Leadless Cardiac Pacemaker: Does Anatomical Position at Implant Affect Long-Term Electrical Performance?

A pacemaker (or artificial pacemaker) is a medical device which uses electrical impulses, delivered by electrodes contracting the heart muscles, to regulate the beating of the heart. The permanent leadless cardiac pacemaker (LCP) has been shown to be safe and effective in human clinical trials. However, there is little information on the effect of implant location on LCP performance; the aim of this study was to determine whether anatomic position affected the long-term pacing performance of the LCP. 

In the study, patients who enrolled in the Leadless II IDE Clinical Trial and had finished 6 months follow-up (n = 479, mean age: 75.7 ± 11 years old) were selected for the study. The LCP that was implanted (Nanostim^TM, St. Jude Medical) is an entirely self-contained, active-fixation, rate-adaptive pacemaker that is 42-mm long with a maximum diameter of 6.00 mm. The LCP was delivered to the right ventricle through the use of a specially designed delivery system and was anchored in the right ventricle with the use of a helical screw-in fixation electrode at the distal end of the device. The implanting investigators determined the LCP final position under fluoroscope, which was categorized into three groups: RV apex (RVA, n = 174), RV apical septum (RVAS, n = 101), and RV septum (RVS, n = 204). Data on capture threshold (at a 0.4 ms pulse width), R-wave amplitude and impedance were analyzed at implant, hospital discharge and 2 weeks, 6 weeks, 3 months and 6 months post-implant.

The results indicated that at implant, the mean capture thresholds in the RVA, RVAS and RVS were 0.77 ± 0.45, 0.81 ± 0.61 and 0.78 ± 0.59 volts, respectively. R-wave amplitudes were 8.0 ± 3.0 mV, 7.7 ± 2.9 mV and 7.6 ± 2.9 mV, respectively. Impedance values were 727 ± 311, 765 ± 333, and 677 ± 227 respectively. There were no differences among the 3 implant locations in capture threshold or R-wave amplitudes at 6 months (P > 0.06); however, all 3 performance parameters significantly improved over time (P < 0.001).

In conclusion, the LCP implant location does not affect capture thresholds or R-wave amplitudes at 6 months, and there is little effect on impedance. Although implant location does not appear to be a predictor of electrical performance, additional long-term data will help guide optimal implant location, which would minimize the risk of perforation or dislodgement. And additional studies with a longer duration of follow-up are needed to fully evaluate the pacing performance of the LCP as these devices last for many years.

Article by John Ip, et al, from USA and Canada.

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Image by Servier Medical Art, from Flickr-cc.