Excerpt:

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.