Abstract Body (Do not enter title and authors here): Description of case: A 68 y.o. woman presented to the ER with NYHA class IV heart failure symptoms and productive cough, already evaluated by pulmonologist and initiated on cefuroxime. She was hemodynamically stable, but dyspneic, with muffled heart sounds. ECG showed complete atrioventricular block (AVB), similar to a retrospectively analyzed ECG performed 4 years prior, improperly assessed at that time. Transthoracic echocardiography revealed pericardial effusion (up to 4 cm), with partial right-heart chambers collapse, without cardiac tamponade criteria. We initiated her on anti-inflammatory drugs and colchicine, and performed needle pericardiocentesis. After excluding neoplasm, tuberculosis and autoimmune diseases, laboratory findings hinted towards chronic Lyme disease (Borrelia burgdorferi serology: IgM negative, IgG positive, Western blot confirmation) and Lyme carditis. We presumed both the AVB and the effusion had developed and remained asymptomatic for at least 4 years. Thus, we considered the AVB irreversible, noting the timeline and even the recent cefuroxime administration, and proceeded with permanent pacemaker implantation. The clinical and echocardiographic course were favorable at the three-week follow-up.
Discussion: In this 68 y.o woman case, the concomitant presence of AVB and large pericardial effusion warranted extensive diagnostic work-up. Ultimately, serological assays confirmed by Western blot analysis established a diagnosis of Lyme carditis, with several remarkable features. First, the prolonged course of Lyme carditis with complete AVB and sizable pericardial effusion was facilitated by absence of symptoms over the years (notably rare in cases of complete AVB), spanning from the initial ECG showing AVB to her current presentation. Permanent pacemaker implantation emerged as the sole viable option at this particularly advanced stage of disease. Furthermore, this case describes a rare example of Lyme carditis manifesting at a markedly delayed stage of Lyme disease, a condition that typically presents during its early phase. Moreover, the presence of a large pericardial effusion deviates from the more common finding of small to moderate effusions in this clinical context. This case underscores the importance of heightened clinical vigilance and awareness regarding atypical presentations of Lyme carditis, reaffirming that sustained attention to Lyme disease and its potential systemic complications remains both crucial and timely.