Probable Lyme carditis in pacemaker candidates with atrioventricular block: Preliminary results from northern Serbia

OBJECTIVES: This study aimed to estimate the proportion of patients with newly diagnosed cardiac conduction disorders requiring pacemaker implantation who have serological findings consistent with probable Lyme carditis in endemic northern Serbia. METHODS: Adults presenting with new conduction disorders and scheduled for permanent pacing were enrolled and provided serum at baseline and 4-week follow-up. Anti-Borrelia immunoglobulin (Ig)G was assessed using a two-tier algorithm (enzyme-linked immunosorbent assay screening, immunoblot confirmation). Probable Lyme carditis was defined as IgG seroconversion or stable/rising titers; no Lyme carditis was defined as persistent seronegativity or declining titers. RESULTS: Of 80 enrolled patients, 74 completed follow-up (92.5%; mean age 71.6 years; 68.9% male). Third-degree atrioventricular block was most frequent (56.8%). Probable Lyme carditis was identified in eight of 74 (10.8%) patients. Of 14 patients who were enzyme-linked immunosorbent assay-reactive/borderline, six (42.9%) were immunoblot-negative. Seropositive patients were older (age 76.3 vs 71.1 years); titers were higher in men at 4 weeks. IgG positivity was associated with suspected Lyme carditis (relative risk 6.8 at baseline; 16.2 at 4 weeks). No participant reported a recent tick bite or erythema migrans. CONCLUSION: Approximately one in 10 pacemaker candidates showed serological patterns compatible with probable Lyme carditis. Incorporating two-tier paired serology into evaluation of high-grade conduction disorders in endemic settings may improve etiologic diagnosis and inform management.