<p><strong>OBJECTIVE: </strong>To examine the association between electrocardiographic (ECG) evidence of carditis at the time of Lyme disease evaluation and a diagnosis of Lyme disease.</p>

<p><strong>STUDY DESIGN: </strong>We performed an eight-center prospective cohort study of children undergoing emergency department evaluation for Lyme disease limited to those who had an ECG obtained by their treating clinicians. The study cardiologist reviewed all ECGs flagged as abnormal by the study sites to assess for ECG evidence of carditis. We defined Lyme disease with the presence of an erythema migrans lesion or a positive two-tier Lyme disease serology. We used logistic regression to measure the association between Lyme disease and AV block or any ECG evidence of carditis.</p>

<p><strong>RESULTS: </strong>Of the 546 children who had an ECG obtained, 214 (39%) had Lyme disease. Overall, 42 children had ECG evidence of carditis of which 24 had atrioventricular (AV) block (20 first degree). Of the patients with ECG evidence of carditis, only 21 (50%) had any cardiac symptoms. The presence of AV block (odds ratio 4.7, 95% confidence interval 1.8-12.1) and any ECG evidence of carditis (odds ratio 2.3, 95% confidence interval 1.2-4.3) were both associated with diagnosis of Lyme disease.</p>

<p><strong>CONCLUSIONS: </strong>ECG evidence of carditis, especially AV block, was associated with a diagnosis of Lyme disease. ECG evidence of carditis can be used as a diagnostic biomarker for Lyme disease to guide initial management while awaiting Lyme disease test results.</p>