Near syncope is a feeling of light-headedness, which, in its most severe form, leads to loss of consciousness (syncope). Some patients with near syncope may refer to the sensation of light-headedness as dizziness. Syncope and near syncope differ only in their severity. The most common categories of near syncope are vasovagal, situational, orthostatic hypotension, and drug-induced syncope. Cardiac causes such as valvular heart disease as well as cardiac dysrhythmias are also significant causes. The cause of near syncope is not determined in a significant percentage of patients. Recent evidence suggests that the majority of patients with unexplained presyncope may have vasovagal presyncope. Sole reliance on the typical clinical presentation of vasovagal presyncope may lead to underdiagnosis. Positive upright tilt testing, in which the patient is placed in the passive upright position at 60° for 45 min, is generally recommended. 12 Some protocols involve the use of isoproterenol. The end points of a positive tilt test include the development of syncope or presyncope associated with hypotension, bradycardia, or both. In normal subjects, tachycardia usually results from a passive tilt test.11
Syncope and near syncope in the elderly are associated with daily events, including micturition, defecation, postural changes, meals, laughing, coughing, and swallowing. Orthostatic hypotension is extremely common in the elderly and is associated with volume depletion, venous insufficiency, poor conditioning, polyneuropathy, preganglionic autonomic dysfunction (Shy-Drager syndrome), as well as the use of medications including vasodilating drugs, diuretics, other antihypertensive agents, and antiparkinsonian and anticholinergic medications. According to a position paper by the American College of Physicians, syncope in the elderly often results from polypharmacy and abnormal responses to daily events.
A new diagnostic entity has emerged called postural orthostatic tachycardia syndrome. This is a relatively mild disorder associated with a fall in blood pressure in which patients experience near-syncope, nonvertiginous dizziness, and symptoms suggestive of TIA. This condition may involve less dramatic falls in blood pressure than those seen in syncope. The pathogenesis is thought to be mild autonomic dysfunction. Findings on tilt testing include an increase in heart rate of 30 beats per minute over baseline within the first 10 min of testing (unassociated with profound hypotension), along with recurrence of the symptom complex.12
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