• Syncope is a sudden transient loss of consciousness (LOC) with spontaneous complete recovery. Near syncope is considered equivalent to syncope.
• 7-day risk of serious adverse outcome is 10% and death is 1/250¹.
• Despite several risk stratification rules (below),  the best diagnostic tools remain: careful history, thorough physical exam, and ECG and good clinical judgement.

Cardiac

Mortality >10% at 6 months.

• Arrhythmias: Most common cause of cardiac syncope.
  • No prodrome.
  • Sudden LOC and may report palpitations prior to the event.
  • Occurs in any position.
  • Family history of arrhythmia, inherited cardiac disorders, sudden unexplained cardiac death, drowning, unexplained seizures.

Syncope in the setting of exercise is due to cardiac arrhythmia until proven otherwise.

• Structural lesions:
  • Valvular and cardiomyopathies: murmurs or signs of CHF require further workup – often need echocardiogram.
  • Pulmonary emboli unlikely to present as an isolated syncope given that if there is enough clot burden to obstruct the blood flow, there should be other findings such as SOB, tachycardia, ECG changes.
• Ischemia: Infrequent cause (<3%) and often will have concomitant findings (such as massive STEMI on ECG or classic CP).

Orthostatic

Autonomic system fails to maintain blood pressure with increased heart rate.  Often have positional component, such as onset when standing up from sitting position.

• Orthostatic vital signs neither sensitive nor specific and cannot be used in isolation to rule in or out this as cause of syncope.
• Medications: Antihypertensives, diuretics, antidepressants, beta-blockers, alpha-blockers.
• Postprandial hypotension: onset shortly after a meal.
• Intravascular volume loss: dehydration (vomiting, diarrhea, decreased po intake), hemorrhagic (GI, occult trauma, AAA, splenic rupture, retroperitoneal bleeds, etc).

*** SO MAY NOT BE THAT BENIGN AFTER ALL –> thorough exam, including rectal for melena and bedside US for AAA, in appropriate settings and in elderly/high-risk patients

Reflex-mediated

Autonomic system acts inappropriately resulting in reflex bradycardia and vasodilation. Benign cause of syncope with excellent prognosis.

• Vasovagal: prodrome, induced by emotion or pain.
• Situational: cough, micturition, defecation.
• Carotid sinus hypersensitivity: older, male, stimulation of carotid sinus (necktie, shaving, etc).

Neurologic

Transient interruption of blood flow to the brain stem or cerebral cortex.

• Isolated syncope is rare (<1%).
• Routine use of CT head for syncope is not indicated.
• TIA and SAH patients have additional symptoms such as headache (SAH) and/or posterior circulation neurological findings (vertebrobasilar TIA).
• Subclavian steal syndrome – stenotic subclavian artery receives additional blood from the vertebral artery drawing it away from the brainstem. There often will be a difference in the blood pressure in each arm and additional posterior circulation deficits. Patient may report using the affected arm prior to the syncope.

ECG

Only mandatory test for all syncope patients.

• Ottawa group found that the patients were at risk for cardiac outcome within 30 days if any of the following were present: (see below related resources)
• Ottawa ECG Criteria³:
  • High degree blocks (2nd degree type II or 3rd degree AV)
  • Bundle branch + 1st degree block
  • RBB + left anterior or posterior block
  • Ischemic changes
  • Non-sinus rhythm
  • Left axis deviation
  • ED cardiac monitor abnormalities

• Above ECG criteria likely to under-represent those with rare diagnosis, such as channelopathies, cardiomyopathies, and other inherited arrhythmogenic conditions. Therefore, ECGs (particularly those of younger patients) should be carefully examined for the following abnormalities:
  • Long QTc
  • Wolff Parkinson White
  • Brugada
  • Arrhythmogenic Right Ventricular Cardiomyopathy
  • Hypertrophic Cardiomyopathy (HCM)
  • Bifascicular Block
  • 3rd Degree AV Block
  • Type 2 2nd Degree AV Block

Other Investigations²

• Investigations beyond ECG are required in cases where serious etiology is suspected or where it is not possible to determine the exact cause of syncope based solely on history and physical exam. These may include blood work, CXR, echocardiogram, telemetry, or Holter monitoring. The choice of the investigations is based on the presentation.

Risk Stratification Tools

Most risk stratification rules either have significant limitations or are awaiting validation. The Canadian Syncope Risk Score is currently awaiting validation. Perhaps the most studied is San Francisco Syncope Rule:

San Francisco Syncope Rule Criteria⁴

Congestive Heart Failure History

Hematocrit < 30%

ECG Abnormal?

Shortness of Breath History

Systolic BP < 90 mmHg at Triage

Important: Pooled sensitivity was 86%.  1.4% of patients who are San Francisco Rule negative will have an adverse event at 7 days. Majority (60%) of missed diagnosis were arrhythmias. Also the rule did not exclude patients for whom the cause of the syncope was obvious, therefore making it unclear if this can be applied to undifferentiated syncope patients¹.

Canadian Syncope Risk Score 

Important: Apply this score when there is a doubt as to potential etiology of syncope. The score predicts adverse events in the next 30 days (versus 7 days in San Francisco Rule). Patients with high score will require further evaluation⁵.

1. Risk Assessment: Syncope in the Emergency Department. The NNT

   
   

2. Ouyang H, Quinn J. Diagnosis and Evaluation if Syncope in the Emergency Department. Emerg Med Clin N Am 28 (2010) 471–485

   
   

3. Thiruganasambandamoorthy  V, Hess EP, Turko E, Tran M, Wells GA, Stiell IG. Defining Abnormal Electrocardiography in Adult Emergency Department Syncope Patients: The Ottawa Electrographic Criteria.  CJEM 2012;14(4):248-258

   
   

4. Quinn JV, Stiell IG, McDermott DA, et al. Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes. Ann Emerg Med. 2004;43:224-232.

   
   

5. Thiruganasambandamoorthy  V, Kwong K, Wells GA, Sivilotti MLA, Mukarram M, Rowe BH, Lang E, Perry JJ, Sheldon R, Stiell IG, Taljaard M. Development of the Canadian Syncope Risk Score to predict serious adverse events after emergency department assessment of syncope. CMAJ September 6, 2016 vol. 188 no. 12