Syncope and Other Causes of Transient Loss of Consciousness

Chapter: Syncope and Other Causes of Transient Loss of Consciousness
McMaster Section Editor(s): Akbar A. Panju
Section Editor(s) in Interna Szczeklika: Miłosz Jankowski
McMaster Author(s): Serena Gundy, Jason Cheung, Mohamed Panju, Ameen Patel
Author(s) in Interna Szczeklika: Piotr Kułakowski
Additional Information

Syncope is a transient loss of consciousness caused by cerebral hypoperfusion. It is characterized as a loss of postural tone of a rapid onset, short duration, and with spontaneous recovery without neurological deficits. Syncope can be classified into several broad categories (Table. Syncope: Causes and management suggestions...).

In presyncope (a syncopal prodrome), the patient has a sensation of imminent loss of consciousness, but true syncope does not occur.

Other causes of symptoms that can mimic syncope include sudden-onset conditions not associated with loss of consciousness, such as a fall or psychogenic pseudosyncope [appearance of transient loss of consciousness in the absence of true loss of consciousness]), or conditions associated with partial or complete loss of consciousness not primarily related to cerebral hypoperfusion (metabolic disturbances [eg, hypoglycemia], hypoxia, hyperventilation with hypocapnia), seizure, drug or alcohol intoxication).

General Approach to SyncopeTop

1. During loss of consciousness, manage patients as outlined in the chapter on loss of consciousness.

2. Exclude other causes of transient loss of consciousness.

3. Identify clinical features suggestive of a cardiac etiology.

4. Stratify patients into low-risk and high-risk (requiring prompt diagnostic testing).

5. Provide a provisional diagnosis and management plan.

6. Identify when driving privileges should be held (follow local laws and regulations).

Initial Evaluation of a Syncopal Patient

1. Detailed and comprehensive history:

1) Context at the onset of symptoms: After standing, with dehydration, with administration of medications or drugs (suggestive of orthostatic cause), related to exposures (vasovagal), on exertion, with head turning (carotid artery occlusion), or when supine.

2) Prodromal symptoms: Weakness, presyncope, visual blurring, diaphoresis, nausea, terminal warmth (vasovagal), or lack of prodromal symptoms (cardiac).

3) Symptoms following the event: Rapid return of consciousness (cardiac) vs confusion, focal weakness, or delayed return to baseline (seizure).

4) Collateral history of the event: Appearance during the event, including the overall duration, presence of seizure symptoms, signs of pseudosyncope (slumping to the floor, lack of trauma, closed eyes, lack of diaphoresis).

2. Physical examination:

1) Vitals including the orthostatic blood pressure and heart rate.

2) Neurologic examination: A screening examination for focal deficits.

3) Cardiovascular examination: Jugular veins, enlarged/displaced apical beat, murmurs, bruits, signs of congestive heart failure.

3. Investigations:

1) A 12-lead electrocardiography (ECG) is performed to look for signs of conduction disturbances, ischemia, preexcitation syndromes (long QT, delta wave, or Brugada syndrome [right bundle branch block with ST-segment elevation in leads V1-V3]).

2) Echocardiogram is performed in all patients with signs of possible structural heart disease including aortic stenosis, hypertrophic cardiomyopathy, pulmonary embolism, pulmonary hypertension, and ischemia.

3) Other investigations are utilized to identify the etiology of the syncopal event as dictated by the history, physical examination, and ECG.

Identification of Risk for Serious Outcomes After the Event Top

Patients with syncope who present to medical attention may have a significant risk during the follow-up; however, the gravity of this risk varies widely depending on the etiology (Table. Risk stratification following syncope). The Calgary score may be useful in the identification of patients with vasovagal syncope (Table. Calgary Syncope Symptom Score).Evidence 1Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to imprecision and indirectness to other subgroups. Expósito V, Guzmán JC, Orava M, Armaganijan L, Morillo CA. Usefulness of the Calgary Syncope Symptom Score for the diagnosis of vasovagal syncope in the elderly. Europace. 2013 Aug;15(8):1210-4. doi: 10.1093/europace/eut042. Epub 2013 Mar 10. PubMed PMID: 23478089. The Osservatorio Epidemiologico sulla Sincope nel Lazio (OESIL) score and the San Francisco Syncope Rule (Table. Risk stratification scores (postsyncope)) are clinical rules that can be used to help identify the patients that should likely be hospitalized and may require further investigations to exclude a cardiac etiology.Evidence 2Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to imprecision and indirectness to patient-important outcomes. Serrano LA, Hess EP, Bellolio MF, et al. Accuracy and quality of clinical decision rules for syncope in the emergency department: a systematic review and meta-analysis. Ann Emerg Med. 2010 Oct;56(4):362-373.e1. doi: 10.1016/j.annemergmed.2010.05.013. Review. PubMed PMID: 20868906; PubMed Central PMCID: PMC2946941. Del Greco M, Cozzio S, Scillieri M, Caprari F, Scivales A, Disertori M. Diagnostic pathway of syncope and analysis of the impact of guidelines in a district general hospital. The ECSIT study (epidemiology and costs of syncope in Trento). Ital Heart J. 2003 Feb;4(2):99-106. PubMed PMID: 12762272.

The Canadian Cardiology Society provides a list of major and minor risk factors predictive of short-term morbidity (Table. Risk stratification following syncope). They recommend that higher-risk patients (>1 major risk factor) be considered for further cardiac assessments (eg, echocardiogram and cardiologist consultation within 2 weeks).Evidence 3Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to a limited interstudy agreement on the specific factors listed. Major risk factors were arbitrarily defined as those independently identified in more than 1 publication and minor risk factors were identified in only 1 report. Sheldon RS, Morillo CA, Krahn AD, O'Neill B, Thiruganasambandamoorthy V, Parkash R, Talajic M, Tu JV, Seifer C, Johnstone D, Leather R. Standardized approaches to the investigation of syncope: Canadian Cardiovascular Society position paper. Can J Cardiol. 2011 Mar-Apr;27(2):246-53. doi: 10.1016/j.cjca.2010.11.002. Review. PubMed PMID: 21459273.

The subsequent management depends on the suspected cause of the syncope (Table. Syncope: Causes and management suggestions...).

Diagnostic Uncertainty and Symptom Recurrence Top

Recurrences of syncope are frequent. In patients with diagnostic uncertainty, further investigations can be considered. Tilt table testing, which provides a strong orthostatic stress to provoke vasovagal syncope, can be used in instances of undiagnosed recurrent syncope felt not to be of a cardiac or cerebrovascular origin.

A standard 24- to 48-hour Holter monitor can also be considered; however, unless the episodes are happening daily to weekly, there is little chance that a syncopal event will be recorded. A 1-month event recorder or an implantable loop recorder (ILR) could be used in selected patients soon after the initial encounter if there is diagnostic uncertainty with ongoing symptom reoccurrence.Evidence 4Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). Moderate Quality of Evidence (moderate confidence that we know true effects of the intervention). Quality of Evidence lowered due to the observational nature of the study but increased due to the large proportion of patients in whom the nature of syncope was explained. The findings apply to that specific population of patients. Edvardsson N, Frykman V, van Mechelen R, et al; PICTURE Study Investigators. Use of an implantable loop recorder to increase the diagnostic yield in unexplained syncope: results from the PICTURE registry. Europace. 2011 Feb;13(2):262-9. doi: 10.1093/europace/euq418. Epub 2010 Nov 19. PubMed PMID: 21097478; PubMed Central PMCID: PMC3024039. Furukawa T, Maggi R, Bertolone C, Fontana D, Brignole M. Additional diagnostic value of very prolonged observation by implantable loop recorder in patients with unexplained syncope. J Cardiovasc Electrophysiol. 2012 Jan;23(1):67-71. doi: 10.1111/j.1540-8167.2011.02133.x. Epub 2011 Jul 21. PubMed PMID: 21777327.

TablesTop

Table. Syncope: Causes and management suggestions

Etiology

Causes

Triggers

Diagnosis

Management

VVS

– Inappropriate reflex response leading to vasodilation or bradycardia

– Most common type of syncope in all ages (46% of all events)

– Usually benign and not requiring specific treatment. Ensure adequate salt intake and hydration

– Sudden, unexpected, or unpleasant stimulus (sight, sound, smell, pain)

– Following long periods of standing in crowded, hot places

– After meals; concomitant nausea or vomiting

– Typical history

– Calgary symptom score (see Table. Calgary Syncope Symptom Score)

– Tilt table can be considered if diagnostic uncertainty

– Avoidance of triggers

– Advise on episodic management (sitting down, isometric exercises)

– Orthostatic training (unproven benefit)

– In selected patients with episodes of prolonged asystole dual-chamber pacemaker is indicated

Carotid sinus syndrome

– Hypersensitivity of afferent or efferent limbs of carotid sinus leading to bradycardia and/or vasodilation

– Rarely in adults aged <50 years

– Syncope after head turning (eg, changing traffic lanes)

– Carotid sinus massage

– Asystole >3 s or fall in SBP >50 mm Hg

– Dual-chamber pacemaker

– Pharmacotherapy only in exceptional cases with specialist consultation (unproven benefit)

Orthostatic hypotension

Occurs when autonomic sympathetic vasomotor system fails to respond to challenges imposed by upright position, causing hypotension

– Primary causes: Parkinson disease, MSA, pure autonomic failure

– Secondary causes (more common): volume depletion: alcohol, drugs (diuretics, beta and alpha blockade, vasodilators)

– Sustained drop in BP (≥20 mm Hg drop in SBP, or SBP <90 mm Hg) within 3 min of standing

– Consistent medical history

– Discontinue offending drugs

– Avoid circumstances that may trigger syncope

– Increase intravascular volume with fluids or drugs: fludrocortisone 0.1-0.4 mg/d po or midodrine 5-40 mg/d po

Cardiac syncope

Can be structural or arrhythmogenic, leading to decreased cardiac output and drop in cerebral perfusion

– Significant organic heart disease; syncope during physical exercise or in supine position; syncope preceded by palpitations; family history of SCD

– Patients at high risk for VTE

– ECG or telemetry changes of conduction delay, QT prolongation, IHD, hypertrophy

– Echocardiogram

– Referral to cardiology for management of underlying cardiac disease

– Interrogate pacemaker if in situ

Cerebrovascular syncope

– Decreased cerebrovascular blood flow, can occur with:

1) Subclavian steal syndrome

2) TIA affecting vertebral and posterior arteries

3) Migraine variant

– Subclavian steal syndrome: stenosis of subclavian artery proximal to vertebral artery causing reversal of flow during strenuous upper limb exercise

– Ischemic risk factors (hypertension, dyslipidemia, prior CVA, smoker, DM)

– Migraine triggers

– Subclavian and/or carotid artery bruit, BP differential

– Ultrasonography of carotids

– Vertebral and subclavian angiography

– MRA/MRI

– Referral to specialists for management of underlying disease depending on etiology (eg, neurology for migraines, TIA; vascular surgery for subclavian steal)

BP, blood pressure; CVA, cerebrovascular accident; DM, diabetes mellitus; ECG, electrocardiography; IHD, ischemic heart disease; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging; MSA, multiple system atrophy; po, oral administration; SBP, systolic blood pressure; SCD, sudden cardiac death; TIA, transient ischemic attack; VTE, venous thromboembolism; VVS, vasovagal syncope.

Table. Risk stratification following syncope

Major risk factors

Abnormal ECG

Any bradyarrhythmia, tachyarrhythmia, or conduction disorder, ischemia or a history of myocardial infarction

History of cardiac disease

Ischemic, arrhythmic, obstructive, valvular

Hypotension

Systolic blood pressure <90 mm Hg

Minor risk factors

Cerebrovascular disease

Family history of sudden cardiac death

At age <50 years

Specific situations

Syncope while supine, during exercise, or no prodromal symptoms

Table. Calgary Syncope Symptom Score

Individual items of the Calgary Syncope Symptom Score

Points if “YES”

Is there a history of at least one of the following: bifascicular block, asystole, supraventricular tachycardia, diabetes mellitus?

–5

At times, have bystanders noted you to be blue during your faint?

–4

Did your syncope start when you were 35 years of age or older?

–3

Do you remember anything about being unconscious?

–2

Do you have lightheaded spells or faint with prolonged sitting or standing?

1

Do you sweat or feel warm before a faint?

2

Do you have lightheaded spells or faint with pain or medical settings?

3

The diagnosis of vasovagal syncope is made if the score is ≥–2.

Table. Risk stratification scores (postsyncope)

San Francisco Syncope Rule

OESIL risk score

Risk factors

– Systolic blood pressure <90 mm Hg

– Shortness of breath

– ECG: Nonsinus or new changes

– Hematocrit <30%

– Age >65

– History of cardiovascular disease

– Syncope without a prodrome

– Abnormal ECG findings

Assessed endpoint

7-day morbidity and mortality after presentation to an emergency department

1-year mortality

– No factors present: 0.3%

– >1 factor present: 15.2%

– 0-1 factor (low risk): 0.6%

– 2-4 factors (high risk): 31%

Score accuracy

– Sensitivity 98%

– Specificity 56%

– LR+: 2.9

– LR–: 0.03

– Sensitivity 97%

– Specificity 73%

– LR+: 3.6

– LR-: –0.11

LR+, positive likelihood ratio; LR–, negative likelihood ratio; OESIL, Osservatorio Epidemiologico sulla Sincope nel Lazio.

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