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.