TAILIEUCHUNG - Chapter 021. Syncope

Presyncopal symptoms vary in duration and may increase in severity until loss of consciousness occurs, or they may resolve prior to loss of consciousness if the cerebral ischemia is corrected. The differentiation of syncope from seizure is an important, sometimes difficult, diagnostic may be benign when it occurs as a result of normal cardiovascular reflex effects on heart rate and vascular tone, or serious when due to a life-threatening cardiac arrhythmia. | Chapter 021. Syncope Presyncopal symptoms vary in duration and may increase in severity until loss of consciousness occurs or they may resolve prior to loss of consciousness if the cerebral ischemia is corrected. The differentiation of syncope from seizure is an important sometimes difficult diagnostic may be benign when it occurs as a result of normal cardiovascular reflex effects on heart rate and vascular tone or serious when due to a life-threatening cardiac arrhythmia. Syncope may occur as a single event or may be recurrent. Recurrent unexplained syncope particularly in an individual with structural heart disease is associated with a high risk of death 40 mortality within 2 years . Pathophysiology Under normal circumstances systemic blood pressure is regulated by a complex process that includes the musculature venous valves autonomic nervous system and renin-aldosterone-angiotensin system. Knowledge of these processes is important to understanding the pathophysiology of syncope. Approximately three-fourths of the systemic blood volume is contained in the venous bed and any interference in venous return may lead to a reduction in cardiac output. Cerebral blood flow can be maintained if cardiac output and systemic arterial vasoconstriction compensate but when these adjustments fail hypotension with resultant cerebral underperfusion to less than half of normal results in syncope. Normally the pooling of blood in the lower parts of the body is prevented by 1 pressor reflexes that induce constriction of peripheral arterioles and venules 2 reflex acceleration of the heart by means of aortic and carotid reflexes and 3 improvement of venous return to the heart by activity of the muscles of the limbs. Tilting a normal person upright on a tilt table causes some blood to accumulate in the lower limbs and diminishes cardiac output slightly this may be followed by a slight transitory fall in systolic blood pressure. However in a patient with defective .

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