Intermittent Complete Atrioventricular Block Secondary to Scrub Typhus in a Patient With Hypothyroidism: A Case...

Scrub typhus, a common febrile illness in South Asia, can rarely cause life-threatening myocarditis with complete heart block. We report a 43-year-old man presenting with a one-week history of fever, shortness of breath, and abdominal pain. Laboratory findings showed transaminitis, hypoalbuminemia, elevated C-reactive protein, and mild hypokalemia, suggesting an infectious etiology. Electrocardiography (ECG) and 24-hour Holter confirmed complete atrioventricular (AV) block with P-wave and QRS dissociation. Although temporary pacing was initially considered due to the severity of the block, the patient remained hemodynamically stable, prompting a systematic evaluation for reversible causes. Scrub typhus IgM (enzyme-linked immunosorbent assay) was positive, confirming the diagnosis. Other potential causes such as Lyme disease (low local incidence), ischemic heart disease (ruled out by the absence of chest pain, normal troponin levels, and unremarkable ECG findings), AV-nodal blocking agents (no relevant medication history), and autoimmune or infiltrative conditions (not clinically suspected) were systematically excluded. Although hypokalemia was identified and corrected, it failed to improve the heart block, suggesting it was not the underlying cause. Similarly, hypothyroidism was unlikely to explain the early improvement, as levothyroxine typically takes weeks to take effect. Scrub typhus-associated myocarditis was thus considered the probable cause. The patient was treated with doxycycline 100 mg twice daily and levothyroxine 25 μg daily with continuous cardiac monitoring. Within 72 hours, the fever resolved, and the ECG showed restoration of a sinus rhythm with sinus bradycardia, confirming AV block resolution. Doxycycline was continued for 14 days. This case illustrates that scrub typhus can serve as a reversible etiology for bradyarrhythmias and cardiac conduction abnormalities. While complete heart block frequently necessitates urgent pacing, it is imperative to actively pursue reversible causes. This underscores the significance of clinical vigilance in endemic regions, where early recognition and prompt initiation of antibiotic therapy can avert serious cardiac complications and reduce the necessity for invasive interventions.