Lyme Carditis and Complete Heart Block

Complete heart block is the best-known complication of Lyme carditis.
Most patients recover with prompt antibiotic treatment.
Early diagnosis may help avoid an unnecessary permanent pacemaker.

Lyme carditis is an uncommon but potentially life-threatening complication of Lyme disease. It most often affects the heart’s electrical conduction system, where inflammation can slow or completely block the transmission of electrical impulses between the upper and lower chambers of the heart. Prompt recognition and antibiotic treatment often allow normal heart conduction to recover, helping many patients avoid permanent pacemaker implantation.

After nearly four decades of treating Lyme disease, I have learned that complete heart block can occasionally be the first sign of disseminated infection. Patients may initially complain only of fatigue, lightheadedness, palpitations, chest discomfort, or fainting before an electrocardiogram reveals a serious conduction abnormality.

Complete heart block caused by Lyme carditis is a medical emergency requiring prompt evaluation, cardiac monitoring, and antibiotic treatment. Fortunately, unlike many other causes of complete heart block, Lyme carditis is often reversible when recognized early.

A systematic review by Yeung and Baranchuk summarized the diagnosis and management of Lyme carditis with high-degree atrioventricular (AV) block and introduced the Suspicious Index in Lyme Carditis (SILC) score to help identify patients most likely to have Lyme carditis.¹

How Lyme Carditis Causes Complete Heart Block

After Borrelia burgdorferi spreads beyond the original tick bite, the bacteria may invade cardiac tissue. Inflammation involving the AV node and surrounding conduction system can interfere with the normal transmission of electrical impulses from the atria to the ventricles.

The most common cardiac manifestation is atrioventricular block, which may progress rapidly from first-degree AV block to second-degree block or complete heart block. Because conduction abnormalities may fluctuate over hours, patients require close observation until the rhythm stabilizes.

Patients with Lyme carditis may experience:

• lightheadedness
• dizziness
• palpitations
• shortness of breath
• chest discomfort
• fainting (syncope)

For more information about the cardiac manifestations of Lyme disease, see Lyme carditis.

Most Lyme Carditis Heart Block Improves with Antibiotics

One of the distinguishing features of Lyme carditis is that the conduction abnormality frequently improves after appropriate antibiotic treatment. Yeung and colleagues reported that high-degree AV block often resolves within approximately 10 days, although recovery times vary among patients.¹

The authors caution that premature implantation of a permanent pacemaker may expose patients to unnecessary lifelong device-related complications if the underlying infection is promptly recognized and treated.

Although most patients recover normal AV conduction, complete recovery is not universal. A recent review found that persistent conduction abnormalities, myocarditis, ventricular dysfunction, and other long-term cardiac sequelae have been reported in a minority of patients, highlighting the importance of appropriate follow-up after recovery.²

What Is the SILC Score?

Because many patients initially present with unexplained high-degree AV block, Yeung and colleagues developed the Suspicious Index in Lyme Carditis (SILC) score to estimate the likelihood that Lyme disease is the underlying cause.

The SILC score assigns points for clinical features commonly associated with Lyme carditis:

• Age younger than 50 years (1 point)
• Male sex (1 point)
• Outdoor activity or residence in an endemic area (1 point)
• Constitutional symptoms such as fever, malaise, joint pain, or shortness of breath (2 points)
• History of a tick bite (3 points)
• Erythema migrans rash (4 points)

The total score categorizes patients as:

• Low suspicion: 0–2 points
• Intermediate suspicion: 3–6 points
• High suspicion: 7–12 points

In preliminary validation, the SILC score correctly identified 93.2% of published Lyme carditis cases and reached 100% sensitivity when complete clinical information was available.¹

The SILC score should be viewed as a clinical aid rather than a substitute for physician judgment. It is most useful when considered alongside the patient’s history, physical examination, electrocardiographic findings, and laboratory evaluation.

Lyme Carditis Involves More Than Heart Block

Although atrioventricular block is the hallmark of Lyme carditis, cardiac involvement is not limited to the conduction system. Reported manifestations include myocarditis, pericarditis, atrial and ventricular arrhythmias, and, less commonly, ventricular dysfunction or heart failure.^2,3

Most patients improve with appropriate antibiotic therapy. However, recent reviews emphasize that persistent myocardial inflammation and other long-term cardiac sequelae have been reported in a small subset of patients. These observations reinforce the importance of careful diagnosis, appropriate treatment, and follow-up, particularly after severe Lyme carditis.²

When Should Patients Be Tested for Lyme Disease?

Yeung and colleagues recommend Lyme disease serologic testing for patients with an intermediate or high probability of Lyme carditis, corresponding to a SILC score of 3 or greater.¹

Because Lyme carditis is an early disseminated manifestation of Lyme disease, prompt recognition is essential. Delaying treatment while waiting for laboratory confirmation may allow conduction abnormalities to worsen.

For more information about the strengths and limitations of testing, see Why Lyme Tests Miss Lyme Disease.

Can Lyme Carditis Blood Tests Be Negative?

Blood tests are an important part of the evaluation, but they should never be interpreted in isolation.

Yeung and colleagues note that antibody tests may occasionally be negative before the immune response has fully developed. As they explain, “negative serology does not always rule out early Lyme infection.”¹

However, Lyme carditis generally develops during the early disseminated stage of Lyme disease. By this point, most patients have detectable IgM antibodies, IgG antibodies, or both.

A positive antibody test must also be interpreted carefully because antibodies may remain detectable long after an earlier infection has resolved. A positive test alone does not prove that Lyme disease is causing the patient’s current cardiac illness.

The diagnosis should instead consider the complete clinical picture, including:

• possible tick exposure
• erythema migrans or other Lyme manifestations
• constitutional symptoms
• electrocardiographic findings
• timing of symptom onset
• alternative causes of heart block

Should Antibiotics Begin Before Test Results Return?

For patients with an intermediate or high suspicion of Lyme carditis, Yeung and colleagues recommend beginning antibiotic therapy while Lyme serologic testing is still pending.¹

Current treatment guidelines generally recommend hospitalization and intravenous ceftriaxone for patients with symptomatic Lyme carditis, second- or third-degree AV block, complete heart block, or marked PR prolongation. Once AV conduction improves and the patient is clinically stable, treatment can usually be transitioned to oral antibiotics. The specific regimen should be individualized according to the severity of illness and the patient’s clinical response.

The treatment protocol described by Yeung and colleagues reflected the evidence available in 2018. Current management should also incorporate more recent guideline recommendations and individual patient factors. For additional information, see Lyme disease treatment.

When Is Temporary Pacing Necessary?

Patients with high-degree AV block require close cardiac monitoring because Lyme carditis can progress rapidly from first-degree AV block to complete heart block and, in rare cases, asystole.

Yeung and colleagues write, “Asymptomatic bradycardia should be followed with cardiac monitoring, because patients with LC can progress from a prolonged PR interval to complete block and asystole, and the degree of AV block can fluctuate rapidly.”¹

Patients with symptomatic bradycardia may require a temporary pacemaker while antibiotics reduce inflammation and normal conduction returns. Approximately one-third of patients with Lyme carditis require temporary pacing during the acute illness.¹

Importantly, the need for a temporary pacemaker does not automatically mean a permanent pacemaker will be required. Many patients recover normal AV conduction once the infection has been treated.

How Is Recovery Assessed?

Before hospital discharge, AV conduction should be shown to be stable. Yeung and colleagues recommend exercise stress testing, when appropriate, to confirm that normal AV conduction is maintained during increased heart rates.¹

They also recommend repeating an electrocardiogram approximately four to six weeks after discharge to ensure that the PR interval has normalized and that no new conduction abnormalities have developed.¹

Most patients recover normal cardiac conduction following appropriate antibiotic treatment. Nevertheless, the recent review by Badheeb and colleagues highlights that a minority of patients may develop persistent conduction abnormalities, myocarditis, ventricular dysfunction, or other long-term cardiac sequelae. Although these complications appear to be uncommon, they underscore the importance of appropriate follow-up after severe Lyme carditis.²

Because complete heart block can rapidly become life-threatening, anyone with suspected Lyme carditis and significant conduction abnormalities should be evaluated and monitored in a hospital rather than managed solely as an outpatient.

For additional discussion of inflammatory heart involvement associated with Lyme disease, see Lyme disease myocarditis.

Frequently Asked Questions

Can Lyme disease cause complete heart block?

Yes. Lyme carditis can inflame the heart’s electrical conduction system and cause second-degree or complete atrioventricular (AV) block. The degree of heart block may fluctuate rapidly and, without prompt recognition and treatment, can become life-threatening.

Does everyone with Lyme carditis need a permanent pacemaker?

No. Many patients recover normal cardiac conduction after appropriate antibiotic treatment. Some patients require a temporary pacemaker during the acute illness, but a permanent pacemaker may not be necessary if AV conduction returns and remains stable.

What is the SILC score?

The Suspicious Index in Lyme Carditis (SILC) score is a clinical tool that estimates the likelihood that Lyme carditis is responsible for high-degree AV block. It combines age, sex, tick exposure, constitutional symptoms, erythema migrans, and other clinical findings to help guide evaluation.

Can Lyme carditis blood tests be negative?

Occasionally. Antibody tests may be negative early in the immune response. However, because Lyme carditis usually develops during early disseminated Lyme disease, most patients have detectable antibodies by the time cardiac symptoms appear. Blood test results should always be interpreted alongside the patient’s clinical presentation.

Can Lyme carditis cause long-term heart problems?

Most patients recover completely after prompt antibiotic treatment. However, recent reviews report that a minority of patients may develop persistent conduction abnormalities, myocarditis, ventricular dysfunction, or other long-term cardiac complications. Additional research is needed to better identify which patients remain at risk.

Clinical Takeaway

Lyme carditis should always be considered in younger patients or anyone with possible tick exposure who develops otherwise unexplained high-degree or complete AV block. Early recognition, hospitalization when appropriate, cardiac monitoring, and prompt antibiotic treatment can be lifesaving.

The SILC score is a useful clinical tool for estimating the likelihood of Lyme carditis, but it should always be interpreted alongside the patient’s history, physical examination, electrocardiographic findings, and laboratory results.

Although most patients recover normal cardiac conduction after treatment, recent evidence suggests that a small subset may experience persistent cardiac complications, reinforcing the importance of appropriate follow-up.

Prompt diagnosis and treatment of Lyme carditis may restore normal heart conduction, reduce the need for permanent pacemaker implantation, and improve long-term cardiac outcomes.

Related Articles

5 Things to Know About Lyme Carditis
Lyme Disease Myocarditis
Lyme Disease Treatment

References

1. Yeung C, Baranchuk A. Systematic Approach to the Diagnosis and Treatment of Lyme Carditis and High-Degree Atrioventricular Block. Healthcare (Basel). 2018;6(4):119.
2. Badheeb M, Ahmed A, Stolear A, et al. Long-term Cardiac Sequelae in Lyme Carditis: A Review. Curr Cardiol Rev. 2026;22(4):e1573403X395575.
3. Floyd WE 4th, Krulewitz NA, Lentz SA. Lyme Carditis: More Than Atrioventricular Block. Ann Emerg Med. 2026;88(2):178-180.

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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