Syncope is a transient loss of consciousness (T-LOC), due to global cerebral hypoperfusion (an inadequate supply of oxygen) characterised by

  • rapid onset/offset
  • short duration
  • spontaneous complete recovery

There are two reasons to evaluate patients presenting with syncope;

  • To identify the precise cause in order to find an effective method of specific treatment of the mechanism of syncope
  • To assess the risk to the patient, and treat the underlying disease, rather than the syncopal mechanism

Syncope is differentiated from T-LOC with the inclusion of cerebral hypoperfusion, so, the reason for the LOC, whereas a LOC is termed just so.

Usually, these blackouts last no longer than 20s, and are often warned of via:

  • dizziness
  • nausea
  • sweating
  • vision disturbances

Rarely, however, they can be of a longer duration; up to a number of minutes. Diagnosis of syncope is difficult in these instances, as it is easy to be incorrect in a differential. Generally, recovery from syncope results in the complete restoration of normal faculties and occasionally fatigue, save for elderly patients, who have been documented to suffer from a retrograde amnesia.

This algorithm, adapted from the European Society of Cardiology, provides diagnostic assistance.

Screenshot (163)


  • Describes symptoms which manifest  before LOC in syncope
  • A “warning”

Classification of Syncope

Reflex Syncope

  • Group of conditions
    • Multi-mechanism
  • Neurally mediated
  • Control of circulation is interrupted and arterial BP falls as a result of;
    • Vasodilation
    • Bradycardia

There are 4 principal types:

Vasovagal Syncope (common faint)

  • Mediated by;
    • Orthostatic stress
    • Emotion
  • Preceded by
    • Sweating
    • Nausea
    • Pallor

Situational Syncope

  • Specific circumstances, for example
    • Post-exercise
    • Valsalva
    • During blood-letting
  • In older patients, is often a precursor to autonomic failure and orthostatic hypertension

Carotid Sinus Syncope

  • Uncommon form can be triggered by carotid sinus massage
  • Common form can be diagnosed with carotid sinus massage

Atypical Form

  • Denotes reflex syncope in unclear or absent triggers
  • Diagnosis rests on exclusion of other forms of syncope and reproduction of syncope with Tilt Table Testing

Orthostatic Hypotension and Orthostatic Intolerance Syndromes

  • Abnormal decrease in systolic BP upon standing
  • Circulatory abnormality
    • Vasoconstriction deficiency
  • Symptoms include;
    • Lightheadedness
    • Dizziness
    • Pre-syncope
    • Fatigue
    • Precordial, neck or back pain
    • Hearing disturbance
    • Visual disturbance

There are 3 principal types:

Classical OH

  • Within 3 minutes of standing;
    • Systolic BP rise ≥ 20mmHg
    • Diastolic BP rise ≥ 10mmHg

Initial OH

  • Immediately on standing;
    • BP decrease > 40mmHg
  • Return to normal
    • < 30s

Progressive OH

  • Slow, progressive decrease in systolic BP
  • In elderly, may be followed by reflex syncope

Cardiac Syncope

  • Arrhythmias are the most common cardiac cause of syncope
  • Eventual syncope is influenced by numerous factors;
    • HR
    • CO
    • Arrhythmia type (ventricular or supraventricular)
    • LV function
    • Vascular compensation (or lack thereof)

Arrhythmias and disorders with known links to syncope;

  • Bradycardia
    • Sinus node disease
    • AV blocks
    • Cardiac implant malfunction
  • Tachycardia
    • Supraventricular
    • Ventricular
  • Drug Induced
  • Structural disorders
    • HCM
    • Cardiac tamponade
    • MI

In the case of AV Blocks, the more severe forms, such as Mobitz II and 3rd° Block are most closely related to syncope. Rhythm becomes reliant on secondary pacemaker sites, which are far less reliable than the SA node, and the delay between impulses is too great, resulting in syncope

Bradycardia is responsible for a prolongation of repolarisation, and increases the risk of ventricular tachycardia, most notably Torsades de Pointes. This becomes more significant when a patient is undergoing pharmaceutical treatment that may prolong the QT interval, with this also giving rise to Torsades. The syncopal episode typically begins at the start of the VT, before vascular compensation begins to restore haemostasis.

Treat the arrhythmia to treat the syncope


  • Carotid sinus massage
    • Patients > 40yrs
  • Echocardiography
    • If there is previous known heart disease
    • Assess heart structure
  • AmbECG monitoring
  • Tilt table testing