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known drug allergies. He denied tobacco, alcohol, or illicit
drug use. Notably, he worked as a taxidermist at a farm.
Upon initial examination, he noted having several tick bites
a few weeks ago while working at his job, after which he
developed erythema migrans on his right arm and abdomen.
He denied any recent travel history.
Physical examination revealed a heart rate of 40 beats per
minute, blood pressure of 134/74 mmHg, respiratory rate of
20 breaths per minute, and temperature of 98.6 degree
Fahrenheit. The review of systems was remarkable for an erythematous macular rash with central clearing on the anterior
aspect of right arm. Laboratory tests, including troponin I (reference <0.04 ng/mL), were unremarkable. An initial electrocardiogram (ECG) revealed a second-degree AV block,
fluctuating between Mobitz type I and Mobitz type II heart
block, with a P-R interval of 300 ms. The patient was transferred to cardiovascular intensive care unit (CVICU) for closer
monitoring. Enzyme-linked immunosorbent assay (ELISA)
and Western immunoblot tests were performed and sent to the
laboratory for analysis. A presumptive diagnosis of Lyme carditis was established based on the confirmed history of tick
exposure, presence of erythema migrans, and AV block. The
patient was started on ceftriaxone 2 g every 24 hours. In addition, heparin 5000 units/mL subcutaneous injection every 12
hours was initiated for venous thromboembolism prevention.
All of the patient's home medications, except carvedilol and
lisinopril, were restarted. Carvedilol, a nonselective β-blocker
and α1 blocker, was held to prevent the patient's heart rate
from dropping further and worsening his bradycardia. Cardiac
Electrophysiology Service was consulted and agreed with the
primary team's plan for conservative management and did not
see a need for a pacemaker placement.
On day 3 of hospitalization, patient's heart rate was found
to be between 50 and 60 beats per minute. The diagnosis of
Lyme disease was confirmed based on the presence of
Borrelia antibodies demonstrated by ELISA and Western
immunoblot findings (positive for IgG and IgM anti-Borrelia
antibodies). A transthoracic echocardiogram revealed an
ejection fraction of 60% to 65%, normal right ventricular
systolic function, and no significant valve disease. A repeat
ECG revealed a first-degree AV block with a P-R interval of
300 ms. When compared with the initial ECG, the patient
was no longer in second-degree AV block. As the patient's
second-degree heart block had resolved, he was transferred
from the CVICU to the general medicine floor, where he
continued to receive ceftriaxone 2 g every 24 hours.
On day 5 of hospitalization, there was a marked improvement in the patient's clinical status; though, he continued to
experience weakness and fatigue. After the placement of a
peripherally inserted central catheter line, the patient was
discharged to his home on a 28-day course of ceftriaxone 2 g
every 24 hours. On the day of discharge, the patient's vitals
were as follows: heart rate of 65 beats per minute, blood
pressure of 138/74 mmHg, respiratory rate of 20 breaths per
minute, and temperature of 98 degree Fahrenheit. The patient

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did not develop any neurologic symptoms of Lyme disease
over the course of his hospital stay. Upon discharge, all of
patient's home medications, including carvedilol and lisinopril, were restarted. In addition, the patient was instructed to
follow-up with his primary care physician and cardiologist
on an outpatient basis.

Discussion
Lyme carditis is an uncommon manifestation of Lyme disease, occurring in approximately 4% to 8% of patients with
untreated Lyme disease.3 Lyme carditis results from direct
invasion of cardiac tissues by spirochetes, and can involve
all layers of the heart.4,5 Patients with Lyme carditis most
commonly present with some degree of AV conduction
blockade, which can fluctuate rapidly and progress from
a first-degree block to a His-Purkinje block within a few
minutes.6 A review of 105-patient case reports of patients
with Lyme carditis revealed that 49% of patients experienced
third-degree AV block, 16% of patients experienced seconddegree AV block, and 12% of patients experienced firstdegree AV block.7 The highest risk of progression to complete
AV block was noted to be in patients with a P-R interval of
≥300 ms.7 Even though the most common manifestation of
Lyme carditis is AV block, patients can also present with
endocarditis, myocarditis, pancarditis, pericarditis, and QTc
interval prolongation.4 Notably, 3 cases of sudden cardiac
death due to Lyme carditis have been reported to date.8 While
patients with Lyme carditis can be completely asymptomatic,
patients with a high-degree AV block usually present with
symptoms such as chest pain, palpitations, shortness of
breath, light-headedness, and/or syncope or near-syncope.3
The degree of severity of some of these symptoms typically
increases as the degree of heart block progresses.

Diagnosis
There are no standardized diagnostic criteria for Lyme carditis. Diagnosis of Lyme carditis is established primarily by
clinical and epidemiological findings. Serologic testing,
through detection of antibodies to Borrelia burgdorferi, is
used to support the clinical diagnosis.6 When performing
serologic testing, a 2-tiered approach is recommended in
which a positive or equivocal ELISA is followed by a confirmatory Western immunoblot test.8 However, as the majority
of patients with established late stage Lyme disease infection
are seropositive, seropositivity alone is not sufficient to confirm a diagnosis of Lyme carditis.6 It is imperative that serological testing be interpreted in the light of clinical
presentation and possible exposure to establish a diagnosis.6

Management
Patients who are experiencing (1) syncope, dyspnea, or chest
pain; (2) a second- or third-degree AV block; or (3) a

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