What is the most common cardiac manifestation of Lyme disease?

The most common cardiac manifestation of Lyme disease is indeed an atrioventricular (AV) conduction block. Lyme disease, caused by the spirochete Borrelia burgdorferi, can lead to a variety of clinical manifestations, including those affecting the heart. While myocarditis, pericardial effusion, and arrhythmias can occur as manifestations of Lyme disease, they do not present as frequently or characteristically as AV conduction abnormalities.

Specifically, the AV block seen in Lyme disease is often a first-degree or, more notably, a high-degree AV block that can result in bradycardia or syncope. This occurs as the spirochete affects the cardiac conduction system, leading to impaired electrical conduction. The presence of an AV block in a patient with Lyme disease usually indicates a more severe or systemic form of the disease, emphasizing the need for timely treatment with appropriate antibiotics to prevent further complications.

Overall, the predominance of AV conduction defects in Lyme disease underscores the importance of recognizing the signs and symptoms of this illness in patients presenting with relevant clinical features, such as the characteristic erythema migrans rash, joint pain, or neurological symptoms, in order to provide effective management and prevent serious cardiac complications.