Harrison's Internal Medicine Chapter 21. Syncope Syncope: Introduction Syncope, a transient loss of consciousness and postural tone due to reduced cerebral blood flow, is associated with spontaneous recovery. It may occur suddenly, without warning, or may be preceded by symptoms of faintness ("presyncope"). These symptoms include lightheadedness, dizziness, a feeling of warmth, diaphoresis, nausea, and visual blurring occasionally proceeding to transient blindness. 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. | Chapter 021. Syncope Part 1 Harrison s Internal Medicine Chapter 21. Syncope Syncope Introduction Syncope a transient loss of consciousness and postural tone due to reduced cerebral blood flow is associated with spontaneous recovery. It may occur suddenly without warning or may be preceded by symptoms of faintness presyncope . These symptoms include lightheadedness dizziness a feeling of warmth diaphoresis nausea and visual blurring occasionally proceeding to transient blindness. 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 problem. Syncope 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 .
