What Are The Cardiac Findings In Lyme Disease?

Lyme disease is caused by the tick-borne spirochete, Borrelia burgdorferi. The initial infection is often marked by a rash, followed in weeks to months by involvement of other organ systems, including the heart, neurologic system, and joints. About 1 in 10 patients manifest cardiac involvement, usually with severe atrioventricular (AV) node block which is often associated with syncope, since there is concomitant depression of ventricular escape rhythms. Temporary pacing is indicated (the AV block usually resolves), as is antibiotic treatment with high-dose intravenous penicillin or oral tetracycline.

How long after the initial infection with Trypanosoma cruzi (Chagas' disease) do the cardiac manifestations occur?

The initial infection with Trypanosoma occurs when young adults are bit, usually around the eye, by a reduviid bug.

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A few individuals (about 1%) develop an acute myocarditis and pericarditis, which usually resolves over time. The major cardiac manifestation of Chagas' disease occurs about 20 years after the initial infection and is evident in 30% of the infected subjects. It involves cardiomegaly, congestive heart failure, arrhythmias, thromboembolism, right bundle branch block, and sudden death.

What are some unusual features of the cardiac involvement in Chagas' disease?

The pathologic appearance shows infiltration followed by fibrotic changes. There is a characteristic involvement of the right ventricle early in the process, which explains the early manifestations of right heart failure and tricuspid insufficiency. There is a predilection for involvement of the right bundle branch with subsequent right bundle branch block and an associated left anterior hemiblock. The fibrosis often extends into the apex of the left ventricle, resulting in a thin-walled, thrombus-filled ventricular aneurysm.

Laboratory and noninvasive testing yields in some characteristic findings. The ECG shows characteristic right bundle branch block and left anterior hemiblock. ST and T-wave changes may be present. Ventricular arrhythmia's are common, especially following exercise. Electrophysio-logic testing often demonstrates inducible ventricular tachycardia. Echocardiography may demonstrate apical akinesia or a frank apical aneurysm, often with a ventricular thrombus. This pathophysiology explains the high incidence of sudden death and thromboembolic phenomena (seen in 50% of patients).

Describe the cardiac manifestations of a pheochromocytoma.

Patients may present with a reversible dilated cardiomyopathy. The cause is assumed to be the high level of circulating catecholamines resulting from the tumor, which may result in cell damage via a variety of pathways. The protective effect of aspirin suggests a role for platelet aggregation.

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