PATIENTS WITH ATRIO VENTRICULAR BLOCK
AND NORMAL SINUS NODE FUNCTION
In the DDD mode, if the lower rate of the pacer is programmed at a sufficiently low value to permit atrial tracking, the pacemaker stimulates the ventricle synchronous with intrinsic P waves. If a patient does not require atrial pacing, it may be reasonable to implant a dual-chamber pacer with a single tripolar or quadripolar lead that allows atrial sensing and ventricular pacing and sensing ( Fig. 16p ). These VDD pacing systems allow for ease of implant and for bipolar atrial sensing. Atrial sensing may not be as reliable compared to a fixed atrial lead, which may lead to occasional atrial '81 In a recent prospective comparison between single-lead VDD systems to DDD leads, however, there were lower P-wave amplitudes in the group with VDD systems, but no significant clinical differences with respect to atrial undersensing.
In the Safety and Effectiveness Trial for the Nanostim Leadless Pacemaker (LEADLESS II) trial, a leadless pacer was implanted successfully in 504 of 523 patients. At six months, 90% of patients met the primary efficacy endpoint of acceptable pacing threshold (≤2 V at ms) and sensing amplitude (≥5mV or value greater than or equal to evaluate implantation). 93% of the patients met the primary safety endpoint of freedom from device-related serious adverse events. Device related serious events were seen in % of patients, including device dislodgment with percutaneous retrieval, cardiac perforation and pacing threshold elevation requiring retrieval and device replacement. 5
The DEXTRUS pacing lead is an extendable-retractable, active fixation lead designed to provide a larger electrically-active surface area for enhanced threshold performance. The lead features a familiar feel with durable and predictable helix extension-retraction performance and an inner coil designed for predictable torque response. The DEXTRUS lead is designed for an easy lead implant experience with mapping capability, a radiopaque helix and tip extension indicator and a flexible tip designed for flexible placement options within the right atrium and right ventricle.