Ordinarily, a pacemaker is surgically implanted below the collarbone, where it sits in a sizable pocket under the skin. Electrical leads run from it to the heart, allowing it to monitor the rhythm of the heartbeat, and deliver electrical pulses to adjust that rhythm as needed. Now, however, Minnesota-based St. Jude Medical has announced upcoming availability of "the world’s first and only commercially available leadless pacemaker." Known as the Nanostim, it's reportedly less than 10 percent the size of a regular pacemaker, and is inserted directly into the heart via a minimally-invasive procedure.
The device was developed by the Nanostim company, which was recently acquired by St. Jude.
It's implanted into the heart using a steerable catheter that is fed into the femoral vein via a small incision in the inner thigh. This leaves a considerably smaller scar than is the case with the usual chest pocket, plus unlike a regular pacemaker, the Nanostim can't be seen or felt bulging beneath the skin.
The process is illustrated in the following video.
More importantly, however, the procedure reduces the risk of infections that can occur in the pocket, and there are no leads to break or detach – according to St. Jude, the leads "have historically been recognized as the most vulnerable component of pacing systems," and patients' activities often have to be limited in order to avoid damaging them.
Inside of the Nanostim is an electrode that delivers electrical pulses to the heart when necessary, along with a battery that's about the size of a AAA. That battery should be good for about 8.5 years of use. When it needs to replaced, the pacemaker can be retrieved in the same manner in which it was implanted.
The Nanostim recently received CE Mark approval, so it should soon be available for general use in some European markets. It has so far only achieved approval for use in clinical trials in the US.