LAUSR

Since permanent pacemakers were introduced nearly 60 years ago, the technology paradigm has consisted of a subcutaneous generator connected to separately placed epicardial or transvenous leads. Despite substantial improvements in lead and generator technology, leadand pocket-related complications continue to be troublesome, occurring in up to 15%–20% of patients. The permanent leadless pacemaker implanted by transvenous catheter technique therefore represents an important and paradigm-changing technology. The Medtronic Micra transcatheter pacing system (TPS) was recently approved in the United States on the basis of a pivotal trial of 725 patients, 99.2% of whom had successful device implantation, with a major complication rate of 3.3%. An additional model, the St. Jude Medical Nanostim leadless cardiac pacemaker, has been approved in Europe. Leadless pacing has a number of potentially attractive features. Certain risks, such as pneumothorax, lead fracture, and pocket erosion, are eliminated. Others, such as system infection, may be reduced, although this remains to be proven. Perhaps most significantly, all else being equal, many patients are likely to prefer a pacemaker that leaves no external signs of its presence in the body. While the paradigm of the leadless pacemaker is attractive, there are a number of limitations and unanswered questions raised by existing technology. Leadless pacemakers have been approved for use only in the right ventricle, and only 15%–20% of pacemakers implanted in the United Sates are single chamber. In addition, the long-term safety, efficacy, and proven longevity of leadless pacemakers are currently unknown, as is cost-effectiveness relative to established transvenous systems. A key unanswered question is how the problem of device replacement at the end of service will be handled. It has not yet been demonstrated that routine transvenous removal of chronically implanted devices will be possible, and several case reports have shown substantial encapsulation within 12–18 months. The safety and feasibility of routinely implanting 1 device in the right ventricle has also not been demonstrated. Maximizing the