Abstract Funding Acknowledgements Type of funding sources: None. Introduction Cardiac implantable electronic device (CIED) infection can present with either pocket or systemic manifestations, both necessitating complete device removal and pathogen-directed antimicrobial therapy. However, some may present with both pocket and systemic infection. We aim to characterize those with complicated pocket infection. Methods A retrospective analysis of all CIED extraction procedures at our medical center from 07/2010 to 12/2018 was performed. Patients were divided to simple pocket infection, complicated pocket infection and systemic infection groups. Results A total of 300 patients were included; 104 (34.7%) had a simple pocket infection, 142 (47.3%) had a systemic infection alone and 54 (18%) presented with a complicated pocket infection. Most were males, with a similar mean age at time of extraction. No differences in comorbidities were observed, except for higher prevalence of diabetes (54.2%) in the systemic infection group (p=0.002). Patients with a systemic and complicated pocket infection presented more frequently with leukocytosis and fever > 37.8, as opposed to the simple pocket infection group. Staph Aureus was the most common pathogen in the systemic and complicated pocket infection groups (43.7% and 31.5% respectively) while CONS predominated (31.7%) for the simple pocket infection group (10.6%, p<0.001). No differences were observed in procedural success rates or complications of the extraction procedure. Kaplan Meier survival analysis showed that at 3 years of follow-up the rate of all-cause mortality was significantly higher among patients with systemic infection compared to both pocket infection groups which were similar (p<0.001), with the curves diverging at 30 days. Multivariate analysis demonstrated high creatinine and lower albumin were predictors of 30 days and 1 year mortality while age and the presence of atrial fibrillation were predictors of 1 year mortality only. Conclusions We characterize a new entity of a complicated pocket infection. Albeit the similarity to the systemic infection group regarding clinical manifestation, those with complicated pocket infection carry a better prognosis than those with systemic infection alone. Infectious pathogen Overall survival

potential inversion was recorded in 9 (39%) patients (inversion group).Pacing threshold are significantly lower in inversion group compared to non-inversion group (implant: 1.06 6 0.8 V vs 1.86 6 0.8 V; P < 0.05, 1 week: 1.22 6 1.3 V vs 2.84 6 2.3 V; P ¼ 0.08, 1 month: 0.97 6 0.9 V vs 2.73 6 2.1 V; P < 0.05).Conclusions: HB potential inversion could be recorded during permanent HBP in 39% of patients and is associated with significantly lower pacing thresholds compared to patients in whom inversion was not recorded.HB potential inversion may be a predictor for superior short-term HB pacing thresholds.