Exercise-Induced Heart Block in Lyme Carditis: A Rare Case Report

Lyme carditis can affect the heart’s electrical conduction system.
Heart block may worsen with physical activity before treatment.
Most conduction abnormalities improve with appropriate antibiotic therapy.

Lyme carditis is an uncommon manifestation of Lyme disease that primarily affects the heart’s electrical conduction system. Patients may develop first-degree atrioventricular (AV) block, higher-degree AV block, complete heart block, bradycardia, or less commonly other cardiac rhythm disturbances. Most cases improve with appropriate antibiotic treatment, making early recognition especially important.

Although Lyme carditis is generally reversible with timely antibiotic treatment, recent reviews note that a subset of patients may experience persistent conduction abnormalities or other long-term cardiac sequelae, highlighting the importance of prompt diagnosis, treatment, and appropriate follow-up.^1,2

Symptoms of Lyme carditis may include syncope, lightheadedness, palpitations, chest pain, shortness of breath, or fatigue. This case report describes the first published patient with Lyme carditis whose heart block worsened during exercise testing and improved again with rest. The case highlights an important clinical lesson: patients with active Lyme carditis should avoid exercise stress testing until their conduction abnormalities have completely resolved.

Exercise revealed worsening heart block

In their article “First case report of inducible heart block in Lyme disease and an update of Lyme carditis”, Kannangara and colleagues describe the first reported case of exercise-induced heart block in Lyme disease.

The 37-year-old man initially presented to the emergency department after experiencing syncope. “ECG showed sinus bradycardia with first degree AV block, with a PR interval of 480 ms (NL 120–200 ms),” the authors wrote.

A markedly prolonged PR interval greater than 300 ms has been associated with an increased risk of progression to high-grade AV block and generally warrants continuous cardiac monitoring until the conduction abnormality improves.^2,3

An exercise stress test performed by his cardiologist was terminated early when the patient developed dyspnea. During exercise, his ECG demonstrated progression from first-degree AV block to high-degree AV block.

The majority of AV block in Lyme carditis is reversible

Once the patient returned to rest, the 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,” the authors explained.

The patient was diagnosed with Lyme disease based on his history of tick exposure, positive IgG Western blot, exclusion of alternative causes, and his clinical recovery following treatment with intravenous ceftriaxone followed by oral doxycycline.

He returned to work and remained symptom-free during 2 years of follow-up.

This case also reinforces an important feature of Lyme carditis. Although high-degree AV block can appear alarming, conduction abnormalities often improve rapidly once appropriate antibiotic therapy is started. Recent reviews suggest that while most patients recover completely, a small subset may have persistent conduction abnormalities or other cardiac sequelae, underscoring the importance of continued follow-up after treatment.²

Cardiac manifestations of Lyme disease

Kannangara and colleagues also summarized the wide range of cardiac rhythm abnormalities reported in the medical literature. Although atrioventricular (AV) block is the most common cardiac manifestation, other conduction disturbances and arrhythmias have been described.

• First-degree AV block
• Wenckebach phenomenon (Mobitz type I)
• Mobitz type II AV block
• Complete heart block (high-degree AV block)
• Bundle branch block
• Sinus arrest and sinus pauses
• Supraventricular tachycardia
• Atrial fibrillation
• Junctional tachycardia
• Fascicular tachycardia
• Ventricular tachycardia
• Ventricular flutter
• Bradycardia
• Narrow QRS escape rhythm
• Prolonged QT interval
• ST-segment depression and T-wave inversion
• ST-segment elevation
• Asystole
• Sudden death in a patient with Lyme carditis and pre-existing Wolff-Parkinson-White syndrome

Clinical pearls from the authors

• Lyme carditis may present with heart block as the sole or initial manifestation of Lyme disease.
• First-degree AV block is the most common cardiac manifestation but may rapidly progress to complete heart block.
• Exercise or stress testing should be avoided until heart block has completely resolved.
• Lyme carditis should be considered in younger patients from endemic regions who develop otherwise unexplained conduction abnormalities or cardiac symptoms.

Frequently Asked Questions

Can Lyme disease affect the heart?

Yes. Lyme disease can affect the heart through Lyme carditis, an inflammatory condition involving the heart’s electrical conduction system. Heart block is the most common manifestation, although other rhythm disturbances have also been reported.

Can Lyme disease cause an irregular heartbeat?

Yes. Lyme carditis has been associated with bradycardia, AV block, atrial fibrillation, supraventricular tachycardia, ventricular arrhythmias, and other conduction abnormalities. AV block remains the most common cardiac complication.

Can Lyme disease cause tachycardia?

Yes. Although Lyme carditis most commonly causes bradycardia and AV block, supraventricular and ventricular tachyarrhythmias have also been reported. Persistent tachycardia has many possible causes and should be evaluated in the appropriate clinical setting.

Is Lyme carditis reversible?

In most patients, conduction abnormalities improve with appropriate antibiotic treatment. Temporary pacing may occasionally be necessary, but permanent pacemaker implantation can often be avoided because the heart block is usually reversible.

Clinical Takeaway

This unique case demonstrates that exercise may temporarily worsen conduction abnormalities in patients with active Lyme carditis. Clinicians should recognize that heart block can rapidly progress during physical activity, even when resting ECG findings appear relatively stable.

Most patients with Lyme carditis recover completely with prompt antibiotic treatment, but careful cardiac monitoring and appropriate follow-up remain important because a small number of patients may experience persistent cardiac abnormalities.

Related Articles

Lyme Carditis Diagnosis: ECG Findings and Clinical Clues
Lyme Carditis ECG Findings and Symptoms
Can We Avoid Using a Pacemaker for Lyme Carditis with High-Degree AV Block?
First Case of Reversible Complete Heart Block Due to Lyme Disease Reported in Canada

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Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention