Although the patient could not recall any recent tick exposure, she lived in an area endemic for Lyme disease, and reported being outdoors for much of each day. The diagnosis of Lyme carditis was made, she was started on ceftriaxone for presumed disseminated Lyme disease, and she was admitted to the pediatric ICU for monitoring.
Lyme borreliosis is the most common tickborne disease in the United States. It is caused by the spirochete Borrelia burgdorferi, and is transmitted by the common deer tick. The species of deer tick varies by location with Ixodes scapularis being found in the mid-Atlantic states and Ixodes pacificus on the West Coast. The vast majority of reported cases of Lyme disease are from northeastern states such as Connecticut, Rhode Island, New York, Massachusetts, and Pennsylvania or from the upper Midwest. In 2003, the federal Centers for Disease Control and Prevention reported more than 20,000 cases in the contiguous 48 states.
Of those infected, approximately 10 percent will develop cardiac manifestations. Cardiac involvement typically occurs during the early disseminated phase of the infection. Manifestations range from asymptomatic first-degree heart block to complete heart block, and rarely, dilated cardiomyopathy. The conduction abnormalities can occur concomitantly with other signs and symptoms of disseminated disease including neurologic involvement such as a facial nerve palsy or the classic erythema migrans rash. Alternatively, these cardiac manifestations can be the first and only sign of infection. When cardiac involvement does occur, it is not uncommon to have mild and self-limited myocardial involvement. This manifests as subtle and nonspecific ST-T wave abnormalities on the ECG.
Common symptoms include palpitations, dizziness, shortness of breath, and fatigue. Syncope is not uncommon in those who progress to complete heart block.
The diagnosis of Lyme carditis can be relatively straightforward when new onset conduction abnormalities occur simultaneously with other signs and symptoms of disseminated Lyme disease, as was the case with this patient. If the cardiac manifestations occur in isolation, however, a high index of suspicion is necessary to make the diagnosis. The diagnosis can be confirmed by serology testing using ELISA or Western blot analysis, but it is important to point out that serology testing will be negative during the first several weeks of infection. Eliciting a history of tick exposure, erythema migrans rash, or outdoor activities in an endemic area is important when considering the diagnosis.
Although any area of the conduction system can be affected, the most common presentation is a first-degree AV block. One of the hallmarks of Lyme carditis is the rapidity with which the conduction abnormalities can change. It is not uncommon to see several different degrees of AV block within a relatively short period of time. It is estimated that approximately 50 percent of patients with Lyme carditis will develop complete heart block during the course of their disease. (Clin Pediatr Emerg Med 2004;5.) Those with a markedly prolonged PR interval (≥300 ms) seem to be at the greatest risk for progression to complete heart block. The ECGs shown here were all recorded from another of our patients with Lyme carditis over a period of only 24 hours. (Figures 3–5.) This patient was a 58-year-old man who presented with atypical chest pain, no rash, and no known tick exposure. The diagnosis was confirmed by serologic testing, and he recovered completely.
Once the diagnosis of Lyme carditis is made, antibiotics effective against Borrelia burgdorferi should be initiated. Although there is good evidence that disseminated Lyme disease should be treated with parenteral antibiotics, there is no consensus regarding treatment for isolated Lyme carditis. The Infectious Diseases Society of America recommends oral therapy with doxycycline or amoxicillin for asymptomatic 1st or 2nd degree heart block. Furthermore, there is no evidence that treatment with antibiotics alters the course of the conduction abnormalities seen in Lyme carditis. It seems prudent in patients with high-grade AV block caused by Lyme disease, however, that parenteral antibiotic therapy should be administered in a monitored setting.
Parenteral antibiotic choices include ceftriaxone 2 g QD, cefotaxime 2 g BID, or penicillin G 200,000 to 400,000 units/kg/day divided into six doses. Duration of treatment for disseminated disease should be for four weeks. Oral regimens include doxycycline 100 mg BID or amoxicillin 500 mg TID with treatment durations ranging from 14 to 21 days. (Clin Infect Dis 2000;31(Suppl: 1):S1–14.)
Symptomatic patients should be admitted to a monitored bed during initiation of therapy due to the potential of rapid progression to a high-grade block. It is worth noting that bradycardia in patients with complete heart block typically will not respond to atropine, and temporary pacing may be necessary.
The prognosis for patients with Lyme disease and cardiac involvement is very good. Most conduction abnormalities will resolve within three to six days. Occasionally a persistent 1st degree AV block persists for several months after treatment, but these are typically well tolerated and also will resolve spontaneously. Very rarely, patients can have a persistent high-grade block that necessitates pacemaker placement. There have been case reports of dilated cardiomyopathy secondary to Lyme myocarditis, but these appear to be extremely rare and respond well to appropriate therapy.
Although this case was a relatively straightforward diagnosis given the multiple erythema migrans lesions in a new conduction abnormality in a young woman who resided in an area endemic for Lyme disease, Lyme carditis often can present a challenging diagnostic dilemma, particularly when the cardiac manifestations of this infection present in isolation. A thorough history focusing on risk factors and subtle symptoms combined with a high index of suspicion is necessary for any patient who presents with a newly diagnosed heart block.© 2005 Lippincott Williams & Wilkins, Inc.