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 follovving is the most
likely earliest site of electric activation?
Q A. Junction of left atrium and atrial appendage
Q 8. Left atrium near the opening of pulmonary veins
Q C. Right atrium near the opening of inferior vena cava
Q D. Right atrium near the opening of superior vena cava Q E. Right atrium near the septa! cusp of tricuspid valve