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A 36-year-old man presents to an emergency department (ED) in New York City. He reports feeling poorly for the past 3 weeks, with fatigue and muscle aches and pain throughout his body. He says he has no known premorbid illnesses, nor has he been in contact with anyone who is ill. He drinks alcohol occasionally, he says, but is not a smoker and does not use recreational drugs.

He tells clinicians that his symptoms began during a camping and hiking trip in upstate New York, and were initially accompanied by fever and cough that resolved within a few days.

He reports noticing that his heart rate, which he measures at home using a wearable device, is in the 40s (beats per minute), and he has been having palpitations and feeling lightheaded and dizzy. He has not had chest pain or been short of breath, and on further questioning, clinicians learn that he has not been affected by presyncope, syncope, nausea, vomiting, diarrhea, constipation, or abdominal pain, and has not had any tick bites, rash, or joint pain.

His most recent camping trip before this last one was 2 months earlier.

Assessment in the ED finds that at the time of his presentation his heart rate is fluctuating between 30 and 70 bpm, and his blood pressure is 130/78. Physical examination reveals irregular first and second heart sounds with a cannon A wave on jugular vein examination; findings for other organ systems are unremarkable.

Rapid SARS-COV-2 polymerase chain reaction and antibody tests are negative.

Blood analyses show a slightly elevated leukocyte count (12.54 × 10⁹/L), and a complete metabolic panel is normal. Troponin T is within normal range, and blood cultures are also negative.

Lyme variable major protein-like sequence total antibody, as well as Western blot immunoglobulin (Ig)G and IgM, are positive.

Electrocardiograph (EKG) assessment identifies a sinus rhythm at 61 bpm with a third-degree atrioventricular (AV) block. There is no evidence of acute pulmonary disease on chest x-ray.

Transthoracic echocardiography shows an ejection fraction of 60% with normal diastolic function and cardiac dimensions. Based on the absence of cardiac risk factors, chest pain, or suggestive EKG findings, and the patient's normal cardiac troponin, clinicians consider it unlikely that his heart block is due to cardiac ischemia.

Likewise, they rule out possible sarcoidosis, a known cause of heart block in the young, given that there are no signs of erythema nodosum, shortness of breath, or blurred vision, and chest x-ray and serum calcium level are both normal.

Given that the patient's constitutional symptoms developed shortly after the camping trip, along with the presence of positive Lyme antibodies and complete heart block, the medical team makes a diagnosis of Lyme carditis.

The patient is started on constant telemetry monitoring, and receives intravenous (IV) ceftriaxone 2 g daily for 7 days. Due to the high-risk features, the team also places a transcutaneous pacemaker for 5 days.

After a week of treatment, the patient's symptoms and cardiac conduction abnormalities improve considerably, and he is switched to oral amoxicillin 500 mg twice a day. When his PR interval is maintained below 300 ms for more than 72 hours, he is discharged home with a prescription for the same antibiotics for an additional 21 days.

When the patient returns to the clinic 20 days later for follow-up, he reports that his symptoms are completely resolved. Examination shows that he has a regular heart rate of 73 bpm and blood pressure of 124/77, and he is cautioned about the need to protect himself from tick bites when outdoors.

Discussion

Clinicians presenting this of a patient who presented with cardiac symptoms and EKG abnormalities secondary to Lyme disease note that a prompt diagnosis using the relatively new Suspicious Index in Lyme Carditis scoring system and initiation of appropriate antibiotics helped avoid unnecessary placement of a permanent pacemaker, as EKG and clinical perturbations are reversible.

The natural course of Lyme disease generally involves an early, localized stage that begins a median of 12 days (range of 5-48 days) after a tick bite causes infection with the Borrelia burgdorferi spirochete. Lyme disease manifests as erythema migrans (EM) rash associated with flu-like illness and fever, which usually resolve within 3-4 weeks, with or without antibiotic treatment.

Lyme disease, the most common vector-borne infectious disease in the U.S., has an annual incidence of about 23,500 cases, mostly in the northeastern and north-midwestern parts of the country and typically occurring in June to December.

According to , the average incidence of confirmed Lyme disease cases per 100,000 persons in 2018 occurred in Maine, with 83/100,000 and in the highest 3-year average there was 92 cases/100,000. Other states with high incidences (i.e., at least 10 confirmed cases per 100,000 persons) are Minnesota, West Virginia, and Wisconsin.

Associated cardiac abnormalities such as conduction disturbances are rare, representing only 1.1% of Lyme disease cases reported to the CDC between 2001 and 2010, the case authors note.

Cardiac manifestations are a late clinical feature of Lyme disease in untreated patients, who usually present with a varying degree of AV block, which may cause dizziness, syncope, and shortness of breath with or without chest pain. The SILC score was developed to assess the likelihood that a patient's second- or third-degree AV block is due to Lyme carditis.

This risk-stratification method assigns scores to various risk factors to categorize patients into low, intermediate, and high risk for Lyme carditis:

• One point is assigned for each of the following: age younger than 50, male sex, outdoor activity, or living in an endemic area

• Two points are given for the following constitutional symptoms of Lyme disease: fever, malaise, arthralgia, dyspnea, presyncope, or syncope

• Three points are given for having a history of a tick bite

• Four points are given for having EM rash

A total score of 1-2 represents a low probability, 3-6 is an intermediate probability, and 7-12 is a high probability.

Although Lyme disease affects both women and men equally, cardiac manifestation of Lyme disease is more common in men. Acute Lyme carditis manifests mostly as different degrees of AV block; high-degree AV block is the most common, accounting for approximately 90% of Lyme carditis.

Other manifestations include arrhythmias, pericarditis, myocarditis, and pancarditis, and these may cause cardiogenic shock, sudden death, or cardiac arrest, the case authors note.

Chronic Lyme carditis typically occurs as chronic heart failure in a patient with positive serologies and endomyocardial biopsy. The authors note that the entity of chronic Lyme carditis is a contentious issue in the literature, as is the association between Borrelia infection and the development of dilated cardiomyopathy.

Treatment

The case authors explain that because there is little published research or evidence guidelines about the treatment of Lyme carditis and no evidence to indicate that parenteral antibiotic therapy is more effective than enteral antibiotic therapy, they themselves recommend that IV antibiotics be started in patients with an intermediate or high SILC score, even before serology results, which may take many days or even weeks to return.

Specifically, the team advises the following:

• Use of , followed by oral antibiotics for a total course of 14-21 days

• , with a switch from IV to oral once the high-grade AV block resolves and the PR interval is less than 300 ms; the low-probability group should have a standard permanent pacemaker

Cardiac magnetic resonance imaging may help confirm the diagnosis of Lyme carditis, since the presence of wall edema with increased signal intensity on T1-weighted images reflects myocardial inflammation, although endomyocardial biopsy is a criterion standard for confirming myocarditis of any etiology.

This patient's normal systolic and diastolic functions on echocardiography and the absence of any clinical evidence of heart failure precluded the need for endomyocardial biopsy. Based on his SILC score of 5 with a positive Lyme serology, clinicians started the patient on IV ceftriaxone on the day of admission and placed a transcutaneous pacemaker.

Within 48 hours of IV ceftriaxone, treatment was associated with a significant clinical improvement of fatigue and palpitations, along with EKG improvement as the AV block evolved from a third- to a first-degree AV block.

After continued IV ceftriaxone for 7 days with telemetry monitoring and daily EKGs, the patient was discharged on oral amoxicillin for 3 more weeks, and an EKG on the day of discharge showed sustained electrocardiographic improvement.

Conclusion

The authors conclude that with appropriate treatment, the prognosis of Lyme carditis is good. Patients with high-degree infra-Hisian block usually recover within a week; those with first-degree conduction disorder also recover, but it can take longer, typically up to 6 weeks.

Prompt diagnosis, however, is key: In a patient whose only clinical manifestations of Lyme carditis are cardiac symptoms and EKG abnormalities, use of the SILC scoring system and initiation of appropriate antibiotics can abrogate the need for unnecessary insertion of a permanent pacemaker since electrocardiographic and clinical perturbations are readily reversible.

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