Syncope

Syncope is defined as a transient, self-limited loss of consciousness with an inability to maintain postural tone that is followed by spontaneous recovery. This definition excludes seizures, coma, shock, or other states of altered consciousness. Although most causes of syncope are benign, this symptom presages a life-threatening event in a small subset of patients.

Essential update: Predicting serious outcome and death in patients with syncope
Peak troponin concentration is associated with an increased risk of serious outcome and death in patients with syncope, and this risk increases with higher concentrations, according to a prospective cohort study of 338 patients who had plasma troponin levels measured 12 hours after syncope with the ARCHITECT STAT sensitive troponin I assay.[1] The percentage of patients with a serious outcome increased across patients divided into quintiles on the basis of peak troponin concentration at 1 month (0%, 9%, 13%, 26%, 70%) and at 1 year (10%, 22%, 26%, 52%, 85%).[1]

Signs and symptoms
History and physical examination are the most specific and sensitive ways of evaluating syncope. These measures, along with 12-lead electrocardiography (ECG), are the only current level A recommendations listed in the 2007 American College of Emergency Physicians (ACEP) Clinical Policy on Syncope.[2]

A detailed account of the event must be obtained from the patient, including the following:

Precipitant factors
Activity the patient was involved in before the event
Position the patient was in when the event occurred
The following questions should be asked:

Was loss of consciousness complete?
Was loss of consciousness with rapid onset and short duration?
Was recovery spontaneous, complete, and without sequelae?
Was postural tone lost?
If the answers are positive, syncope is highly likely; if 1 or more are negative, other forms of loss of consciousness should be considered.[3]

Presyncopal symptoms reported may include the following:

Prior faintness, dizziness, or light-headedness (70% of cases of true syncope)
Prior vertigo, weakness, diaphoresis, epigastric discomfort, nausea, blurred or faded vision, pallor, or paresthesias
Red flag symptoms: Exertional onset, chest pain, dyspnea, low back pain, palpitations, severe headache, focal neurologic deficits, diplopia, ataxia, or dysarthria
Other information that should be obtained includes the following:

Detailed account of the event from any available witnesses (eg, whether patient experienced postevent confusion)
Patient’s medication history
Patient’s personal or familial medical history of cardiac disease
A complete physical examination is required, with particular attention to the following:

Analysis of vital signs
Measurement of the glucose level by rapid fingerstick
Detailed cardiopulmonary examination
Detailed neurologic examination
Assessment for signs of trauma
Stool guaiac examination
Bedside examinations to help elucidate the origin of syncope (eg, Hallpike maneuver)
See Clinical Presentation for more detail.

Diagnosis
No specific laboratory testing has sufficient power to be absolutely indicated for evaluation of syncope. Research-based and consensus guideline recommendations are as follows:

Serum glucose
Complete blood count
Serum electrolytes
Cardiac enzymes
Total creatine kinase
Urinalysis/dipstick
Imaging studies that may be helpful include the following:

Chest radiography: May serve to identify pneumonia, congestive heart failure (CHF), lung mass, effusion, or widened mediastinum
Computed tomography (CT) of the head (noncontrast): Has a low diagnostic yield in syncope but may be clinically indicated in patients with new neurologic deficits or in patients with head trauma secondary to syncope
CT of the chest and abdomen: Indicated only in select cases (eg, suspected aortic dissection, ruptured abdominal aortic aneurysm, or pulmonary embolism [PE])
Magnetic resonance imaging (MRI) of the brain and magnetic resonance arteriography (MRA): May be required in select cases to evaluate vertebrobasilar vasculature
Ventilation-perfusion (V/Q) scanning: Appropriate for suspected PE
Echocardiography: The test of choice for evaluating suspected mechanical cardiac causes of syncope
A standard 12-lead ECG is a level A recommendation in the 2007 ACEP consensus guidelines for syncope.[2] The following considerations are relevant:

Normal ECG findings are a good prognostic sign
ECG can be diagnostic for acute myocardial infarction or myocardial ischemia and can provide objective evidence of preexisting cardiac disease or dysrhythmia
Bradycardia, sinus pauses, nonsustained ventricular tachycardia and sustained ventricular tachycardia, and atrioventricular conduction defects are truly diagnostic only when they coincide with symptoms
Loop recorders have a higher diagnostic yield than Holter monitor evaluation, with a marginal cost savings[4]
Ambulatory monitoring appears to have a higher negative than positive diagnostic yield[5]
Other diagnostic tests and procedures include the following:

Head-up tilt-table test: Useful for confirming autonomic dysfunction and can generally be safely arranged on an outpatient basis
Electroencephalography (EEG): Can be performed at the discretion of a neurologist if seizure is considered a likely alternative diagnosis
Stress test: A cardiac stress test is appropriate for patients in whom cardiac syncope is suspected and who have risk factors for coronary atherosclerosis
Carotid sinus massage (to diagnose carotid sinus syncope)
See Workup for more detail.

Management
Prehospital management of syncope may require the following:

Intravenous access
Oxygen administration
Advanced airway techniques
Glucose administration
Pharmacologic circulatory support
Pharmacologic or mechanical restraints
Defibrillation or temporary pacing
Advanced triage decisions, such as direct transport to multispecialty tertiary care centers, may be required in select cases.

In patients brought to the emergency department with a presumptive diagnosis of syncope, appropriate initial interventions include the following:

IV access, oxygen administration, and cardiac monitoring
ECG and rapid blood glucose evaluation
The treatment choice for syncope depends on the cause or precipitant of the syncope, as follows:

Situational syncope: Patient education regarding the condition

Orthostatic syncope: Patient education; additional therapy in the form of thromboembolic disease (TED) stockings, mineralocorticoids, and other drugs (eg, midodrine); elimination of drugs associated with hypotension; intentional oral fluid consumption
Cardiac arrhythmic syncope: Antiarrhythmic drugs or pacemaker placement
Cardiac mechanical syncope: Beta blockade; if valvular disease is present, surgical correction
See Treatment and Medication for more detail