First case report of inducible heart block in Lyme disease and an update of Lyme carditis

Background Lyme disease (LD), is the most common vector-borne illness in the US and Europe, with predominantly cutaneous, articular, cardiac and neuro-psychiatric manifestations. LD affects all layers of the heart and every part of the conducting system. Carditis is a less common manifestation of LD. Heart block (HB) as the initial and sole manifestation of LD is rare. Inducible HB has never been reported in LD. We report a case of heart block (HB) inducible with exercise and reversible with rest. Case presentation A 37-year-old male presented to the emergency department after experiencing two episodes of syncope while at work. He presented, with a heart rate of 57 bpm, and the ECG showed sinus bradycardia with first degree AV block. The PR interval was 480 ms (NL 120–200 ms). Physical exam was unremarkable. The cardiologist’s initial impression was vaso-vagal attack. He developed high degree AV block during a stress test for the initial work up, which resolved on cessation of exercise. A similar episode while walking in the hallway, resolved at rest. The high degree AV block appeared inducible with exercise and reversible with rest. His Lyme serology was strongly positive. He was treated with ceftriaxone and doxycycline. After completing treatment, the patient had a normal ECG and returned to work without limitations, doing manual labor. Conclusions Manifestations of Lyme carditis (LC) vary from asymptomatic and symptomatic electrocardiographic changes and heart block (HB) reversible with treatment, to sudden death. HB as the sole and initial presentation of LC is rare. There have been no reports of inducible HB in LD. Here we present a case of inducible and reversible high degree HB in a case of LC and an update of literature. Exercise and stress testing should be avoided in suspected cases of LC until resolution of carditis. Lyme carditis should be suspected in individuals with cardiac manifestations in an endemic area, particularly in the younger patients with no other etiology evident.


Case presentation
A 37-year-old male with past medical history significant for asthma, anxiety, and former tobacco use, presented to our emergency department after experiencing two episodes of syncope while at work. He was employed outdoors in a heavy manual labor industry. He and his co-workers have been frequently bitten by ticks at work in the past. Initial vital signs on admission were significant for bradycardia, with a heart rate of 57 bpm, and the ECG showed sinus bradycardia with first degree AV block, with a PR interval of 480 ms (NL 120-200 ms) (Fig. 1). Physical exam was unremarkable, except for hypopigmentation of fingers. Serum ALT level was elevated 115 (NL 12-78). Other labs on admission were all within normal including serum troponin. Further workup included a normal CT scan of head, a vascular study of the carotid vessels that showed minor right sided carotid stenosis of < 50%, and an echocardiogram that was unremarkable,except for mildly increased LV wall thickness with an EF of 60%. An exercise stress test done by the cardiologist, was terminated early. The patient developed dyspnea, and his ECG demonstrated progression of first-degree AV block to high degree AV block (Fig. 2). Once back at rest, the patient's high degree AV block reverted to first degree AV block. He had a similar episode while walking in the hallway wearing a Holter monitor, on day 5, also reversible with rest. He was transferred to the critical care unit for close monitoring and treated with ceftriaxone 2G iv once daily and doxycycline 100 mg orally twice daily. The first-degree AV block improved with a gradual decrease in the PR interval (Table 2). His Lyme serology (Western Blot) was strongly positive ( Table 3).
The heart block significantly improved to 270 ms by day 7 of treatment. He was discharged and continued outpatient IV Ceftriaxone for 3 weeks. After completing treatment, the patient had a normal ECG with PR interval of 178 (Fig. 3) on day 16 and an uneventful exercise stress test. He returned towork without limitations, doing manual labor. He has been symptom free for 2 years. Now he uses tick-repellents at work.
Progression of first-degree heart block to second degree and then to complete heart block without treatment has been reported. Regression of complete heart block  to second degree, then first degree followed by complete resolution with treatment is also known [32]. Inducible heart block in Lyme disease has not been reported. We present the first report of inducible heart block in a patient whose initial and sole manifestation of LD was HB. First-degree heart block worsened to high degree AV block on exercise, which was reversible with rest and reproducible during the hospitalization.
As illustrated in this case, exercise and stress testing should not be carried out in LD patients until complete recovery from heart block. HB secondary to Lyme disease rarely requires a permanent pacemaker. However, patients with a PR interval greater than 300 ms should be monitored in an intensive care setting, as they may rapidly progress to complete HB [30]. A temporary pacer is sometimes required; however, most patients respond to treatment within two to three weeks. The antibiotics used in LC include amoxicillin [12], ceftriaxone [8,9,32,36,38,41,53], doxycycline [49] and ceftriaxone and doxycycline [13,37]. Duration of treatment varied from 2 weeks to one month.
LC may present with HB as the sole [53] or initial presentation [45,66] with or without other manifestations of LD [30,32,36,37,48] or with multiple electrocardiographic (Table 1) and clinical presentations. First degree HB is the most common manifestation, which could rapidly progress to CHB [32]. It is important to keep a high degree of suspicion for Lyme disease in endemic areas in patients with cardiac symptoms with or without other manifestations of LD, particularly younger individuals with no other etiology evident. Some patients with complete heart block may need a temporary pacemaker [26,39,47,55,66,67]. The majority of AV blocks in LC are reversible with antibiotic treatment. Exercise is contraindicated until resolution of LC.

Acknowledgements
We acknowledge the assistance of Dr. Amit Prasad, MD and Dr. Renu Toshniwal, MD for involvement in patient care.

Funding
No funding was received for the study.
Availability of data and materials All data generated or analysed during this study are included in this published article. Additional data analysed during the current study are available from the corresponding author on reasonable request.

Consent for publication
Written Informed consent was given by patient and wife for publication of this case report with Lyme test results and ECG findings.