NEW ORLEANS — The many problems associated with traditional transvenous-lead implantable cardioverter-defibrillators could evaporate if a novel, totally subcutaneous lead system bears out the early promise displayed in its initial randomized clinical trial, Gust H. Bardy, M.D., said at the annual meeting of the Heart Rhythm Society.
Although inappropriate shocks are the most frequent adverse events associated with ICD therapy, it's the transvenous-lead complications, including lead fractures and infections, that cause electrophysiologists and surgeons to quake. Lead complications often result in surgical revision or device explantation.
And then there is the complex and time-consuming nature of the implantation procedure. “Part of the reason ICDs aren't used more is the referral bottleneck issue. Special skills are required,” observed Dr. Bardy of the Seattle Institute for Cardiac Research.
He reported on 51 adults with a standard indication for ICD therapy who participated in a randomized international trial sponsored by Cameron Health Inc., developer of the subcutaneous-only ICD lead system. All patients first received this system, which was inserted without fluoroscopy. Then they got standard transvenous leads. The study's purpose was to learn whether defibrillation is possible with a totally subcutaneous lead system at energy levels within the range of what's technically feasible.
The answer proved to be yes, although as expected the mean defibrillation threshold was 3.5-fold greater with the subcutaneous lead system: 36.1 J, compared with 10.9 J with the transvenous system.
“It's quite amazing, really, that without an electrode in the heart the defibrillation threshold can be as low as 5 J—and perhaps even lower,” said Dr. Bardy, who is a consultant to and holds an equity position in Cameron Health. The average insertion time for the subcutaneous-only lead systemwas 6 minutes.
Dwight W. Reynolds, M.D., chief of cardiology at the University of Oklahoma Health Sciences Center, Oklahoma City, called the new lead system “a revolutionary technology” that electrophysiologists will be watching closely.
Andrew E. Epstein, M.D., offered a more guarded assessment. “We have no outcome data for this system. Furthermore, there was no information presented about sensing. So we have a long way to go,” said Dr. Epstein, professor of medicine at the University of Alabama, Birmingham.