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?

Question

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?

Quizplus · Accepted Answer

11ec160b_3566_bf68_9249_99314ee4bde2_MD0001_00 The cardiac conduction system consists of the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, right and left bundle branches, and the Purkinje system (which directly activates the ventricular myocardium). In patients with normal sinus rhythm (as in this patient), the SA node acts as the dominant pacemaker site and is the site of earliest electrical activation. The SA node is a compact subepicardial structure that consists of specialized pacemaker cells located at the junction of the right atrium and superior vena cava. (Choices A and B) The SA node is located in the right, not the left, atrium. The area around the opening of the pulmonary veins in the left atrium is frequently involved in the pathogenesis of atrial fibrillation. (Choice C) The junction of the right atrium and inferior vena cava is not a major site of electrical activity. (Choice E) The AV node is located in the right atrium near the septal cusp of the tricuspid valve. Educational objective: The sinoatrial node consists of specialized pacemaker cells located at the junction of the right atrium and superior vena cava. It is the site of earliest electrical activation in patients with sinus rhythm. __________ References: The sinoatrial node, a heterogeneous pacemaker structure. (http://www.ncbi.nlm.nih.gov/pubmed/10974216) The anatomy of the cardiac conduction system. (http://www.ncbi.nlm.nih.gov/pubmed/18773472)

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