Electrocardiographic Progression From Complete Heart Block to Normal Sinus Rhythm in Lyme Carditis Following Antibiotic Therapy: A Case Report.

Lyme disease is a leading vector‑borne illness in the United States, and its geographic range has been expanding into the Midwest, including Michigan. Although Lyme carditis is an uncommon complication, it can produce rapidly progressive atrioventricular (AV) conduction disturbances, including complete heart block, that mimic intrinsic cardiac disease and may lead to unnecessary permanent pacemaker implantation if not recognized. We describe a 19‑year‑old woman with a history of postural orthostatic tachycardia syndrome who presented with headache, nausea, vomiting, palpitations, chest discomfort, and bilateral arm paresthesias. She had recently recovered from an upper respiratory infection but denied rash or focal deficits. On presentation, she was bradycardic and borderline hypotensive, and an electrocardiogram showed complete heart block. Laboratory testing revealed elevated inflammatory markers and cardiac biomarkers. She required a temporary transvenous pacemaker and was admitted for management. Lyme serology returned positive, and intravenous ceftriaxone therapy was initiated. Over several days, her AV conduction improved from complete heart block to first‑degree block and ultimately to normal sinus rhythm. The temporary pacemaker was removed, and she completed a course of intravenous antibiotics at home via a peripherally inserted central catheter. This case illustrates the reversible nature of high‑degree AV block caused by Lyme carditis. Early recognition of the condition in young patients with unexplained conduction abnormalities in tick‑endemic areas enables appropriate antimicrobial therapy and avoids unnecessary permanent pacing.