SAN FRANCISCO – An entirely subcutaneous implantable cardioverter defibrillator accurately detected and successfully converted all episodes of ventricular fibrillation in a multicenter Dutch study that constitutes the largest experience to date using the novel technology.

"For us, so far, it has been a viable alternative to conventional ICD systems in selected patients," Lara Dabiri Abkenari said in presenting the study results at the annual meeting of the Heart Rhythm Society.

Session cochair Dr. Luc Jordaens, who was Ms. Abkenari’s senior coinvestigator in the study, went further: He said that "viable alternative" is too conservative an assessment now that a software upgrade has improved the detection algorithm and greatly reduced inappropriate shocks.

"We are now at the stage where we often see the subcutaneous ICD as the first choice," declared Dr. Jordaens, professor of cardiology at Erasmus University, Rotterdam, the Netherlands.

The subcutaneous ICD has generated considerable interest among cardiologists and patients because – unlike conventional transvenous ICDs – it is easily implanted without fluoroscopy, it requires no vascular access, and the lead is simple to remove if necessary. A smaller experience with the subcutaneous system that was reported last year attracted a great deal of attention (N. Engl. J. Med. 2010;363:36-44). The system, by Cameron Health Inc., is approved for the European market and is under review at the Food and Drug Administration.

The system comprises a pulse generator, a subcutaneous lead that has two sensing electrodes, and about 8 cm of shock coil. It has no pacing or resynchronization capabilities.

"This is for patients who need defibrillation. It’s restricted to patients who would not benefit from antitachycardia pacing. ... In a nutshell, it’s a shock box," explained Ms. Abkenari, an electrophysiology fellow and Ph.D. candidate at Erasmus.

She reported on 98 patients (mean age, 56 years) who received the subcutaneous ICD and have been followed for a median of 9 months, during which the system identified 14 nonsustained ventricular arrhythmia episodes in 5 patients and treated 28 sustained episodes in 4 patients. The mean time to treatment with an 80-J shock was 13.9 seconds.

The system also delivered 22 inappropriate shocks to eight patients because of oversensing. Since the software upgrade, however, there have been no further inappropriate shocks.

In addition to inappropriate shocks, other major complications included infections requiring explantation in five patients, hematomas not requiring device removal in three patients, and lead migration or dislodgement in three patients.

The pulse generator box is placed in a left lateral thoracic subcutaneous pocket. The lead is tunneled from the pocket to the xiphoid process, where the tip of the electrode is sutured to a sleeve attached to the xiphoid fascia. The xiphoid sleeve is an innovation that has eliminated the lead migration problems that were seen early in the study.

The generator box is substantially larger than those used in conventional transvenous ICDs. On a thin patient, the box is very obvious under the skin. The lateral position results in arm contact with movement, albeit with no pain.

Because the subcutaneous ICD preserves the vasculature, Ms. Abkenari sees the device as particularly attractive for relatively young, active patients who may need surgery later, such as individuals with hypertrophic cardiomyopathy who may one day need myomectomy or a heart transplant. The subcutaneous device has been placed in several children in the Dutch study with favorable results.

Discussant Dr. Bruce L. Wilkoff expressed reservations about the current iteration of the subcutaneous ICD.

"What naturally happens as you roll out a new technology is you start to understand it better and you see some of the warts," observed Dr. Wilkoff, director of cardiac pacing and tachyarrhythmia devices at the Cleveland Clinic and professor of medicine at Case Western Reserve University, Cleveland.

He called the 5% infection rate that resulted in device removal in the Dutch study "most disturbing."

"The hope was that infection would be more easily managed with this system," noted Dr. Wilkoff.

He also zeroed in on the four patients who required shocks for 28 sustained ventricular arrhythmic episodes.

"It’s hard to imagine that those patients wouldn’t have benefited a little bit from ATP [antitachycardia pacing]. It seems to me that ATP may be an important component of what’s needed in a device," Dr. Wilkoff continued.

That being said, he cautioned that important new medical technologies rarely spring up full grown. Refinements made along the way can make all the difference between success and failure.

"It’s not really fair to take the initial experiences or the updated experiences or the next experiences to make your total evaluation of a therapy. We all have to be careful to reserve some judgment here in seeing where the value is," he commented.

Ms. Abkenari and Dr. Wilkoff declared having no relevant financial interests. Dr. Jordaens is a consultant to Cameron Health, which makes the subcutaneous ICD.

Subcutaneous ICD Deemed "Viable Alternative"