Lyme Carditis Diagnosis: Study of 18 Cases Reveals Broader ECG Patterns

A study of 18 Lyme carditis cases shows that the condition can present with a wider range of ECG abnormalities than previously recognized. The findings suggest clinicians should expand their diagnostic thinking beyond classic atrioventricular (AV) block when evaluating cardiac patients in Lyme-endemic areas.

Lyme carditis occurs when the Lyme disease bacteria affect the heart’s electrical system. Symptoms and warning signs are discussed in more detail in Lyme carditis: when heart symptoms can’t wait.

Common Symptoms of Lyme Carditis

Lyme carditis symptoms can vary depending on how the infection affects the heart’s electrical system. While atrioventricular (AV) block is the most recognized manifestation, patients may initially present with more subtle symptoms.

Common Lyme carditis symptoms include:

• chest tightness or chest pain
• dizziness or lightheadedness
• shortness of breath
• palpitations
• fatigue
• fainting or near-fainting episodes

These symptoms may develop within weeks of infection and can occur even before Lyme disease is recognized. Because Lyme carditis can cause rapidly changing heart rhythm abnormalities, early recognition and treatment are critical.

Understanding the Mechanism of Lyme Carditis

“Lyme carditis is caused by direct invasion of myocardial tissue by spirochetes and an immunological host response causing lymphocyte inflammation,” writes Marcos in a discussion of Lyme carditis diagnosis. Furthermore, “Borrelia burgdorferi has a predisposition to cause inflammation of the atrioventricular (AV) node resulting in variable conduction abnormalities.”

This mechanism explains why Lyme carditis often presents with heart block. The spirochetes preferentially infiltrate the AV node, disrupting the electrical pathway between the upper and lower chambers of the heart. However, this case series demonstrates that the cardiac manifestations may extend well beyond classic conduction abnormalities.

Patient Demographics

The 18 patients with possible Lyme carditis were predominantly Caucasian males with a mean age of 44.5 years (range 24–79). This pattern aligns with broader epidemiologic data showing young to middle-aged males are most commonly affected by cardiac Lyme disease.

All patients met the CDC surveillance case definition for Lyme disease, although the diagnostic pathway varied:

• One patient had an erythema migrans rash with negative blood tests, demonstrating that serology can be negative even with clinical Lyme disease.
• 17 patients had 2–3 IgM-specific bands for Lyme disease.
• 5 patients presented with erythema migrans rash.
• 11 patients had 5 or more IgG bands, suggesting longer-standing infection.

The presence of one patient with negative serology but clinical diagnosis reinforces a critical point: Lyme carditis diagnosis cannot rely solely on laboratory testing when clinical suspicion is high.

Clinical Presentation

“The most common symptoms at presentation were chest tightness, dizziness, and dyspnea on exertion and symptoms had been present for 4–30 days,” writes Marcos.

This timeline is diagnostically significant. Lyme carditis typically occurs early in the disease course, often within weeks to two months after infection.

Despite early symptom onset, many patients experience diagnostic delays because clinicians may not initially consider Lyme disease when evaluating cardiac complaints.

ECG Findings: Broader Than Expected

The 18 patients exhibited a wide range of abnormal ECG findings beyond classic AV block:

• 4 patients – AV block (first- and second-degree)
• 6 patients – right bundle branch conduction abnormalities
• 2 patients – new onset atrial fibrillation
• 3 patients – T-wave inversion
• 1 patient – sinus bradycardia with ST elevation
• 2 patients – prolonged QT interval

Only 4 of the 18 patients (22%) presented with classic AV block. The remaining 78% had other ECG abnormalities that might not immediately trigger consideration of Lyme carditis.

This distribution challenges the assumption that Lyme carditis equals AV block. Clinicians evaluating unexplained cardiac conduction abnormalities, arrhythmias, or repolarization changes in endemic areas should include Lyme disease in the differential diagnosis.

Literature Review Confirms Broader Spectrum

Marcos and colleagues found a growing number of Lyme carditis cases in the medical literature. While atrioventricular conduction abnormalities remain the most common presentation, documented cases also included:

• right bundle branch block (RBBB)
• left bundle branch block (LBBB)
• widening of the QRS complex
• AV dissociation
• atrial fibrillation
• ventricular dysfunction
• fulminant myocarditis
• cardiac arrest

The authors conclude that the spectrum of ECG abnormalities in Lyme disease may be broader than previously suspected.

Diagnostic Implications

These findings have important clinical implications. Traditional teaching emphasizes AV block as the hallmark of Lyme carditis. But this case series shows that relying solely on heart block to trigger Lyme disease consideration may miss many cases.

In my practice, I maintain a broad differential diagnosis for unexplained cardiac presentations in patients from endemic areas, including:

• new arrhythmias without structural heart disease
• bundle branch blocks in younger patients
• ECG changes that do not fit classic coronary syndromes
• unexplained bradycardia
• systemic symptoms such as fever, fatigue, or malaise occurring with cardiac abnormalities

Lyme carditis remains an important but sometimes overlooked complication of Lyme disease, particularly in younger patients from endemic regions.

Frequently Asked Questions

What ECG findings suggest Lyme carditis?

While AV block is most recognized, Lyme carditis can present with bundle branch blocks, atrial fibrillation, T-wave inversions, bradycardia with ST elevation, or prolonged QT interval.

Can Lyme carditis occur with negative Lyme tests?

Yes. Serologic tests may be negative early in infection. Clinical findings such as erythema migrans or compatible cardiac symptoms may support the diagnosis.

How quickly do Lyme carditis symptoms develop?

Lyme carditis typically occurs within 1–8 weeks after infection during early disseminated Lyme disease.

Is Lyme carditis only AV block?

No. This study found only 22% of patients had AV block, demonstrating a broader range of cardiac manifestations.

Who should be tested for Lyme carditis?

Patients in endemic areas with unexplained arrhythmias, conduction abnormalities, or cardiac symptoms should be evaluated for Lyme disease.