top of longer battery life and remote follow-up capabilities—are “going to let these devices rule the day for just about anybody who’s at risk for sudden cardiac death and who doesn’t have any pacing indications,” says Burke, who consults for Boston Scientific. (The company’s Emblem S-ICD has CE Mark approval for sales in Europe, and the FDA greenlighted a second-generation version earlier this year.)

“The other thing is, with [the S-ICD’s] longer detection times, we’re seeing a low need for shocking in general,” adds Burke. “We’re seeing the device actually not go off, because the charge time takes longer to occur so that the event spontaneously terminates. We’ve seen this now in greater than 50% of all the spontaneous events.”

Nuanced comparisons 

Among the patients who might not be good candidates for S-ICD implantation are those who need pacing for cardiac resynchronization therapy (CRT). In commentary accompanying Burke et al.’s JACC investigation report, Anne Curtis, MD, a cardiologist and distinguished professor specializing in cardiac electrophysiology at the University of Buffalo, pointed this out by way of noting the S-ICD can be appropriately implanted as a second device for patients who have endocardial pacemakers already in place.

Curtis says she believes S-ICD is breakthrough technology even if it’s only so because of its newness as an innovation. “On the other hand, it’s not going to assume the majority of the ICD