To date, there are no direct comparisons between the two currently available leadless pacing devices, though their implant complication rates and 6-month performance seem comparable, apart from acute device dislodgement, which is so far only reported in Nanostim recipients (at a rate of 1.1% in Leadless II ).
Comparison of Leadless Pacemakers to Traditional Pacemaker Systems
The reported complication rates of leadless pacemaker implantation trials of 4%–6.5% compare favourably to available transvenous data.
In the Micra TPS trial , the historical control group of 2667 de novo (of note: single- and DUAL-chamber) pacemaker recipients experienced a total major complication rate of 7.6% compared to 4.0% in the leadless group after 12 months (hazard ratio 0.52, 95% CI 0.35–0.77; P = 0.001). The reduction in major complication rate was associated with a 47% reduction in prolonged hospitalisation and 82% reduction rate in system revisions.
Nationwide analyses of cardiac pacemaker implantation complications are available for Denmark by Kirkfeldt et al. . They report a complication rate of 7.5% in single lead system implants and a 12.5% rate with dual lead transvenous pacing systems. The Follow Pace Study reported a similar rate of complications (12.5%) after single and dual chamber de novo implants .
The rate of cardiac perforation/pericardial effusion is greater in leadless pacemaker implantation than in transvenous systems. A meta-analysis of 28 studies comprising 60,744 patients found a mean incidence of lead perforation of 0.82% , whereas the rate of cardiac perforation/pericardial effusion in the two leadless PM studies was 1.6% for each.
Patients especially suitable for leadless pacing: obviously, leadless pacing is the only pacing possibility (apart from epimyocardial access with its intrinsic difficulties to provide low and stable thresholds) when the upper central venous system is damaged. This can occur after previous transvenous pacemaker or indwelling catheter infections, chest surgery, radiation for thoracic tumors, and trauma, among other reasons.
Leadless pacing should be strongly considered in patients on haemodialysis for two reasons: Firstly, for sparing the upper venous system, meaning also the access for dialysis, and, secondly, their increased rate of transient bacteriemia while being dialysed leading to haematogenous lead infection. So far, pacemaker infections have not been reported in leadless systems, presumably due to high blood flow velocities, small device size, and encapsulation in the heart.
A point of discussion is whether young adults with neurocardiogenic syncopes of the cardioinhibitory type should be offered a leadless pacing system (Fig. 1 and videos 1, 2, 3, 4 are available in enhanced content-med engine link). Of course, pacing indications in these patients should have been chosen very prudently, but on the other hand we all know the occasional young woman with frequent syncopes and documented asystoles in the range of 30 s leads to social isolation over time. We think it is justified to offer the leadless system as an alternative to conventional indwelling pacing leads given the risks of carrying them over decades to come. Even when abandoned later, they remain a time bomb ready to infect, break, or migrate at any time. Anybody who ever laser-extracted completely ingrown calcified pacemaker leads, placed in the venous system for decades, knows about the downsides. Last but not least, there is a cosmetic advantage especially taken seriously by young ladies (this sometimes results in the forgetting of being a pacemaker patient in carriers of leadless systems, since nothing reminds the patient of it).
Patients for whom leadless pacing is considered face enhanced risks. The trials identified the following risk factors for implant complications (i.e. perforation risk): elderly, frail women, low body mass index, patients on chronic steroids (this applies also for transvenous system implantations). In our own experience, the implantation can be technically challenging when dealing with enlarged right atrial and/or right ventricular diameters, generally in pulmonary hypertension patients. The preformed and fixed bending radius of the delivery sheath makes it more difficult to reach the RV and to deploy the system at the desired point and, therefore, it is prudent to avoid these patients when beginning with the technique.