The advent of transvenous leads did away with thoracotomies when
putting in implantable cardioverter-defibrillator (ICD) systems,
making the procedure simpler and safer. Will the device therapy take
a similar leap forward if ICDs that use a single subcutaneous lead
become available? The availability could happen next year, according
to one of the earliest investigators of just such a device; as for
the leap, time will tell.

Currently called the subcutaneous ICD (S-ICD) by its developer,
Cameron Health (San Clemente, CA), the "active can" generator is
optimally positioned in a pocket under the arm, with the other
electrode threaded horizontally under the skin "about an inch away
from the center of the sternum," Dr Andrew Grace (Papworth Hospital
NHS Trust, Cambridge, UK) told heartwire.

The preferred pulse-generator and lead positioning and
defibrillation thresholds (DFTs) had been worked out over the past
six years or so, in some respects culminating with a small crossover
trial presented at the European Society of Cardiology Congress 2005.
As reported by heartwire at the time, 26 patients had been
randomized to be temporarily implanted with the S-ICD system first,
followed by a standard transvenous system, and 27 others received
them in the reverse order.

No fluoroscopy was allowed during S-ICD lead positioning; only
anatomic landmarks could be used, Grace had explained at the meeting
in Stockholm, Sweden.

At DFT testing, the mean effective energies for the two
configurations were 36.6 J for the S-ICD and 11.1 J for the
conventional system.

The S-ICD's greater energy requirements make for a generator that is
slightly larger than what is typical for the smallest of today's
ICDs, according to Grace. But that disadvantage may be more than
offset by the system's potential benefits. Implantation doesn't
entail doctor or patient radiation exposure, for example, and
complications related to vascular access are avoided. "We will be
able to deal with lead problems much more easily. For example, an
infection will not be systemic, it will be local," he said.

A series of about 60 patients implanted with the S-ICD is expected
to be published in early 2009, Grace said, and data from at least
that many patients will be presented to European regulators the same
year.