A 35-Year-Old Previously Healthy Man Is Evaluated for Several Episodes

A 35-year-old previously healthy man is evaluated for several episodes of syncope in the past 6 weeks.  Physical examination is unremarkable.  Echocardiogram shows no structural heart defect.  An electrophysiologic study is performed during which catheters are passed into the patient's right and left atrium to record atrial electric potentials.  Cardiac monitor currently shows normal sinus rhythm.  Which of the following is the most likely earliest site of electric activation?

A) Junction of left atrium and atrial appendage
B) Left atrium near the opening of pulmonary veins
C) Right atrium near the opening of inferior vena cava
D) Right atrium near the opening of superior vena cava
E) Right atrium near the septal cusp of tricuspid valve

Correct Answer:

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