• Transient loss of consciousness characterized by unresponsiveness, loss of postural tone, and spontaneous recovery usually caused by cerebral hypoxemia
• System(s) affected: Cardiovascular; Nervous

Incidence

• Up to 20% of adults will have ≥1 episode by age 75; 15% of children <18 years of age
• Accounts for 1–6% of hospital admissions and ~3% of emergency room visits

Prevalence In institutionalized elderly (>75 years), 6%

• Heart disease
• Dehydration
• Drugs:
  • Antihypertensives
  • Vasodilators (including calcium channel blockers, ACE inhibitors, and nitrates)
  • Phenothiazines
  • Antidepressants
  • Antiarrhythmics
  • Diuretics

Genetics Specific cardiomyopathies and arrhythmias may be familial (i.e., long QT syndrome, hypertrophic cardiomyopathy).

See “Risk Factors.”

• In some cases, vagal response leads to decreased heart rate.
• Systemic hypotension secondary to decreased cardiac output and/or systemic vasodilation leads to a drop in cerebral perfusion and resulting loss of consciousness.

• Cardiac: Obstruction to outflow:
  • Aortic stenosis
  • Hypertrophic cardiomyopathy
  • Pulmonary embolus
  • Anomalous coronary artery origin resulting in cardiac ischemia
• Cardiac arrhythmias:
  • Sustained ventricular tachycardia (VT)
  • Supraventricular tachycardia (atrial fibrillation, atrial flutter, re-entrant SVT)
  • Second- and third-degree AV block
  • Sick-sinus syndrome
  • Pacing-induced infranodal block
  • H-V interval >100 ms
• Noncardiac:
  • Reflex-mediated vasovagal (neurocardiogenic/neurally mediated), situational (micturition, defecation, cough)
  • Orthostatic hypotension
  • Drug-induced
  • Neurologic: Seizures; transient ischemic attack (can in theory cause syncope, but presentation usually markedly clinically different from pure syncope)
  • Carotid sinus hypersensitivity
  • Psychogenic

See “Etiology.”

• Careful history, physical exam, and an ECG are more important than other investigations in determining the diagnosis (1)[A]. Syncope associated with physical exertion suggests a potential cardiac etiology.
• Make sure that the patient or witness (if present) is not talking about vertigo (i.e., sense of rotary motion, spinning, and whirling), seizure, or causes of fall without loss of consciousness.
• Even after careful evaluation, including diagnostic procedures and special tests, the cause will be found in only 50–60% of the patients.
• Onset of syncope is usually rapid, and recovery is spontaneous, rapid, and complete. Duration of episodes are typically brief (<60 seconds). The presence of underlying cardiac or neurologic conditions provides the key to diagnosis.

• BP and pulse, both lying and standing
• Check for cardiac murmur or focal neurologic abnormality.

History and physical examination should guide laboratory testing.

LabInitial Labs Consider (not all indicated in all individuals):

• CBC
• Electrolytes, BUN, creatinine, glucose (rarely helpful: <2% have hyponatremia, hypocalcemia, hypoglycemia, or renal failure causing seizures).
• Cardiac enzymes
• D-dimer (for pulmonary embolism workup)
• HCG

Follow-Up and Special Considerations

• If history and physical suggest ischemic, valvular, or congenital heart disease:
  • ECG
  • Exercise stress test (if syncope with exertion)
  • Echocardiogram
  • Cardiac catheterization
• If CNS disease suspected:
  • EEG
  • Head CT scan
  • Head MRI/MRA when vascular cause is suspected
  • Do not order these tests unless there are hints of CNS disease on history or physical exam.
• ECG monitoring, either in hospital or ambulatory (Holter):
  • Useful in 4–15% of patients
  • Should be done in patients with heart disease or recurrent syncope
  • Arrhythmias frequently documented, but not always associated with syncope
• Electrophysiologic studies:
  • Have been positive in 18–75% of patients
  • Induction of VT and dysfunction of His-Purkinje system are the 2 most common abnormalities.
  • Should be done in patients with heart disease or recurrent syncope, although they may not show whether arrhythmia noted or induced during study is cause of syncope
• Carotid hypersensitivity evaluation:
  • Carotid hypersensitivity should be considered in patients with syncope during head turning, especially while wearing tight collars, and with neck tumors and neck scars.
  • The technique is not standardized; 1 side at a time is compressed gently at a time for 20 seconds with constant monitoring of pulse and BP/ECG.
  • Atropine should be readily available.
• Tilt-table testing ± isoproterenol infusion:
  • Provocative test for vasovagal syncope
  • Perform if cardiac causes have been excluded; role in workup of patients with syncope of unknown origin
  • Not standardized but has been reported positive (symptomatic hypotension and bradycardia) in 26–87% of patients; also positive in up to 45% of control subjects
• Psychiatric evaluation: Anxiety, depression, and alcohol and drug abuse can be associated with syncope.

Imaging

• ECG
• Echocardiogram if clinically indicated

Initial Imaging Approach Lung scan or helical CT scan of thorax if history and physical exam suggest pulmonary embolism (PE)

Diagnostic Procedures/Other Patient-activated implantable loop recorders can record 4–5 minutes of retrograde ECG rhythm. Helpful in recurrent syncope, with yield of 24–47%.

Pathological Findings Depends on etiology and presence of underlying cardiac or neurologic conditions

• Drop attacks
• Coma
• Vertigo
• Seizure disorder

Maintaining good hydration status and normal salt intake are initial therapy. Educate patients of the premonitory signs of syncope.

First Line

• Geared toward specific underlying cardiac or neurologic abnormalities
• In cases of recurrent vasovagal/neurocardiogenic/neurally mediated syncope:
  • β-Adrenergic blockers
  • Mineralocorticoids (fludrocortisone)
  • α-Adrenergic agonists (midodrine)

Second Line

• SSRIs (paroxetine, sertraline, fluoxetine)
• Vagolytics (disopyramide)

General Measures

• Patients with heart disease should be admitted to the hospital for evaluation.
• Elderly patients without previously recognized heart disease should be admitted if the physician thinks that the cause of syncope is likely cardiac.
• Patients without heart disease, especially young patients (<60 years old), can be worked up safely as outpatients.
• Prescribe antiarrhythmics for documented arrhythmias occurring simultaneously with syncope or symptoms of presyncope. Asymptomatic arrhythmias do not necessarily require treatment.
• The decision to treat patients on basis of arrhythmias or conduction abnormalities provoked or detected during EPS is even more problematic: Does the arrhythmia or conduction abnormality have anything to do with the patient’s symptoms?
• Most would treat patients with provoked sustained VT with an antiarrhythmic drug that suppressed arrhythmia during study.
• Rationale for such treatment: Recurrent syncope is less frequent in patients with positive EPS who are treated than it is in those who have negative EPS.

Issue for Referral When cardiac or neurologic etiologies are suspected, appropriate expert consultation is indicated.

St. John's wort has been used in cases of recurrent noncardiac syncope.

• ICD placement for patients with cardiac conditions with high risk of sudden death and/or recurrent syncope on medications (i.e., long QT syndrome, hypertrophic cardiomyopathy)
• Many recommend pacemaker implantation in patients with
  • Second- (Mobitz type II) and third-degree heart block
  • H-V intervals >100 ms
  • Pacing-induced infranodal block
  • Sinus node recovery time ≥3 seconds

Initial Stabilization

• Support ABCs.
• Stabilize heart rate and BP, typically with IV fluids.

Admission Criteria Patients with heart disease should be admitted to the hospital for evaluation.

IV Fluids Use isotonic crystalloid fluids for fluid resuscitation if needed.

Nursing Close monitoring of BP, heart rate during initial presentation

Discharge Criteria

• Attainment of hemodynamic stability
• Satisfactory completion of workup for etiology
• Adequate control of specific arrhythmia or seizure, if present

Patient Monitoring

• Frequent follow-up visits for patients with cardiac causes of syncope, especially patients on antiarrhythmics
• Patients with an unknown cause of syncope rarely (5%) are diagnosed during the follow-up.

• No specific diet unless the patient has heart disease
• Increased fluid and salt intake to maintain intravascular volume in cases of recurrent vasovagal syncope

• Reassure the patient that most cardiac causes of syncope can be treated, and patients with noncardiac causes do well, even if the cause of syncope is never discovered.
• The physician and patient should carefully consider whether the patient should continue to drive while syncope is being evaluated. Physicians should be aware of pertinent laws in their own states.

• Cumulative mortality at 2 years:
  • Low (25%): Young patients (<60 years) with noncardiac or unknown cause of syncope
  • Intermediate (20%): Older patients (>60 years) with noncardiac or unknown cause of syncope
  • High (32–38%): Patients with cardiac cause of syncope
• Independent predictors of poor short-term outcomes:
  • Abnormal ECG
  • Shortness of breath
  • Systolic BP <90 mm Hg
  • Hematocrit <30%
  • Congestive heart failure

• Trauma from falling
• Death (see “Prognosis”)

• European Heart Rhythm Association (EHRA); Heart Failure Association (HFA) et al. Guidelines for the diagnosis and management of syncope (version 2009): The Task Force for the Diagnosis and Management of Syncope of the European Society of Cardiology (ESC). Eur Heart J. 2009;30(21):2631–71.
• Goble MM, Benitez C, Baumgardner M, et al. ED management of pediatric syncope: Searching for a rationale. Am J Emerg Med. 2008;26:66–70.
• Kuriachan V, Sheldon RS, Platonov M. Evidence-based treatment for vasovagal syncope. Heart Rhythm. 2008;5:1609–14.
• Parry SW, Tan MP. An approach to the evaluation and management of syncope in adults. BMJ. 2010;340:c880.
• Reed MJ, Newby DE, Coull AJ, et al. The ROSE (risk stratification of syncope in the emergency department) study. J Am Coll Cardiol. 2010;55:713–21.
• Romme JJ, Reitsma JB, Go-Schön IK, et al. Prospective evaluation of non-pharmacological treatment in vasovagal syncope. Europace. 2010;12:567–73.
• Strickberger SA, Benson DW, Biaggioni I. AHA/ACCF scientific statement on the evaluation of syncope: From the American Heart Association Councils on Clinical Cardiology, Cardiovascular Nursing, Cardiovascular Disease in the Young, and Stroke, and the Quality of Care and Outcomes Research Interdisciplinary Working Group; and the American College of Cardiology Foundation in Collaboration with the Heart Rhythm Society. J Am Coll Cardiol. 2006;47:473–84.

• Aortic Valvular Stenosis; Atrial Septal Defect (ASD); Carotid Sinus Hypersensitivity; Idiopathic Hypertrophic Subaortic Stenosis (IHSS); Patent Ductus Arteriosus; Pulmonary Arterial Hypertension; Pulmonary Embolism; Seizure Disorders; Stokes-Adams Attacks
• Algorithms: Syncope; Transient Ischemic Attack and Transient Neurologic Deficit

780.2 Syncope and collapse

R55 Syncope and collapse

271594007 syncope (disorder)

• A careful history and physical are key to a diagnosis.
• Use the ECG/event-recorder to evaluate for cardiac conditions.
• True neurologic causes of syncope are very rare; cardiac causes by far are more common.
• Fewer than 2% of cases are caused by hyponatremia, hypocalcemia, hypoglycemia, or renal failure causing seizures.

Santiago O. Valdes, MD
Ricardo A. Samson, MD

1. Kessler C, Tristano JM, De Lorenzo R. The emergency department approach to syncope: Evidence-based guidelines and prediction rules. Emerg Med Clin North Am. 2010;28:487–500.  [PMID:20709240]

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