Lyme Carditis

Lyme carditis is cardiac infection with Borrelia burgdorferi sensu lato, transmitted by Ixodes ticks. It is a manifestation of early disseminated Lyme disease. It develops in about 1 to 4% of untreated adults in North America and in up to 10% in some European series.

Onset is usually 3 days to 7 months after the bite (median about 3 weeks), and men are affected about three times as often as women. The dominant lesion is atrioventricular (AV) block, which fluctuates and can progress from first degree to complete block within minutes to hours.

Myopericarditis, left ventricular dysfunction and arrhythmia are less frequent. Death is rare with treatment. The disease is confined to temperate regions of the Northern Hemisphere (north eastern and upper Midwest United States, Europe, parts of Asia).

Locally acquired Lyme carditis is not established in sub-Saharan Africa. There, heart block in a young adult is more often due to rheumatic carditis, tuberculosis, HIV-associated disease, sarcoidosis, degenerative conduction disease or drugs, unless the patient has travelled to an endemic region.

Pathophysiology. Spirochaetes invade the myocardium and conduction tissue and provoke a lymphocytic and plasma cell infiltrate. The block usually lies at the AV node, so the QRS is narrow and escape rhythms are junctional.

Because the process is inflammatory and not structural, conduction usually recovers within 1 to 2 weeks of antibiotics and almost always within 6 weeks.

• Tick exposure in an endemic area, often not remembered. Erythema migrans (expanding annular rash) is present in under half of patients with carditis. Facial nerve palsy, meningitis, radiculitis and migratory arthralgia may coexist.
• Light headedness, syncope or presyncope, palpitations, dyspnoea, chest pain and fatigue. Some patients are asymptomatic.
• Bradycardia, irregular pulse from dropped beats, cannon a waves, pericardial rub, and signs of heart failure when myocarditis is present.
• ECG: first degree AV block (commonest early finding), Mobitz type I or II second degree block, complete block with a narrow complex junctional escape, bundle branch block, ST-T change and QT prolongation.

Red flags.

• Syncope or presyncope
• PR interval of 300 ms or more, or rapid PR lengthening on serial ECGs
• Second degree or third degree AV block
• Hypotension, heart failure or reduced ejection fraction
• Raised troponin
• Ventricular arrhythmia
• Concurrent meningitis or other neurological disease

• Clinical diagnosis. Endemic exposure, a conduction or myopericardial syndrome and supportive serology. Erythema migrans in an endemic area is diagnostic without serology.
• Serology. Two tier testing: a sensitive enzyme immunoassay, then IgM and IgG immunoblot. IgM is interpreted only within 30 days of symptom onset. Serology can be negative in the first 2 to 4 weeks, so repeat a convalescent sample after 2 to 4 weeks when suspicion is high.
• Continuous telemetry and 12-lead ECG with serial PR measurement.
• Troponin, natriuretic peptide, CRP, potassium, thyroid function. Echocardiography for ventricular function and effusion. Cardiac MRI when myocarditis is suspected. Endomyocardial biopsy is rarely needed.
• Lumbar puncture when headache, meningism or cranial nerve palsy is present.
• Co-infection testing (Babesia, Anaplasma) in endemic regions where the tick also carries them.

Differential diagnosis.

• Degenerative or ischaemic AV block
• Acute viral myocarditis and rheumatic carditis
• Cardiac sarcoidosis (the leading cause of unexplained AV block in adults under 60 years)
• Chagas disease (travel or residence in Latin America)
• Diphtheria and tuberculous myopericarditis
• Infective endocarditis with root abscess
• Drug induced block (beta blockers, verapamil, diltiazem, digoxin, amiodarone) and hyperkalaemia
• Congenital AV block and vagally mediated block in athletes

• Admit with telemetry for syncope, dyspnoea, chest pain, second degree or third degree block, or first degree block with PR of 300 ms or more. Patients with first degree block under 300 ms and no symptoms can be treated as outpatients with oral therapy, ECG at 1 week and repeat ECG if symptoms appear.
• Intravenous therapy until PR is under 300 ms and no higher grade block is present for 24 hours:
  • Ceftriaxone 2 g intravenously once daily (children 50 to 75 mg/kg once daily, maximum 2 g). Monitor for biliary sludging and diarrhoea. In combined severe renal and hepatic impairment, limit to 2 g daily with levels where available.
  • Alternative: cefotaxime 2 g intravenously every 8 hours (maximum 6 g daily), with dose reduction at creatinine clearance under 20 mL/min.
• Oral completion to a total of 14 days (range 14 to 21 days), started once block has settled:
  • Doxycycline 100 mg orally twice daily (children 8 years and over 4.4 mg/kg daily in 2 doses, maximum 100 mg each dose). Avoid in pregnancy. Counsel on photosensitivity and take with water and food.
  • Amoxicillin 500 mg orally three times daily (children 50 mg/kg daily in 3 doses, maximum 500 mg each dose). Give 500 mg every 12 hours at creatinine clearance 10 to 30 mL/min.
  • Cefuroxime axetil 500 mg orally twice daily.
• Conduction support.
  • Temporary transvenous pacing for symptomatic high grade block, haemodynamic compromise or pauses. Transcutaneous pacing as a bridge.
  • Atropine 500 micrograms intravenously every 3 to 5 minutes, maximum 3 mg, can speed a nodal rhythm but is unreliable in infranodal block.
  • Stop drugs that slow AV conduction.
  • Permanent pacing is not needed in most patients, because conduction recovers. Consider it only when high grade block persists beyond 2 to 6 weeks of treatment, in which case reconsider the diagnosis.
• Corticosteroids and anti-inflammatory drugs are not routine. Use them only for significant myopericarditis with ventricular dysfunction after specialist review, because evidence is limited.
• Heart failure or arrhythmia is managed with the usual drugs, with care over beta blockers and calcium channel blockers while conduction is impaired.
• A Jarisch-Herxheimer reaction (fever, rigors, hypotension in the first 24 hours) can occur. It is managed supportively, and antibiotics are continued.

Special groups.

• Pregnancy: ceftriaxone intravenously, then amoxicillin to complete the course. Avoid doxycycline.
• Region: in non-endemic regions, treat empirically only with a compatible exposure history and positive serology. Otherwise investigate other causes of heart block.

Monitoring. Continuous ECG during admission. ECG at discharge, at 1 to 2 weeks and at 4 to 6 weeks, until PR is normal. Echocardiography when troponin or natriuretic peptide was raised. Serology is not repeated to judge cure, because antibodies persist.

Referral and escalation. Refer to cardiology and infectious diseases. Urgent for syncope, high grade block, haemodynamic compromise, myocarditis with reduced ejection fraction, or no recovery of block within 2 to 6 weeks.