Syncope overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sahar Memar Montazerin, M.D.[2]
Overview
Syncope (IPA: Template:IPA and Template:IPA), is a sudden, and generally momentary, loss of consciousness, or blacking out caused by the Central Ischaemic Response, because of a lack of sufficient blood and oxygen in the brain. The first symptoms a person feels before fainting are dizziness; a dimming of vision, or brownout; tinnitus; and feeling hot. Moments later, the person's vision turns black, and he or she drops to the floor (or slumps if seated in a chair). If the person is unable to slump from the position to a near-horizontal position, he or she risks dying of the Suspension trauma effect. More serious causes of fainting include cardiac (heart-related) causes such as an abnormal heart rhythm (an arrhythmia), where the heart beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain. Some arrhythmias can be life-threatening. Other important cardio-vascular conditions that can be manifested by syncope include subclavian steal syndrome and aortic stenosis.
Historical Perspective
There is limited information about the historical perspective of syncope.
Classification
Syncope is usually classified based on the underlying mechanisms leading to hypoperfusion. According to European Society of Cardiology (ESC) guideline, syncope is classified to neurally-mediated, orthostatic hypotension, and cardiovascular subtypes. There are some conditions that are incorrectly diagnosed as syncope. These conditions are usually associated with partial or complete loss of consciousness such as epilepsy, metabolic disorders, transient ischemic attack or conditions with loss of posture and without loss of consciousness like cataplexy, drop attacks, falls and pseudo-syncope.
Pathophysiology
Syncope is an entity in which loss of conscience due to cerebral hypoperfusion presents. There are several pathways to explain its pathophysiology, depending on if it is either reflex syncope, orthostatic intolerance, or cardiovascular syncope.
Causes
Peripheral vascular resistance and cardiac output are the two main determinants for the presentation of syncope. autonomic nervous system impairment due to drugs or an autonomic failure, can lead to a decrease in peripheral vascular resistance. Reflex activity impairment may also cause a decrease of peripheral vascular resistance, as the body normal compensation reflexes fail. Decrease in cardiac output may be due to venous pooling, cardioinhibitory reflexes, arrhythmia, hypertension, pulmonary embolism, and volume depletion leading to diminished venous return, among others.
Differentiating Syncope from other Diseases
Syncope should be differentiated from other conditions causing partial or complete loss of consciousness. These disorders may include, coma, dizziness, seizure, and vertigo. There are conditions that may mistakenly be diagnosed as syncope. These conditions include epilepsy, hypoglycemia, intoxication, cataplexy, and transient ischemic attacks.
Epidemiology and Demographics
The incidence of syncope ranges from 260 to 1950 cases per 100,000 individuals worldwide. It increases with age and especially after age 70 years old. Syncope affects men and women equally.
Risk Factors
Syncope is a sign of insufficient cerebral blood flow and it should be evaluated for the underlying cause. Possible underlying causes of syncope include structural heart disease, vasovagal syncope and arrhythmia. Risk factors associated with the development of either of these disorders may contribute to the development of syncope.
Natural History, Complications, and Prognosis
Patients with syncope are at risk of the development of complications, such as trauma from frequent falls and Sudden cardiac death. The prognosis of syncope depends on underlying causes. Syncope caused by cardiovascular diseases may be life-threatening and is an important cause of sudden cardiac death. Prognosis of vasovagal syncope is favorable.
Diagnosis
History and Symptoms
Syncope itself is a symptom. Patients with syncope may feel balcking out, dizziness, lightheadedness, and temporary loss of consciousness. Patients may experience other symptoms based on the underlying causes of the syncope.
Physical Examination
Patients with syncope usually appear normal. Physical examination of patients with syncope is usually remarkable for cardiac murmur, orthostatic hypotension, and altered level of consciousness.
Laboratory Findings
There are no diagnostic laboratory findings associated with syncope. Some patients with syncope may have acidosis, which is usually suggestive of insufficient blood flow. Other possible laboratory findings may include hypoglycemia, increased lactate level, hypoxia, and hypercapnia.
Electrocardiogram
Generally, the ECG of individuals with syncope is normal. However, ECG may be remarkable for an arrhythmia. The arrhythmia may be seen on the EKG include sinus bradycardia <40 beats/min or repetitive sinoatrial blocks or sinus pauses > 3s, Mobitz II 2nd or 3rd-degree atrioventricular block, alternating left and right bundle branch block, rapid paroxysmal supraventricular tachycardia, ventricular tachycardia, and pacemaker malfunction with cardiac pauses.
X-ray
There are no x-ray findings associated with syncope.
CT
There are no CT scan findings associated with syncope.
MRI
There are no MRI findings associated with syncope.
Echocardiography
Transthoracic echocardiography can be useful in the diagnostic workup of patients presenting with syncope. This evaluation is especially warranted in patients who are suspected to have underlying cardiovascular disorders.
Other Diagnostic Studies
A tilt table test can help to reveal abnormal cardiovascular reflexes that produce syncope. During the test, you stand and your initial blood pressure and heart rate are recorded as the baseline. Then the table is tilted at 70 degrees for 45 minutes. Your blood pressure and heart rate are recorded again. At the same time, the nurse observes whether symptoms such as nausea or vomiting appear. A positive result suggests the possibility of vasovagal syncope.
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Surgical intervention is not recommended for the management of syncope.
Primary Prevention
There are no established measures for the primary prevention of syncope.
Secondary Prevention
There are no established measures for the secondary prevention of syncope.