A 36-Year-Old Man Comes to the Emergency Department After Briefly

A 36-year-old man comes to the emergency department after briefly losing consciousness while watching television half an hour ago.  The patient had no preceding chest pain or shortness of breath, but he has been having recurrent palpitations over the past several days.  Two weeks ago, he noticed a non-itchy rash on his thigh that he treated with an over-the-counter steroid cream.  Medical history is otherwise unremarkable.  There is no family history of heart disease or sudden cardiac death.  The patient recently began working as a forest ranger in Pennsylvania.  He does not use tobacco, alcohol, or illicit drugs.  Blood pressure is 130/80 mm Hg and pulse is 46/min.  The lungs are clear on auscultation and heart sounds are normal.  The remainder of the examination shows no abnormalities.  ECG reveals complete atrioventricular block.  Echocardiography shows normal ventricular function with no major valvular disease.  Which of the following is the most likely underlying cause of this patient's current condition?

A) Disseminated spirochetal infection
B) Granulomatous myocardial inflammation
C) Missense mutation of a sarcomere protein
D) Myocyte potassium channel mutation
E) Viral infection-induced cardiac injury

Correct Answer:

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