syncope

syncope Partial or complete loss of consciousness, with interruption of awareness of self and surroundings and spontaneous recovery that is due to a temporary reduction in blood flow and therefore a shortage of oxygen to the brain. This leads to lightheadedness or a “blackout” episode (loss of consciousness). Heart conditions that can cause syncope include abnormal heart rhythms, abnormalities of the heart valves, high blood pressure in the arteries supplying the lungs (pulmonary artery hypertension), tears in the aorta (aortic dissection), and widespread disease of the heart muscle (cardiomyopathy). However, syncope is most commonly caused by conditions that do not directly involve the heart, including postural (orthostatic) hypotension, a drop in blood pressure due to changing body position to a more vertical position after lying or sitting; dehydration, which can cause a decrease in blood volume; blood pressure medications that lead to overly low blood pressure; diseases of the nerves to the legs which can dilate blood vessels in the legs and reduce blood flow to the heart; high altitude; stroke or transient ischemic attack; and migraine attack. Another common form of noncardiac syncope is known as situational syncope because the fainting occurs after certain situations. Triggers for situational syncope include having blood drawn, urinating (micturition syncope), defecating (defecation syncope), swallowing (swallowing syncope), and coughing (cough syncope). In some individuals, one or more of these situations can trigger a reflex of the involuntary nervous system called the vasovagal reaction, which slows the heart, dilates blood vessels in the legs, and causes the person to feel nausea, sweating, or weakness just before fainting. No treatment is needed for many noncardiac causes of syncope, as the person regains consciousness by simply sitting or lying down. Also known as fainting. See also syncope, situational; vasovagal reaction.