Features February 2014 Issue

New Cardiac Device Works Without Touching the Heart

The implanted defibrillator detects and delivers shocks, but no leads are inserted into the veins. The technology does have some limitations, however.

A new type of defibrillator that is implanted under the skin can detect dangerous changes in heart rhythms and provide shocks that restore a healthy rhythm, all without a single wire attached to the heart itself.

The new S-ICD System includes a standard implantable cardioverter defibrillator. However, the lead stops at the sternum, and no wires extend into the heart.

The subcutaneous implantable cardiac defibrillator called the S-ICD System from Boston Scientific, was shown to be safe and effective in a six-month study. The research was published in the American Heart Association journal Circulation.

Bruce Wilkoff, MD, director of Cardiac Pacing and Tachyarrhythmia Devices at Cleveland Clinic, says that while the system has some limitations, this first-generation device has some clearcut advantages over traditional ICDs that have wires or leads that run through veins and touch the heart directly.

“The largest benefit is the avoidance of lead extraction for either broken leads or difficult vein access due to occlusion or infection,” Dr. Wilkoff explains. “For a patient who needs therapy for decades, this is an important goal. It may be the most important issue for patients who need hemodialysis.”

Hemodialysis is a process that uses a machine to help filter waste products, salt and fluids from the blood when the kidneys are no longer capable of that function. Patients with kidney failure often have trouble with their veins.

How it works
Like other ICDs, this new device includes a battery-powered component that is implanted under the skin in the chest cavity. The Boston Scientific model is placed near the left armpit. A lead is then threaded from the device over the ribs to the sternum, but still under the skin. The lead then extends vertically to an area just below the neck.
Normally, more than one lead would extend from the defibrillator into the heart through veins. Those leads would carry a slight electrical charge that would shock the heart if an abnormal rhythm (arrhythmia) was detected.

However, extracting broken or defective leads from the heart is a delicate and not uncommon aspect of traditional ICD therapy. Eliminating this potentially risky step is seen as a very positive development in cardiac device technology.

The S-ICD System can administer the same kind of shock as a traditional ICD, though Dr. Wilkoff notes that more energy is required in this type of ICD compared to devices with leads in the heart.

Limitations
The new S-ICD differs from standard ICDs in other important ways. Many ICDs can also act as pacemakers, which means that in addition to detecting and responding to arrhythmias, they can also speed up a slow heart rhythm and slow down a racing heart. The S-ICD system doesn’t provide that pacemaker therapy.

And unlike other ICDs, this model cannot be monitored remotely. New ICDs typically can provide information about the number of shocks it has provided and other data to a doctor’s office wirelessly.

Dr. Wilkoff also notes some other key limitations or downsides to the device. “It’s larger (than traditional ICDs), so it requires three incisions instead of one,” he explains. “Our clinical experience with it is limited, so there’s less certainty about its effectivness to prolong life. However, there is great promise, and will likely see a significant number of patients receiving this device.”

He adds that this is a first-generation device, so future versions of the S-ICD will probably be smaller and require fewer incisions. They may last longer without having to be replaced. Subsequent models may also be more programmable to include pacing capability.

About the S-ICD
The S-ICD system was approved by the U.S. Food and Drug Administration (FDA) in 2012, but the American Heart Association makes clear that more long-term study is required. This most recent six-month study was conducted at 33 centers around the U.S., and involved more than 300 patients. Results showed that 99 percent of patients with the S-ICD System implanted were free of complications for at least 180 days after implantation. The goal set by the FDA to demonstrate safety and effectiveness was 79 percent. The device also was 100 percent effective in correcting purposely-induced arrhythmias.

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