TABLE 31-1A Causes of Syncope | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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TABLE 31-1B Causes of Non-syncopal Attacks (Often Confused with Syncope) |
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Syncope
Syncope
Adam S. Fein
Karen E. Thomas
I. GENERAL PRINCIPLES
A. Definition: sudden, transient loss of consciousness (TLOC) with loss of postural tone.
II. PATHOPHYSIOLOGY
A. Caused by transient hypoxia and/or hypoperfusion of the cerebral cortices and reticular activating system due to low peripheral resistance and/or low cardiac output.
B. Systolic blood pressure <70 mm Hg or interruption of cerebral blood flow for 8 to 10 seconds usually results in syncope.
C. Pathophysiologic mechanisms potentiating syncopal events are commonly divided into (a) reflex (neutrally mediated) with both vasodepressor and cardioinhibitory effects, (b) orthostatic hypotension with low peripheral resistance and poor venous return, and (c) cardiac causes with insufficient cardiac output.
D. Syncope is one of numerous causes of TLOC. Epileptic seizures, which cause loss of consciousness (LOC) through global interruption of cerebral electrical activity without necessarily impairing blood flow, are another. See Tables 31-1A and 31-1B for causes of LOC.
III. ETIOLOGY
A. Differential diagnosis.
1. The causes of syncope can be classified by etiology and pathophysiology. Please see Table 31-1A.
2. Neurocardiogenic syncope and orthostatic intolerance are most common. Neurologic, cardiovascular, and psychogenic pseudosyncope causes occur with decreasing frequency.
3. Up to 41% of patients will have “syncope of unknown cause” despite a thorough evaluation.
4. Prognosis is related to the severity of underlying disease, with mortality worse in patients with structural cardiac disease. Syncope of cardiac etiology, in the absence of implantable defibrillator, has 1-year mortality of 20% to 30% compared to 0% to 12% for patients with noncardiovascular causes of syncope and 6% for those with syncope of unknown etiology.
5. Younger patients more frequently have syncope due to noncardiovascular cause or syncope of unknown origin and overall have a more favorable prognosis. Older patients more often have a cardiac etiology or syncope due to polypharmacy.
IV. DIAGNOSIS
A. Initial diagnostic evaluation.
1. Goal is to differentiate between benign and potentially life-threatening causes.
2. Presence of cardiovascular disease identifies patients at increased risk of sudden death.
