Leadless Cardiac Pacemakers: Back to the Future
Leadless Cardiac Pacemakers: Back to the Future
For the current generation of single-unit LCPs, the most important limitation is their ability to perform only single-chamber pacing, specifically right ventricular pacing. Therefore, these devices would not be appropriate for most patients with sinus node dysfunction, who derive significant clinical benefit from dual-chamber sensing/pacing. Although multichamber systems (atrioventricular and biventricular) are in development, there are currently no available data on the feasibility of these systems. Device-device communication and fixation mechanisms (in the morphologically distinct right atrium) are just a few of the challenges that must be overcome before multicomponent systems can become a reality (Central Illustration). To our knowledge, there have not been any chronic device embolizations with single-component systems, but this remains a potential source of concern. The optimal fixation mechanism, with regard to both chronic performance and the need for future extraction, remains to be seen. The long-term reliability and accuracy of rate-responsive features, now that the sensor has been relocated from the subcutaneous pulse generator to the intraventricular space, is not yet known. However, the ongoing LEADLESS II trial is assessing rate-response characteristics (as a secondary endpoint) in a series of patients undergoing graded exercise testing. Furthermore, although the single-component systems are, by volume, significantly smaller than conventional cardiac pacemakers, the portion of the device that interacts with the endocardium has a wider diameter, which has raised the possibility of proarrhythmia. The delivery system for single-unit leadless pacemakers includes a large venous sheath (24-F for the TPS and 18-F for the LCP) and delivery catheter. The larger caliber of the delivery units has the potential to increase complications related to either the femoral access site or catheter manipulation within the right ventricle. Indeed, in the LEADLESS study, the one and only major procedural complication (cardiac perforation and subsequent death) was related to the delivery catheter. Further refinements in technique and technology are likely to mitigate the chance of this complication. Although leadless pacemakers are reportedly retrievable acutely, the ability to remove a chronically-implanted device remains untested in humans. As such, the strategy for device management (retrieval vs. abandonment) once the battery has been depleted remains to be determined. As with any emerging technology, special training will be required to develop proficiency in LCP implantation. On one hand, many of the technical and cognitive skills overlap with those used in common electrophysiologic procedures (e.g., fluoroscopic imaging, manipulation and implantation of devices within the right ventricle); on the other hand, additional skills will undoubtedly require further proctoring/training (e.g., large venous sheaths, intraprocedural positional integrity testing). Future clinical competency statements will likely address this matter.
(Enlarge Image)
Central Illustration.
Leadless Cardiac Pacemakers
ICD = implantable cardioverter-defibrillator.
Potential Limitations of Leadless Cardiac Pacing
For the current generation of single-unit LCPs, the most important limitation is their ability to perform only single-chamber pacing, specifically right ventricular pacing. Therefore, these devices would not be appropriate for most patients with sinus node dysfunction, who derive significant clinical benefit from dual-chamber sensing/pacing. Although multichamber systems (atrioventricular and biventricular) are in development, there are currently no available data on the feasibility of these systems. Device-device communication and fixation mechanisms (in the morphologically distinct right atrium) are just a few of the challenges that must be overcome before multicomponent systems can become a reality (Central Illustration). To our knowledge, there have not been any chronic device embolizations with single-component systems, but this remains a potential source of concern. The optimal fixation mechanism, with regard to both chronic performance and the need for future extraction, remains to be seen. The long-term reliability and accuracy of rate-responsive features, now that the sensor has been relocated from the subcutaneous pulse generator to the intraventricular space, is not yet known. However, the ongoing LEADLESS II trial is assessing rate-response characteristics (as a secondary endpoint) in a series of patients undergoing graded exercise testing. Furthermore, although the single-component systems are, by volume, significantly smaller than conventional cardiac pacemakers, the portion of the device that interacts with the endocardium has a wider diameter, which has raised the possibility of proarrhythmia. The delivery system for single-unit leadless pacemakers includes a large venous sheath (24-F for the TPS and 18-F for the LCP) and delivery catheter. The larger caliber of the delivery units has the potential to increase complications related to either the femoral access site or catheter manipulation within the right ventricle. Indeed, in the LEADLESS study, the one and only major procedural complication (cardiac perforation and subsequent death) was related to the delivery catheter. Further refinements in technique and technology are likely to mitigate the chance of this complication. Although leadless pacemakers are reportedly retrievable acutely, the ability to remove a chronically-implanted device remains untested in humans. As such, the strategy for device management (retrieval vs. abandonment) once the battery has been depleted remains to be determined. As with any emerging technology, special training will be required to develop proficiency in LCP implantation. On one hand, many of the technical and cognitive skills overlap with those used in common electrophysiologic procedures (e.g., fluoroscopic imaging, manipulation and implantation of devices within the right ventricle); on the other hand, additional skills will undoubtedly require further proctoring/training (e.g., large venous sheaths, intraprocedural positional integrity testing). Future clinical competency statements will likely address this matter.
(Enlarge Image)
Central Illustration.
Leadless Cardiac Pacemakers
ICD = implantable cardioverter-defibrillator.