Lyme carditis

Article written and reviewed by Dr Luca Moretti

Lyme carditis is a manifestation of early disseminated borreliosis in which spirochetes and the inflammatory response mainly involve the conduction system. The typical presentation is atrioventricular block that changes degree rapidly, sometimes progressing from modest PR prolongation to complete block within minutes or hours. Myocarditis, pericarditis, ventricular dysfunction and tachyarrhythmias are possible, but much less characteristic.

Lyme disease is caused by the Borrelia burgdorferi sensu lato complex and transmitted by Ixodes ticks, with different species and distributions across North America, Europe and Asia. Carditis accounts for a small proportion of recognized cases and generally appears weeks or a few months after infection; apparent prevalence depends on surveillance and diagnostic criteria, whereas individual risk arises from the intersection between plausible exposure and a conduction phenotype.

Many patients do not remember a bite because nymphs are small, and erythema migrans may be absent, unnoticed or already resolved; excluding the diagnosis because these two elements are lacking means disregarding the biology of transmission. Conversely, positive serology in an endemic area does not prove that every block is borrelial, especially when age, medications, ischemia or degeneration provide a better explanation.

Recognition immediately changes management; a potentially reversible block is treated with antibiotics and temporarily protected if unstable, avoiding an unnecessary permanent pacemaker whenever possible. However, the aim of avoiding implantation must not reduce safety: syncope, advanced block and a PR interval of at least 300 ms identify a risk of progression and require hospitalization with continuous monitoring.

The clinical decision is made before every element is definitive because block may progress while serology is pending; plausible exposure, age, systemic symptoms and ECG dynamics guide initiation of antibiotics without turning a suspicion score into confirmation. After the result, the diagnosis is reassessed against the pre-test probability to prevent remote antibodies from retrospectively justifying any conduction disorder.

European Borrelia species and different vectors create a clinical geography that makes it inappropriate to apply North American prevalence estimates without adaptation. The diagnostic principle nevertheless remains stable: credible exposure, a compatible manifestation and validated testing at the appropriate disease stage; the history must therefore specify place and period with enough precision to permit a genuine epidemiological estimate.

Etiology, Pathogenesis and Pathophysiology

The tick acquires Borrelia during a blood meal and transmits it after prolonged attachment, with risk influenced by species, stage and duration. The spirochete multiplies locally and may produce erythema migrans, then disseminates through blood and tissues to the nervous system, joints and heart; carditis generally belongs to this disseminated phase and does not require cutaneous disease to still be visible.

In the heart, spirochetes and lymphoplasmacytic infiltrates are distributed through the myocardium and perivascular regions, with particular clinical expression near the atrioventricular node. Edema and inflammation transiently interrupt conduction, explaining rapid variations and recovery after treatment; permanent fibrotic destruction is much less common than in sarcoidosis and necrotizing myocarditis.

The immune response contributes to injury through cytokines, antibodies and cellular recruitment, but does not justify replacing antibiotics with immunosuppression. The primary target remains disseminated infection; corticosteroids have no established standard benefit for the block and may complicate interpretation if given without a diagnosis.

The block is frequently located at the nodal level, with a narrow-QRS escape rhythm and a relatively adequate rate, but infranodal sites may be involved. Stability depends on rate, response to exertion and perfusion, not solely on the named degree of block; a slow escape rhythm, wide QRS, hypotension or syncope requires more aggressive protection.

Myopericarditis presents with edema and cardiomyocyte injury, with troponin elevation and nonischemic LGE; it is less frequent and should not be assumed in the presence of every minimal biomarker elevation. Severe systolic dysfunction and shock are rare and require exclusion of other myocarditides, coinfections and ischemic causes; biopsy is reserved for these atypical or refractory phenotypes.

European epidemiology includes multiple genospecies and neurological or cutaneous manifestations that differ from those in North America; risk should be estimated from the actual area of exposure and the season, not from administrative residence. Hiking, forestry work, gardening and contact with tick habitats provide a more informative history than international travel alone.

The Suspicious Index in Lyme Carditis, SILC, combines age, sex, outdoor exposure or endemic area, systemic symptoms, tick bite and erythema to support suspicion in advanced block. It is a clinical tool proposed from a systematic review, not a validated diagnostic test capable of replacing serology and clinical judgment; its main value is to prompt attention to historical elements that are often omitted.

Reversibility depends on edema and inflammation predominating over destruction of conduction tissue. This explains the frequent recovery with antibiotics and distinguishes the problem from sarcoid fibrosis, but does not guarantee stability during the acute phase. The node may alternate between normal conduction and complete block until inflammation subsides, making continuous monitoring essential in severe phenotypes.

Tissue dissemination of the spirochete occurs before full antibody maturation, creating a window in which typical erythema migrans has greater clinical diagnostic value than negative serology. When carditis appears, antibodies are more often detectable, but time from onset remains essential; convalescent repeat testing is reserved for a sufficiently high probability.

Clinical Manifestations

Palpitations, dyspnea, chest pain, presyncope and syncope are the most relevant cardiac symptoms; bradycardia may be well tolerated at rest and worsen when a more advanced block develops. Syncope in a young person during tick season requires an immediate ECG, but the differential diagnosis must include sarcoidosis, giant-cell myocarditis, medications and genetic disease.

AV block may alternate among first degree, Wenckebach, 2:1 conduction and complete block during the same hospitalization. Marked PR prolongation signals an unstable system and may precede progression; telemetry and serial ECGs are necessary because a single recording does not represent behavior over the following hours.

Fever, malaise, headache, myalgias and arthralgias support disseminated disease; erythema migrans, multiple lesions, facial palsy, meningoradiculitis and arthritis provide additional clues and may require changes in antibiotic selection. Absence of a rash at the time of evaluation is common and does not exclude a previous episode.

Chest pain with elevated troponin and ST-T abnormalities represents a myopericarditic phenotype; an effusion is possible and function may decline, but coronary artery disease must be excluded according to risk. Evidence of Lyme disease does not justify attributing every pain to the heart because pleuritic, musculoskeletal and other conditions may coexist.

Supraventricular or ventricular tachycardias are rare compared with block and, if dominant, lower the threshold for seeking an alternative diagnosis. Ventricular tachycardia with multifocal LGE may indicate sarcoidosis or another myocarditis; any positive serology is therefore weighed against the phenotype rather than used as a universal explanation.

In children, fatigue, dyspnea, pain and syncope may accompany conduction disorders; treatment follows analogous principles with pediatric doses. During pregnancy, the antibiotic and route are selected according to safety and severity, avoiding tetracyclines when contraindicated; specialist management simultaneously considers infection and maternal-fetal stability.

Conduction recovery often occurs sequentially, progressing from complete block to lower degrees and then to normal conduction; normalization at rest does not immediately demonstrate an adequate response to exertion. Before discharge, some pathways use exercise testing to verify stability at increasing heart rates.

The geographic history must be precise: a hike in an endemic forested area is more informative than simply naming the region, while season and duration of exposure modify probability. The bite may go unnoticed and the patient may remember only a lesion interpreted as an insect bite; photographs of the rash, if available, help without replacing clinical assessment.

Escape rate and QRS width contribute to localizing the block and predicting its tolerance, but an apparently nodal location does not prevent progression. Atropine may have a variable response and does not replace ready access to pacing; blood pressure, consciousness, pain and congestion define urgency more than an isolated heart-rate value.

Investigations and Diagnosis

The initial ECG measures PR interval, QRS duration, rate and probable level of block, while telemetry records fluctuations and pauses. Troponin, natriuretic peptides, complete blood count, renal and liver function and electrolytes characterize injury and treatment safety; modest systemic inflammation does not exclude nodal involvement.

Echocardiography assesses function, effusion and structural alternatives; in the typical presentation of block with normal function it does not confirm the cause, but provides a reference and identifies patients with a broader phenotype. CMR is reserved mainly for troponin elevation, dysfunction, persistent pain or arrhythmias and demonstrates inflammation without being specific for Borrelia.

Microbiological diagnosis uses standard two-tier serology according to validated algorithms, with an initial immunoassay and a supplemental test or two immunoassays in modified two-tier testing. In early disseminated disease sensitivity is greater than during the first few weeks, but a very early negative result may require a convalescent sample if suspicion remains. Interpretation must respect the method and must not count isolated bands outside the algorithm.

IgM loses specificity when symptoms extend beyond the initial window and may generate false diagnoses; IgG can persist for years after a treated infection and is not a test of activity or cure. The therapeutic response of the block is clinically useful, but does not retrospectively turn equivocal serology into confirmation.

Blood PCR has limited sensitivity in disseminated disease, and endomyocardial biopsy is not routinely performed for typical carditis. Tissue assessment and CMR gain value when shock, severe dysfunction or failure to recover make another diagnosis plausible; coexistence with cardiac sarcoidosis cannot be excluded by tick exposure alone.

The differential diagnosis of block includes AV nodal drugs, inferior ischemia, myocarditides, sarcoidosis, giant-cell myocarditis, degenerative disease and electrolyte abnormalities; young age and exposure increase suspicion of Lyme disease but do not replace urgent assessment of lethal causes. A Lyme test obtained at low pre-test probability has a higher risk of being falsely positive and may lead to inappropriate avoidance of a necessary device.

Patients with significant cardiac symptoms, a PR interval of 300 ms or longer, second- or third-degree block or other arrhythmias are hospitalized with telemetry. This threshold does not mean that a PR of 299 ms is safe in every circumstance: symptoms, dynamics and level of block complete the decision; progression may be rapid and pacing equipment must be available.

When the initial test is negative but onset is very recent and probability remains high, a convalescent sample may demonstrate seroconversion. Conversely, isolated IgM beyond the appropriate window has a high risk of false positivity and requires caution; the laboratory should report the algorithm used because traditional immunoblotting and modified two-tier testing are not interpreted in the same way.

The SILC score may support vigilance in a young patient with advanced block, but it derives from published cases and has not been validated as a rule for exclusion or confirmation. A low score does not outweigh documented exposure and a high score does not make serology unnecessary; its best use is as a structured checklist of historical elements.

Treatment and Prognosis

The IDSA/AAN/ACR guidelines recommend antibiotics for a total of 14-21 days. In mild carditis, defined by first-degree block with a PR interval below 300 ms and absence of other severe features, appropriate oral regimens such as doxycycline, amoxicillin, cefuroxime axetil or azithromycin may be used according to the patient; selection and dose take age, pregnancy, allergies and coinfections into account.

In severe carditis and in hospitalized patients, intravenous ceftriaxone is used initially, with transition to oral therapy after clinical improvement and resolution of advanced block to complete the total course. Transition does not require every minor ECG abnormality to have disappeared, but does require stably safe conduction; automatically extending treatment beyond the recommended duration does not accelerate tissue recovery.

Symptomatic bradycardia that does not respond to pharmacological support requires temporary pacing. Because conduction generally recovers with antibiotics, a temporary strategy is preferred to immediate permanent pacemaker implantation; temporary active-fixation systems may allow mobility in prolonged cases. Instability and pauses, however, must not be tolerated merely to demonstrate reversibility.

Telemetry continues until the risk of progression is low and conduction is stable. Some centers perform an exercise test before discharge to verify conduction at increasing heart rates, adapting it to age and the myocarditic presentation; an abnormal response requires observation and reassessment, not necessarily immediate implantation of a permanent device.

Heart failure or myopericarditis receives cardiac treatment according to severity; anti-inflammatory agents and colchicine apply to a selected pericardial component and do not treat Borrelia. Corticosteroids are not routinely recommended for the block and do not replace antibiotics.

Prognosis is excellent in most patients who are recognized and treated, with recovery of conduction over days or weeks. Fatal cases have been described, generally in missed diagnoses or severe involvement, and justify initial caution; persistent dysfunction or conduction that does not recover should prompt reopening of the diagnosis.

Follow-up includes ECG and, according to the presentation, Holter monitoring, echocardiography and exercise assessment; serology is not repeated to demonstrate cure because antibodies persist. A temporary pacemaker is removed only after documented stability, and a permanent device is reserved for irreversible block or another independent indication.

The choice of temporary pacing considers not only rate and symptoms but also foreseeable instability, access and expected duration. A temporary active-fixation lead connected to an external generator may be preferable when recovery will require several days because it reduces immobility and dislodgement compared with less stable solutions. Every temporary system nevertheless carries risks of infection, thrombosis and perforation.

Switching from ceftriaxone to oral therapy reduces catheter complications and facilitates discharge when severe block has resolved and the patient is stable. It does not represent less effective treatment, but rather application of a recommended sequential strategy; total duration includes the intravenous days and is not restarted when the drug is changed.

Complications

Complete block may cause syncope, hypoperfusion, asystole and cardiac arrest if progression is not recognized. Its variability makes discharge based on a single improved ECG dangerous; hospitalization and monitoring turn a potentially fatal complication into a generally manageable condition.

A permanent pacemaker implanted during reversible block exposes the patient for decades to infection, malfunction, extraction and replacements. Avoiding it is an important goal, but one that remains subordinate to safety; a weak Lyme diagnosis must not be used to delay implantation when conduction remains unstable beyond the expected course.

Myocarditis with dysfunction and ventricular arrhythmias is rare and requires intensive care; in these cases recovery may be slower than that of nodal block and imaging follows edema and function. Failure to respond to antibiotics increases the probability of a concomitant or alternative diagnosis.

The Jarisch-Herxheimer reaction, caused by the inflammatory response after antibiotic treatment, may produce fever, chills and transient worsening but does not justify automatic discontinuation of therapy. In a patient with unstable conduction, any deterioration requires hemodynamic reassessment; true allergy and inflammatory reaction must be distinguished.

Neuroborreliosis or arthritis may coexist and influence antibiotic selection and follow-up; carditis is not managed by isolating the heart from the rest of the disease. Neurologists and infectious disease specialists integrate cerebrospinal fluid findings and neurological manifestations without performing unnecessary procedures.

False diagnosis resulting from nonspecific IgM may expose the patient to antibiotics, catheters and delayed identification of the true cause of the block. Conversely, ignoring plausible exposure can lead to avoidable implantation; the quality of the history and correct use of the serological algorithm protect against both forms of error.

After recovery, recurrence of block is unusual if the infection has been adequately treated, but a new exposure may cause reinfection because the disease does not confer reliable immunity. Tick-prevention measures remain necessary; new symptoms require a new assessment and are not automatically attributed to the previous episode.

Prevention is based on clothing, appropriate repellents, skin checks after outdoor activities and correct tick removal, while antibiotic prophylaxis after a bite is reserved for conditions defined by guidelines and is not prescribed for every exposure. Knowing the species, area and duration of attachment improves decision-making, but not everyone can identify the vector; development of erythema or symptoms in the following weeks requires reassessment.

After resolved carditis, antibodies may remain positive and should not be used to explain fatigue, palpitations or pain without a new cardiac assessment. Persistent symptoms may arise from deconditioning, benign ectopy, residual inflammation or another cause and are investigated according to phenotype; repeated antibiotic courses in the absence of evidence of active infection do not correct a scar or prevent future reinfection.

The patient receives written information on the meaning of the different degrees of block and on symptoms requiring urgent care because rapid dynamics may recur during early recovery. Follow-up is coordinated between infectious disease and cardiology specialists, avoiding the assumption that completion of antibiotics automatically marks the end of surveillance; stable conduction during exertion and absence of other manifestations then allow a gradual return to normal activity.

Recording the case with date of exposure, serological algorithm, maximum degree of block, need for pacing and time to recovery helps avoid vague retrospective diagnoses. These data also help identify conduction that takes longer than expected to recover or recurs, circumstances in which the physician should look for sarcoidosis, giant-cell myocarditis or degenerative disease rather than automatically prolonging antibiotics.