Lyme disease is the most common of tick-borne illnesses in the United States. One of the complications is carditis, which reportedly ranges between 1 and 10 % of the total Lyme disease cases. It presents in the early disseminated stage, the second phase of the disease. The most prominent manifestations are conduction system disturbances involving the atrioventricular (AV) node. This affection leads to several degrees of heart block that in some cases require the placement of a temporary pacemaker.
Other forms of presentation include myocarditis, endocarditis, valvular heart disease, pericarditis, and myopericarditis. However, such conditions have been reported less frequently than the typical conduction system abnormalities.
Lyme disease results from infection with the spirochete Borrelia burgdorferi (B.burgdorferi), named in honor of the microbiologist Dr. Willy Burgdorfer who isolated it in 1982. The natural reservoir for the spirochete includes mice, chipmunks, and other small mammals. Deer are not competent hosts for B.burgdorferi, but they play an important role in sustaining the life cycle of the vector, Ixodes tick, which transmits the spirochete. This tick acquires B.burgdorferi by feeding on an infected animal and may transmit the infection to a human during a subsequent blood meal.
Approximately 30000 cases of Lyme disease are reported annually in the United States; however, the real number can be much higher. In 2015, 95% of cases identified were in the Northeast, mid-Atlantic and upper Midwest states, and the most affected groups were males between 5 and 9 and 45 to 59 years old. Lyme disease is diagnosed most commonly between March and October with 60% in June and July. Cardiovascular symptoms are present in approximately 1.5% to 10% of reported cases in the United States. Cases have also been found to be more common in young adult males with a roughly 3 to 1 male: female ratio.
Replication of B. burgdorferi happens at the site of its inoculation after the tick bite. Following this incident, in a period ranging from few days to a month, the innate and adaptive cellular immune response arises locally at the site of spirochete entry. After these events, the spirochete, with the help of several body’s proteins and other substances, spreads to other tissues including the central nervous system, eye, muscle, liver, spleen, and the heart.
The immune response activates before and during the organism dissemination. In an attempt to stop this invasion, the body initially activates B-Cell clones with subsequent elevation of IgM levels. Weeks to months later, production of IgG directed to different components of B. burgdorferi induces complement fixation and opsonization with consequent bactericidal killing.
The exact mechanism leading to cardiac manifestations is not entirely understood. However, it seems to be an autoimmune inflammatory response to the spirochetes present in heart tissue, which causes the abnormalities inducing AV block. It is possible that cross-reactive IgM antibodies can react with cardiac tissue with consequent injury and functional abnormalities. Researchers have also noted that there is a strong correlation between the number of spirochetes in heart tissue, myocardial inflammation, and the degree of conduction abnormalities.
Pathophysiologic events causing Lyme endocarditis are even less clear. No microorganisms usually appear in tissue samples; for this reason, diagnostic confirmation is by other means including serologic tests and polymerase chain reaction (PCR)
The characteristic histopathological finding is an interstitial inflammatory infiltrate containing lymphocytes, histiocytes, and plasma cells. Such infiltrate extends from the endocardium to the epicardium. Neutrophils and eosinophils do not appear in a substantial amount. Spirochetes have been visualized in the epicardium, myocardium, and endocardium with the use of Warthin-Starry stain and also by immunohistochemistry. However, B.burgdorferi is not always identified. In some case reports of Lyme endocarditis, bacteria appear absent in tissue samples and, other diagnostic methods, such as polymerase chain reaction (PCR), have been required to confirm such condition.
Lyme carditis must be a consideration in patients with the typical clinical manifestations of Lyme disease, which usually occurs in various stages. The first phase, early localized infection, is recognized by the characteristic erythema migrans. Following the local manifestation, patients may develop generalized symptoms such as malaise, fever and chills, headache, myalgias, arthralgias, and dizziness as the spirochete continues spreading. It is at this time that cardiac manifestations can arise. Most cases of Lyme carditis occur between June and December. Symptoms are developed from four days up to seven months after initial presentation (such as a rash) with a median of 21 days. Patients may initially present the characteristic signs and symptoms of the disease; however, reports exist indicating that many patients do not recall a tick bite and, the typical rash is present in only 40% of patients with Lyme carditis. The most common symptoms are related to the most common cardiac manifestations such as heart block, light-headedness, syncope, shortness of breath, palpitations, and/or chest pain.
Cases of endocarditis with valvular involvement, pericarditis, and myocarditis attributed to Lyme disease have also appeared in the literature. However, these manifestations are reported less commonly than the characteristic conduction delayed abnormalities.
Cases of myopericarditis present with symptoms and electrocardiographic changes similar to acute coronary syndrome; 60% of those patients will present with T wave inversion or ST-segment depression. It is rare to find patients with high troponin levels and/or ST-segment elevation. Valvular involvement with endocarditis is not common; if that is the case, patients usually exhibit signs of acute heart failure and cardiogenic shock.
Atrioventricular block (AV block) of varying degree is the most frequent manifestation of Lyme carditis. Therefore, if a patient presents with the characteristic demographic and clinical manifestations, including bradycardia, the next step is to carefully evaluate an electrocardiogram (ECG). AV block in Lyme carditis may range from first degree to complete heart block, also known as third-degree AV block. In these patients, the degree of AV block may change over minutes, hours, or days.
AV block denotes an abnormal relationship between the P wave and QRS complex. First-degree AV block characteristically demonstrates a fixed prolongation of the PR interval (greater than 200 milliseconds). Second-degree AV block displays a progressive prolongation of the PR interval followed by a nonconductive P wave (Mobitz type I) or presents with an unchanged PR interval followed by a single non-conducted P wave (Mobitz type II). In the highest degree of AV block, third degree, there is no atrioventricular conduction, and the ECG shows a dissociation between P waves and QRS complexes. Additional studies are not usually necessary if heart block is the only manifestation of Lyme carditis.
Supplementary studies play a more important role when suspecting valvular disease or myocarditis. A chest X-ray may show bilateral infiltrates or pleural effusions. Echocardiography may show mild left ventricular or right ventricular dilation in cases with predominant conduction abnormalities. However, most of the time the ventricle size remains preserved. Echocardiography may also play a role in differentiating myocarditis from myocardial infarction. In patients with signs and ECG changes characteristics of the acute coronary syndrome, echocardiography reveals diffuse ventricular hypokinesis as opposed to focal wall motion abnormalities seen in myocarditis. If difficulty in differentiating between these two conditions is present, cardiac MRI merits consideration. In myocarditis, cardiac MRI may show areas of increased epicardial contrast enhancement with no subendocardial involvement as seen in acute coronary syndrome.
The gold standard to diagnose infectious diseases continues to be the isolation of the offending pathogen; this is not the case of B. burgdorferi which, like some other spirochetes, cannot be cultivated. The diagnosis is based on indirect serologic tests in addition to clinical suspicion and supporting laboratory and imaging tests. In many cases, clinical suspicion alone may warrant antibiotic treatment. However, many patients may not present the typical manifestations or symptoms may be ambiguous. A two-step method of serologic testing is suggested as the approach to follow. Enzyme-linked immunosorbent assay (ELISA) is the first test to be considered. If IgM or IgG is positive or borderline, Western Blot assay is required to confirm the diagnosis. Also, B. burgdorferi DNA has been detected in heart tissue by PCR. PCR is an optino if the suspected cause of myocarditis or endocarditis is Lyme disease, and if the serologic tests for this condition are negative or equivocal when the suspicion is high.
Even though some cases of Lyme carditis can resolve without treatment, antibiotics are indicated to lower the risk of cardiovascular complications, avoid sequela, and shorten the duration of the disease. Beta-lactam antibiotics with demonstrated effectiveness against B. burgdorferi include cephalosporins and tetracyclines. For mild to moderate disease, oral amoxicillin or doxycycline is indicated for 14 to 21 days.
Patients with more severe disease require hospitalization. Criteria to admit patients include:
1) Presence of symptoms such as syncope, dyspnea or chest pain
2) AV block of the second or third-degree
3) AV block of first degree with P-R interval greater than or equal to 300 ms.
Although there is no evidence indicating the superiority of treatment with parenteral over oral antibiotics, parenteral treatment is the general recommendation for initial treatment in hospitalized patients. Ceftriaxone or cefotaxime is the usual recommended parenteral antibiotics. Intravenous antibiotics should continue until the resolution of second or third-degree AVB or until the P-R interval shortens to under 300 ms. Patients may later continue oral therapy to complete a complete course of 14 to 21 days.
Temporary pacemaker placement is indicated in patients with a combination of hemodynamic instability and high-grade second or third-degree AVB to avoid. The pacemaker can be removed once the high degree heart block has resolved.
Since conduction disturbances are transient, resolve with antibiotic treatment, and are not expected to recur, permanent pacemaker placement is not a recommendation. The 2008 American College of Cardiology/American Heart Association/Heart rhythm society Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities points Lyme carditis out as a class 3 indication.
Lyme carditis generally has a good prognosis. It is usually associated with conduction disturbances and is, most of the time, a treatable condition. With adequate antibiotic treatment, the recovery time of patients with third-degree heart block has a median of six days. Some cases of persistent AV block exist, but they are extremely rare. There are reports of death secondary to severe myocarditis. However, there are only a few documented cases with this outcome.
Reports exist of fatal cases; nevertheless, the mortality rate associated with Lyme carditis has always been low and has declined even more as early identification and subsequent antibiotic treatment has improved over time. There was a published report of three deaths associated with Lyme carditis in 2013. After this publication, the CDC directed a follow-up investigation, which included 1696 cases reported between 1995 and 2013. Of the three cases, only two were confirmed as Lyme carditis-associated mortality, this account for 0.001% of the total.
If traveling to endemic areas, minimizing the contact with tick can be achieved by:
Antibiotic prophylaxis with oral doxycycline 200 mg is the recommended course for individuals with tick attachment for at least 36 hours.
Medical evaluation is necessary for people who develop a rash in the site of tick attachment, multiple skin lesions, or generalized flu-like symptoms.
Patients with Lyme disease, in general, are managed by an interprofessional team because of its diverse presentation and difficulty in diagnosis. The majority of cases are manageable by the primary caregiver, nurse practitioner, and internist as part of an interprofessional team. However, Lyme carditis is best managed by an infectious disease expert and a cardiologist. While the condition usually resolves, close monitoring is necessary as some patients may require temporary pacing.
Lyme disease is best prevented. Primary care clinicians and nurses should work together to provide patient and family education in endemic areas.
Even though Lyme carditis occurs in only a small percentage of patients with Lyme disease, significant consequences can develop. Thus, people going to or living in endemic areas require education regarding protective measurements. Hikers should wear appropriate garments and know how to remove the tick.
If symptoms develop, immediate medical evaluation and assistance is a prudent course of action. Medical providers must have a high clinical suspicion of the disease taking into account epidemiological risk factors. If the suspicious index is high, further serologic testing is necessary for confirmation. Prompt treatment is required in established cases as resolution rate is high if actions take place with no delay.
A team approach to Lyme carditis can greatly facilitate diagnosis and help prevent complications. The infectious disease specialist and cardiologist should work collaboratively, and keep the family physician in the loop. Nursing will administer IV antibiotics and monitor treatment progression, vital signs, and potential mediation adverse effects, and report any status changes to the physician in charge. The pharmacist will verify all dosing, check agent selection against antibiograms, and perform medication reconciliation to avoid drug-drug interactions, communicating to the team regarding any concerns that may arise. Nursing will be responsible for monitoring the patient, assessing compliance with therapy, answering patient questions, and reporting their findings back to the team. Only with this type of interprofessional team approach can cases of Lyme carditis be expected to achieve optimal outcomes. [Level 5]
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