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Chapter 90: Diagnosis and Management of Syncope

Obstructive cardiac disorders associated with syncope include all of the following except:

A. Pulmonary embolism

B. Hypertrophic cardiomyopathy

C. Atrial myxoma

D. Cardiac tamponade

E. Supraventricular tachycardia

The answer is E. (Hurst’s The Heart, 14th Edition, Chap. 90) Obstruction to cardiac output in the left or right side of the heart may cause syncope. The relationship of syncope to exertion may provide clues to the etiology. Loss of consciousness during or immediately after exertion can occur with any of the cardiac causes of syncope, but it is particularly common and may be the presenting symptom in patients with certain obstructive lesions, including aortic stenosis and hypertrophic cardiomyopathy (option B). Studies suggest that in such patients, the failure of cardiac output to increase adequately during exercise together with a reflex decrease in peripheral vascular resistance may play a role.1 Nonexertional syncope related to acute decreases in preload or afterload or to inotropic stimulation may also occur in either aortic stenosis or hypertrophic cardiomyopathy. Other cardiac disorders associated with syncope include mitral stenosis, typically in the setting of tachycardia or other arrhythmia, atrial myxoma (option C), obstruction in the pulmonary vasculature as a result of pulmonary artery hypertension, pulmonary stenosis, or pulmonary embolism (option A), cardiac tamponade (option D) which affects both the right and left sides of the heart, tetralogy of Fallot, and prosthetic mitral or aortic valve malfunction.

A 70-year-old woman presents after experiencing her third syncopal episode in the last year. The syncopal events always occur upon standing from a seated position. Which of the following does not occur immediately upon standing from a supine position?

A. Approximately 300 to 800 mL of blood is displaced to the lower limbs and the inferior mesenteric area

B. There is a mean decrease in stroke volume of approximately 40% within the first few seconds of standing

C. The discharge rate of the aortic arch and carotid sinus baroreceptors is increased

D. A decrease in efferent vagal activity is observed, with an increase in efferent sympathetic activity

E. A 10 to 15 bpm increase in heart rate is observed, with an approximately 10 mm Hg increase in diastolic blood pressure

The answer is C. (Hurst’s The Heart, 14th Edition, Chap. 90) In the normal supine individual, approximately one-quarter of the blood volume is in the thorax. On standing, there is a gravity-mediated displacement of between ...

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