A 54-year-old American woman presented with an episode of syncope. This had occurred against a background of several days of dizziness and palpitations. Her medical history included Bell’s palsy, which had been diagnosed three weeks earlier. On examination, she had a resting bradycardia of 31 beats per minute and her electrocardiogram demonstrated third-degree atrioventricular (AV) block. She was referred to cardiology for consideration of permanent pacemaker implantation. Given her facial nerve palsy and AV block, a diagnosis of
Lyme borreliosis was suspected. Within 48 hours of initiation of ceftriaxone, she reverted to sinus rhythm, albeit with a marked first-degree AV block. Subsequent serology confirmed the diagnosis. Reversible causes of complete AV block should always be considered and appropriate therapy may avoid the need for permanent pacemaker insertion.