Discussion
Our study supports the hypothesis that leadless devices are less prone
to haematogenous pacemaker infections. In our population, the rate of
bacteraemia was almost 10% suggesting that this was a high-risk group.
One of the most relevant finding of the study is that patients who were
previously implanted with a leadless pacemaker, do not seem to require
systematic pacemaker removal in case of bacteraemia.
Haematogenous seeding of CIED during bacteraemia is a severe condition
that is associated to significant morbidity and mortality if
unsuccessfully managed1,16. In case of pacemaker
infection, the complete removal of the hardware is a clear indication in
the guidelines2,7. Staphylococcus aureusbacteraemia has been associated with a high risk of cardiac device
related infection5. This is a result of the high
propensity of the pathogen to adhere to foreign materiel implanted in
the body including pacemaker leads17.
As leadless pacing technology is relatively new in clinical use, there
are only few reports on the risk of device
infection18,19. In our study, none of the patients had
definite sign of Micra infection in the setting of or after bacteraemia
even involving gram positive Staphylococcus . In 2 cases, the
absence of device infection was confirmed by negative culture of the
device following its preventive removal during valve surgery for
endocarditis while there was no sign of device infection on preoperative
transoesophageal echocardiographic images for both patients and on
additional 18FDG PET/CT imaging for one of the
patients. Overall, the absence of device infection in our series is also
ascertained by the absence of recurrent bacteraemia reported during the
follow up after antibiotic treatment and surgery when appropriate. Our
results are in accordance with those reported by El Chami et al. for
patients with systemic infection from the Micra IDE
study18. Among 720 patients implanted with a Micra,
the authors reported the occurrence of 21 serious infectious events
(bacteraemia or endocarditis) in 16 patients that were successfully
treated with antibiotics without evidence of leadless pacemaker
infection during follow up.
For the first time, this study reported on the use of18F-FDG/PET imaging to rule out leadless pacemaker
infection during bacteraemia. In this small series of 6 patients, there
was no increased metabolic activity detected around the device. Previous
studies have shown the utility of 18F-FDG PET/CT for
diagnosing CIED infection8-10. The sensitivity in
detecting infection was higher for infection of the generator pocket as
compared to pacing leads10. 18F-FDG
PET/CT also enabled to differentiate device infection from residual
inflammation in the early phase post-implantation8.
Adding PET/CT results to Duke criteria increased the diagnostic
sensitivity in detecting infection by the reduction of cases classified
as possible infective endocarditis9.
The absence of Micra related infection detected during bacteraemia is
reassuring. First, it might be explained by the intrinsic
characteristics of the device: the use of a parylene coating seems to
have protective effect against bacterial grow and adhesion while its
reduced size with a small surface area in contact with the bloodstream
might also be protective against bacterial
seeding11,20. Secondly, the reported progressive
fibrous encapsulation of the device could also contribute to reduce the
risk of infection. Autopsies have revealed partial device encapsulation
as early as 2 months after implantation and complete encapsulation at 1
year13,14. Finally, the absence of a pacemaker pocket
and the use of a catheter delivery system avoid all manual manipulation
of the device during the implant procedure and are also potential
factors contributing to the reduction of the risk of bacterial seeding
as compared to conventional pacemaker.
Previous studies have identified host-related risk factors for CIED that
include diabetes mellitus, end stage renal disease, chronic obstructive
pulmonary disease, corticosteroid use, history of previous infection,
renal insufficiency, malignancy, heart failure, pre-procedural fever,
anticoagulant use and skin disorders1,3,21. In our
case series, patients who developed bacteraemia after Micra implantation
had a higher incidence of end-stage renal disease treated by dialysis
and of previous valve intervention. The use of leadless pacemaker might
be of interest in these patients, reducing the risk of device-related
infection/endocarditis.