Complete Heart Block Due to Lyme Carditis
Case Report. A 63-year-old woman with a history of hypertension, for which she was taking oral verapamil 360 mg daily, presented with a one-week history of increasing dyspnea on exertion, paroxysmal nocturnal dyspnea, ankle swelling and an 8-lb. weight gain. She admitted to having a tick bite while vacationing in Cape Cod, Massachusetts, three weeks prior, but denied any fever or rash at that time. Routine blood work and Lyme titers were drawn, and the patient was referred to a cardiologist. A week later at her cardiology appointment, she was found to be in complete heart block and referred Winthrop-University Hospital for admission.
Physical exam revealed an elderly woman in mild respiratory distress. Her blood pressure was 108/72 mmHg, with a heart rate of 50 beats per minute, respiratory rate of 16 respirations per minute, and temperature of 98.1 oF. She had small erythematous lesions on the left side of her upper back, consistent with erythema chronicum migrans. She did not have any jugular venous distention or carotid bruits. Her lung bases were dull to percussion, with decreased breath sounds. Her heart sounds S1 and S2 were audible, and no S3 gallop was noted. Abdominal exam was benign. She had 1+ pitting edema on both lower extremities.
Her chest radiograph revealed cardiomegaly, pulmonary venous congestion and bilateral pleural effusions. The electrocardiogram revealed third-degree heart block with a ventricular rate of 46 beats per minute, in the setting of an old right bundle branch block (Figure 1) present in previous electocardiogram. Her laboratory data revealed no cardiac enzyme elevation and normal electrolyte and hematology screens, thyroid function and coagulation profile. Lyme antibody screen drawn one week prior to admission was positive at 4.61. Quantitative Lyme IgM by EIA was positive at 2.46. Western blot analysis was positive for Lyme IgG with 10 of 10 banding patterns matching.
She was admitted to a monitored bed and treated with intravenous ceftriaxone 2 gm daily and oral prednisone 60 mg daily. Her heart rhythm continued to fluctuate between second degree 2:1 AV block and complete heart block. An electrophysiology study revealed the AV block to be at the level of the AV node and the patient had normal His-Purkinje function. The patient’s HV interval was 40 milliseconds. Within days of treatment, her symptoms improved and her electrocardiogram had improved to first-degree AV block (Figure 2). She was discharged after an uncomplicated hospital stay home to complete a three-week course of intravenous ceftriaxone. She subsequently had complete resolution of her AV conduction disorder and symptoms. Figure 3 shows the electrocardiogram six months after treatment.
The cardinal manifestation of Lyme carditis is conduction system disease. Myocardial and pericardial involvement can occur, but is generally mild and self-limited.2 Fluctuating degrees of AV block, occasional acute myopericarditis or mild left ventricular dysfunction and rarely cardiomegaly or fatal pericarditis have been known to occur. The only reported chronic manifestation of Lyme disease is of a chronic dilated cardiomyopathy.3
Cardiovascular manifestations are acute, often occurring within 21 days of exposure, and most commonly result in second- or third-degree AV block that resolve spontaneously within days or weeks.4 Heart block occurs usually at the level of the atrioventricular node, but is often unresponsive to atropine sulfate.2 Temporary pacing may be necessary in more than 30% of patients, but permanent heart block rarely develops.2
Diagnosis of Lyme carditis is based on the clinical history and symptoms and exposure to an endemic region and the only definitive test for diagnosing Lyme carditis is by histopathology. Most patients will be able to recollect a tick bite, but the typical erythema chronicum migrans will appear in 60–80% of cases. Laboratory diagnosis includes isolation of Borrelia Burgdorferi from a Barbour–Stoenner–Kelly medium. Serological laboratory tests include enzyme-linked immunosorbent assays for IgG and IgM to Borrelia Burgdorferi followed by a confirmatory western blot. The diagnosis of Lyme disease can also be made by the polymerase chain reaction (PCR), but this method has not been standardized for routine diagnosis of Lyme disease.5
An echocardiogram is likely to yield normal myocardial function in acute Lyme disease. Slight nonspecific pericardial effusions have been noted in European patients with Lyme disease.6 However, in chronic Lyme carditis or patients with long-standing untreated disease, echocardiography is a useful tool in diagnosing and monitoring treatment in dilated cardiomyopathy secondary to Lyme disease.7
Cardiac troponin levels are useful in diagnosing the rare cases of Lyme myocarditis and myopericarditis. Cardiac enzymes are not elevated in the majority of cases of Lyme carditis in which only atrioventricular block are present.
All symptomatic patients with presumptive or definitive diagnosis of Lyme carditis will need effective intravenous antibiotic treatment. Patients with first- or second-degree AV block can be treated with an oral antibiotic regimen for 14–21 days. Patients with third-degree AV block or pauses need to be treated with intravenous ceftriaxone for 14–21 days.8 Most patients will have symptomatic improvement within 7 days of starting antibiotics (Table 1).
Patients with suspected or known Lyme disease presenting with cardiac symptoms, or patients in an endemic area presenting with cardiac symptoms with no other cardiac risk factors should have a screening electrocardiogram along with Lyme titers. Patients with suspected Lyme carditis require hospitalization for cardiac monitoring. They usually exhibit symptoms of dizziness, dyspnea on exertion, palpitations or syncope, primarily due to varying degrees of AV block. Patients that fluctuate between third degree and asystolic pauses will require temporary transcutaneous or transvenous pacing. Symptoms and the electrocardiogram usually improve with proper antibiotic treatment, and do not usually require the implantation of a permanent cardiac pacemaker. The case presented highlights the typical findings of AV block secondary to Lyme disease and demonstrates total reversibility after a complete course of antibiotics.