Lyme Carditis With Complete Heart Block Successfully Treated With Oral Doxycycline.

Lyme disease is a vector-borne infection that can affect multiple different organ systems. Lyme carditis represents one of these sequelae and is defined by acute onset of high-grade atrioventricular block in the presence of laboratory-confirmed infection. Current guidelines recommend patients with Lyme carditis be admitted for close cardiac monitoring and intravenous antibiotics therapy. Our case illustrates an active duty male who was initially diagnosed with Lyme disease after initially reporting symptoms including headache, fever, eye pain, and rash, with subsequent development of exercise intolerance 6 weeks later. An electrocardiogram (ECG) obtained at that time was misinterpreted as first-degree heart block, and he was initiated on oral doxycycline therapy and referred to cardiology. On follow-up to cardiology clinic, the prior ECG was reviewed and interpreted as complete heart block. A repeat ECG showed resolution of the heart block, and exercise stress testing showed chronotropic competence. This case illustrates the resolution of complete heart block in Lyme carditis with oral doxycycline, suggesting this antibiotic as a possible alternative treatment agent.