A 52-year-old male, active hiker presented to the emergency department with fever, chills and palpitations for one week. He had noticed a 20 cm rash in his groin for 6 weeks. On examination, his vital signs were within normal limits and there was a faint, left groin rash which was about 10 cm in size. An EKG revealed sinus rhythm with PR interval of 440 msec (1st degree AV block). He was admitted and started on ceftriaxone 2 gm daily because of concern for acute Lyme disease. Overnight he was bradycardic with a heart rate in the 30s, and repeat EKG showed type I second degree AV block. A few hours later, telemetry showed third degree AV block, which was confirmed on EKG. The patient was asymptomatic except for palpitations. Initial lab work was negative for Lyme antibody including Lyme DNA PCR. He was continued on Ceftriaxone and did not require any pacemaker. He reverted back to first degree AV block and was discharged on 3 weeks of ceftriaxone and 1 week of doxycycline. Repeat lab work after 3 weeks showed positive IgM antibody against Borrelia burgdorferi.
Discussion:
Lyme carditis is an uncommon manifestation of Lyme disease, occurring in <1% of patients. Lyme carditis results from direct invasion of heart tissues and can involve all layers of the heart. Atrioventricular conduction block is the most common cardiac manifestation in Lyme disease and can progress variably and rapidly from first degree to complete heart block within minutes. Third degree AV block is the most severe form, and it can lead to a fatal arrhythmia if left untreated. Prolonged PR interval >300 msec is a strong predictor for the patient progressing into 3rd degree AV block. Therefore, patient with Lyme carditis whose PR interval is > 300 msec should be admitted for continuous EKG monitoring even if asymptomatic. Our patient initially presented with first degree AV block with PR interval of 440 msec, and rapidly progressed to third degree AV block in the matter of hours. Lyme serology can be negative in the early phase, but will be positive in later phases. Therefore, a high index of suspicion is required to diagnose and treat Lyme carditis even in the absence of positive serology.
Conclusions:
The most common cardiac manifestation of lyme carditis is atrioventricular (AV) block which can progress rapidly within minutes to hours. Recognizing the patient group that is most likely to develop third degree AV block associated with Lyme carditis is essential in providing prompt and appropriate therapy.