Study of 18 Lyme carditis cases reveals broader spectrum of ECG abnormalities than previously recognized. Findings show that clinicians should expand their diagnostic thinking beyond classic AV block when evaluating cardiac patients in endemic areas.

Understanding the Mechanism

“[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, “B. burgdorferi has a predisposition to cause inflammation of the atrioventricular (AV) node resulting in variable conduction abnormalities.”

This mechanism explains why Lyme carditis typically presents with heart block – the spirochetes preferentially infiltrate the AV node, disrupting the electrical pathway between the upper and lower chambers of the heart. But as this case series demonstrates, the cardiac manifestations extend 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 demographic 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, though the diagnostic pathway varied:

• One patient had an erythema migrans (EM) 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 of these presented with EM 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 4-30 day timeline is diagnostically significant. Lyme carditis typically occurs early in disease course – within weeks to two months after tick bite. The relatively short symptom duration before presentation suggests these patients sought care promptly when cardiac symptoms developed.

Yet despite early presentation, many patients face diagnostic delays because clinicians don’t consider Lyme disease in the differential diagnosis for cardiac complaints.

ECG Findings: Broader Than Expected

The 18 patients exhibited a wide range of abnormal EKG findings beyond the classic AV block presentation:

• 4 patients – AV block (2nd and 1st degree AV block)
• 6 patients – Right bundle branch conduction abnormalities
• 2 patients – New onset of atrial fibrillation
• 3 patients – T wave inversion
• 1 patient – Sinus bradycardia with ST elevation
• 2 patients – Prolonged QT interval

Notice that only 4 of 18 patients (22%) presented with the “classic” AV block pattern. The remaining 14 patients (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 remained 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: “The spectrum of ECG abnormalities in [Lyme disease] may be broader than that previously suspected. Clinicians should be aware of these ECG abnormalities that may be a sign of [Lyme carditis] in hyperendemic areas.”

Diagnostic Implications

These findings have immediate clinical relevance. 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 will miss the majority of cases.

In my practice, I’ve learned to maintain broad differential diagnosis for any unexplained cardiac presentation in patients from endemic areas:

• New arrhythmias without structural heart disease
• Bundle branch blocks in younger patients
• ECG changes that don’t fit classic coronary syndromes
• Bradycardia without adequate explanation
• Combination of systemic symptoms (fever, fatigue, malaise) with any cardiac abnormality

The geographic context matters enormously. In hyperendemic areas – where Lyme disease prevalence is high – the threshold for Lyme testing should be lower for any unexplained cardiac presentation.

Why Outcomes Weren’t Reported

The authors note they “were not able to address the outcome as the study was retrospective.” This limitation is common in chart review studies where long-term follow-up data may not be consistently documented.

However, other studies have established that Lyme carditis outcomes are generally excellent when treatment begins promptly. Heart block resolves, pacemakers can be removed, and patients recover completely in most cases. The critical variable is timing – early recognition and treatment versus diagnostic delay.

Clinical Perspective

This study changes how we should approach cardiac presentations in endemic areas. The diagnostic paradigm “unexplained AV block = consider Lyme” needs to expand to “unexplained cardiac abnormality = consider Lyme.”

The one patient with negative serology but clinical diagnosis deserves particular attention. This demonstrates that even with appropriate testing, laboratory results cannot override clinical judgment when the presentation suggests Lyme carditis.

I’ve seen this pattern repeatedly: young patients with new cardiac symptoms in endemic areas, testing delayed or negative, diagnosis missed until symptoms progress. The lesson from this case series is clear – broaden your suspicion, lower your threshold for testing, and don’t wait for perfect serologic confirmation to begin treatment when Lyme carditis is clinically likely.

Frequently Asked Questions

What ECG findings suggest Lyme carditis?

While AV block is most common, Lyme carditis can present with bundle branch blocks, atrial fibrillation, T wave inversions, bradycardia with ST elevation, or prolonged QT interval. Any unexplained ECG abnormality in endemic areas warrants Lyme disease consideration.

Can you have Lyme carditis with normal Lyme tests?

Yes. One patient in this series had clinical Lyme disease with EM rash but negative serology. Tests can be negative early in infection when cardiac symptoms develop, requiring clinical diagnosis.

How quickly do Lyme carditis symptoms develop?

This study found symptoms present for 4-30 days before medical evaluation. Lyme carditis typically occurs 1 week to 2 months after tick bite, often before other Lyme symptoms develop.

Is Lyme carditis only AV block?

No. While AV block is most common, this study found only 22% of patients had AV block. The majority had other ECG abnormalities including bundle branch blocks, arrhythmias, and repolarization changes.

Who should be tested for Lyme carditis?

Patients in endemic areas with unexplained cardiac abnormalities, especially younger patients without structural heart disease, those with recent tick exposure, or anyone with cardiac symptoms plus systemic symptoms like fever or malaise.