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Syncope is a neurobehavioral manifestation that is a "transient loss of consciousness and postural tone caused by diminished blood flow to the brain (i.e., brain ischemia). Presyncope refers to the sensation of lightheadedness and loss of strength that precedes a syncopal event or accompanies an incomplete syncope."[1]


A meta-analysis has summarized the most common causes:[2]

  • No diagnosis was made in one third of patients
  • "The most frequent diagnosis was 'situational, orthostatic or vasavagal syncope'" 29%
  • Bradyarrhythmia, 5%
  • Tachyarrhythmia 3%

About 25% of patients have a cardiac cause, 15% are vasovagal and 10% are due to orthostatic hypotension.[3][4] About 3% are from myocardial infarction, 91% having normal ST-segments.[5] In octogenarians, 10% are from arrhythmias.[6]

2% have a cerebrovascular cause.[3] Generally, this is consider when there is basilar artery or bilateral vertebral or bilateral carotid stenoses severe stenoses. However, there are case reports suggesting unilateral carotid stenoses can cause syncope.[7] However, it is not clear if these patients also had focal neurological symptoms.

2% are due to seizures.[3]

Vasovagal syncope (also called neurocardiogenic syncope, neurogenic syncope, or vasodepressor syncope is the cause of syncope in about 15% of patients.[3] Vasovagal syncope is "loss of consciousness due to a reduction in blood pressure that is associated with an increase in vagal tone and peripheral vasodilation".[8] Vasovagal syncope includes vasodepressor syncope which is syncope during fright or stress. Sometimes asystole occurs and a pacemaker is needed.[9]

Some authors use neurocardiogenic syncope or neurally mediated syncope as the broad term, and within this category are the parasympathetic mediated syncopes: 1) vasovagal syncope (syncope during fright or stress), 2) situational syncope (syncope following cough, micturition, or defecation), and 3) carotid sinus syncope (also called carotid sinus hypersensitivity).[10]


Clinical practice guidelines are available to guide diagnosis.[11][12]

History and physical

An evaluation based on the initial history and physical examination will correctly diagnose the underlying cause in 63% of patients according to one case series.[13] Interviewing witnesses must be carefully done.[14] Allowing observers to answer "I do not know" may be important.[14]

"Palpitations before syncope, syncope during effort or in supine position, absence of autonomic prodromes and absence of predisposing and/or precipitating factors were found to be predictors of cardiac syncope."[15]

Two or more prodromal symptoms suggests suggests vasovagal syncope or a psychiatric disorder.[16]

Having no warning symptoms suggests a cardiac arrhythmia.[17] Having more than one prodrome symptom (e.g. dizzines, nausea) is predictive of vasovagal and psychogenic syncope.[16]

The Calgary Syncope Symptom Score is a clinical prediction rule whose accuracy in an independent validation was:[18]

Physical examination

Measurement of the postural blood pressure is very important for diagnosis and management.[19] Details of interpreting this test have been published by the Rational Clinical Examination.[20]

Testing or carotid sinus hypersensitivity may be best done with the patients standing.[21]


"Abnormal ECG and/or heart disease... found to be predictors of cardiac syncope."[15]

A p-wave longer than 120 ms on electrocardiogram is suggestive of a cardiac arrhythmia.[16]

Evaluation of the vertebral and carotid arteries with transcranial and carotid dopplers is mainly helpful if there are focal neurological findings.[22][23]

A clinical practice guideline by the American College of Physicians recommends "neurologic testing, including electroencephalography, computed tomography, and carotid and transcranial Doppler ultrasonography, should be reserved for patients who have neurologic signs or symptoms or carotid bruits".[24]

Clinical prediction rule

A clinical prediction rule is available to help identify patients with cardiac causes of syncope.[15]


Prognosis of syncope
Cause of syncope 1 year[3] 5 years[4]
mortality sudden death mortality sudden death
All cases 14%   34% 14%
Cardiac cause 30% 24% 50% 33%
Noncardiac 12% 4% 30% 5%
Unknown 6% 3% 24% 9%

The San Francisco Syncope Rule (online) can predict the chance of serious events within seven days. A meta-analysis found:[25]

  • Sensitivity 87% (most likely to miss cardiac arrhythmias)
  • Specificity 52%
  • Substantial between-study heterogeneity
  • Regarding missed diagnoses, "the probability was 2% or lower when the rule was applied only to patients for whom no cause of syncope was identified after initial evaluation in the emergency department."[25]

The ROSE (Risk Stratification of Syncope in the Emergency Department) prediction rule contains:[26]

For patients who have syncope while driving, recurrence rates are:[27]

  • 20% rate during any activity. About 50% occurred within the first 6 months.
  • 7% rate during driving. About 70% occurred more than one year after the initial event

Alternative scores, including the Boston criteria 21421292, are available.[28]


  1. Anonymous (2023), Syncope (English). Medical Subject Headings. U.S. National Library of Medicine.
  2. D'Ascenzo F, Biondi-Zoccai G, Reed MJ, Gabayan GZ, Suzuki M, Costantino G et al. (2011). "Incidence, etiology and predictors of adverse outcomes in 43,315 patients presenting to the Emergency Department with syncope: An international meta-analysis.". Int J Cardiol. DOI:10.1016/j.ijcard.2011.11.083. PMID 22192287. Research Blogging.
  3. 3.0 3.1 3.2 3.3 3.4 Kapoor WN, Karpf M, Wieand S, Peterson JR, Levey GS (July 1983). "A prospective evaluation and follow-up of patients with syncope". N. Engl. J. Med. 309 (4): 197–204. PMID 6866032[e]
  4. 4.0 4.1 Kapoor WN (May 1990). "Evaluation and outcome of patients with syncope". Medicine (Baltimore) 69 (3): 160–75. PMID 2189056[e] [Full text from OVID]
  5. McDermott D, Quinn JV, Murphy CE (March 2009). "Acute myocardial infarction in patients with syncope". CJEM 11 (2): 156–60. PMID 19272217[e]
  6. Kühne M, Schaer B, Sticherling C, Osswald S (2011). "Holter monitoring in syncope: diagnostic yield in octogenarians.". J Am Geriatr Soc 59 (7): 1293-8. DOI:10.1111/j.1532-5415.2011.03486.x. PMID 21718271. Research Blogging.
  7. Kashiwazaki D, Kuroda S, Terasaka S, et al (January 2005). "[Carotid occlusive disease presenting with loss of consciousness]" (in Japanese). No Shinkei Geka 33 (1): 29–34. PMID 15678866[e]
  8. Anonymous (2023), Vasovagal syncope (English). Medical Subject Headings. U.S. National Library of Medicine.
  9. Brignole M, Menozzi C, Moya A, Andresen D, Blanc JJ, Krahn AD et al. (2012). "Pacemaker Therapy in Patients With Neurally Mediated Syncope and Documented Asystole: Third International Study on Syncope of Uncertain Etiology (ISSUE-3): A Randomized Trial.". Circulation 125 (21): 2566-2571. DOI:10.1161/CIRCULATIONAHA.111.082313. PMID 22565936. Research Blogging.
  10. Mathias CJ, Deguchi K, Schatz I (February 2001). "Observations on recurrent syncope and presyncope in 641 patients". Lancet 357 (9253): 348–53. DOI:10.1016/S0140-6736(00)03642-4. PMID 11210997. Research Blogging.
  11. Cooper PN, Westby M, Pitcher DW, Bullock I (2011). "Synopsis of the National Institute for Health and Clinical Excellence Guideline for management of transient loss of consciousness.". Ann Intern Med 155 (8): 543-9. DOI:10.1059/0003-4819-155-8-201110180-00368. PMID 21930835. Research Blogging.
  12. Brignole M, Alboni P, Benditt DG, et al (November 2004). "Guidelines on management (diagnosis and treatment) of syncope-update 2004. Executive Summary". Eur. Heart J. 25 (22): 2054–72. DOI:10.1016/j.ehj.2004.09.004. PMID 15541843. Research Blogging.
  13. van Dijk N, Boer KR, Colman N, et al (2008). "High diagnostic yield and accuracy of history, physical examination, and ECG in patients with transient loss of consciousness in FAST: the Fainting Assessment study". J. Cardiovasc. Electrophysiol. 19 (1): 48–55. DOI:10.1111/j.1540-8167.2007.00984.x. PMID 17916139. Research Blogging.
  14. 14.0 14.1 Thijs RD, Wagenaar WA, Middelkoop HA, Wieling W, van Dijk JG (November 2008). "Transient loss of consciousness through the eyes of a witness". Neurology 71 (21): 1713–8. DOI:10.1212/01.wnl.0000335165.68893.b0. PMID 19015487. Research Blogging.
  15. 15.0 15.1 15.2 Del Rosso A, Ungar A, Maggi R, Giada F, Petix NR, De Santo T et al. (2008). "Clinical predictors of cardiac syncope at initial evaluation in patients referred urgently to a general hospital: the EGSYS score.". Heart 94 (12): 1620-6. DOI:10.1136/hrt.2008.143123. PMID 18519550. Research Blogging. Review in: Evid Based Med. 2009 Jun;14(3):91 Cite error: Invalid <ref> tag; name "pmid18519550" defined multiple times with different content Cite error: Invalid <ref> tag; name "pmid18519550" defined multiple times with different content
  16. 16.0 16.1 16.2 Graf D, Schlaepfer J, Gollut E, van Melle G, Mischler C, Fromer M et al. (2008). "Predictive models of syncope causes in an outpatient clinic.". Int J Cardiol 123 (3): 249-56. DOI:10.1016/j.ijcard.2006.12.007. PMID 17397948. Research Blogging. Cite error: Invalid <ref> tag; name "pmid17397948" defined multiple times with different content Cite error: Invalid <ref> tag; name "pmid17397948" defined multiple times with different content
  17. Krahn AD, Klein GJ, Yee R, Skanes AC (May 2001). "Predictive value of presyncope in patients monitored for assessment of syncope". Am. Heart J. 141 (5): 817–21. DOI:10.1067/mhj.2001.114196. PMID 11320372. Research Blogging.
  18. Gravel J, Hedrei P, Grimard G, Gouin S (2009). "Prospective validation and head-to-head comparison of 3 ankle rules in a pediatric population.". Ann Emerg Med 54 (4): 534-540.e1. DOI:10.1016/j.annemergmed.2009.06.507. PMID 19647341. Research Blogging.
  19. Mendu ML, McAvay G, Lampert R, Stoehr J, Tinetti ME (2009). "Yield of diagnostic tests in evaluating syncopal episodes in older patients.". Arch Intern Med 169 (14): 1299-305. DOI:10.1001/archinternmed.2009.204. PMID 19636031. Research Blogging.
  20. McGee S, Abernethy WB, Simel DL (1999). "The rational clinical examination. Is this patient hypovolemic?". JAMA 281 (11): 1022-9. DOI:10.1001/jama.281.11.1022. PMID 10086438. Research Blogging. “A large postural pulse change (> or =30 beats/min) or severe postural dizziness is required to clinically diagnose hypovolemia due to blood loss, although these findings are often absent after moderate amounts of blood loss. In patients with vomiting, diarrhea, or decreased oral intake, few findings have proven utility, and clinicians should measure serum electrolytes, serum blood urea nitrogen, and creatinine levels when diagnostic certainty is required.”
  21. Parry SW, Richardson DA, O'Shea D, Sen B, Kenny RA (2000). "Diagnosis of carotid sinus hypersensitivity in older adults: carotid sinus massage in the upright position is essential". Heart 83 (1): 22–3. PMID 10618329[e]
  22. Schnipper JL, Ackerman RH, Krier JB, Honour M (April 2005). "Diagnostic yield and utility of neurovascular ultrasonography in the evaluation of patients with syncope". Mayo Clin. Proc. 80 (4): 480–8. PMID 15819284[e]
  23. Pires LA, Ganji JR, Jarandila R, Steele R (2001). "Diagnostic patterns and temporal trends in the evaluation of adult patients hospitalized with syncope". Arch. Intern. Med. 161 (15): 1889–95. PMID 11493131[e]
  24. Linzer M, Yang EH, Estes NA, Wang P, Vorperian VR, Kapoor WN (June 1997). "Diagnosing syncope. Part 1: Value of history, physical examination, and electrocardiography. Clinical Efficacy Assessment Project of the American College of Physicians". Ann. Intern. Med. 126 (12): 989–96. PMID 9182479[e]
  25. 25.0 25.1 Saccilotto RT, Nickel CH, Bucher HC, Steyerberg EW, Bingisser R, Koller MT (2011). "San Francisco Syncope Rule to predict short-term serious outcomes: a systematic review.". CMAJ 183 (15): E1116-26. DOI:10.1503/cmaj.101326. PMID 21948723. PMC PMC3193123. Research Blogging.
  26. Reed MJ, Newby DE, Coull AJ, Prescott RJ, Jacques KG, Gray AJ (2010). "The ROSE (risk stratification of syncope in the emergency department) study.". J Am Coll Cardiol 55 (8): 713-21. DOI:10.1016/j.jacc.2009.09.049. PMID 20170806. Research Blogging.
  27. Sorajja D, Nesbitt GC, Hodge DO, Low PA, Hammill SC, Gersh BJ et al. (2009). "Syncope while driving: clinical characteristics, causes, and prognosis.". Circulation 120 (11): 928-34. DOI:10.1161/CIRCULATIONAHA.108.827626. PMID 19720940. Research Blogging.
  28. Sun BC, Derose SF, Liang LJ, Gabayan GZ, Hoffman JR, Moore AA et al. (2009). "Predictors of 30-day serious events in older patients with syncope.". Ann Emerg Med 54 (6): 769-778.e1-5. DOI:10.1016/j.annemergmed.2009.07.027. PMID 19766355. PMC PMC2788122. Research Blogging.

See also