Syncope differentials

• The causes of syncope are broadly divided into four major categories:

  • Reflex syncope (e.g. vasovagal - most common cause in young people)
  • Orthostatic hypotension (fall in blood pressure on standing)
  • Arrhythmias (e.g. ventricular tachycardia, heart block)
  • Structural cardiopulmonary disease (e.g. aortic stenosis, HOCM, massive pulmonary embolism)
• Reflex syncope:

  • Due to a reflex response in the autonomic nervous system
  • Typically a clear history of clear prodromal symptoms in response to an external trigger - light-headedness, sweating
  • Vasovagal (most common) - often due to stressful event
  • Situational syncope - coughing, sneezing, micturition
  • Carotid sinus syndrome - exaggerated response to carotid sinus baroreceptor stimulation (lowers BP)
• Factors that can increase the risk of orthostatic hypotension include:

  • Older age (often due to reduced baroreceptor activity)
  • Medications (e.g. antihypertensives, vasodilatory drugs, tricyclic antidepressants)
  • Volume depletion
  • Autonomic dysfunction (e.g. Parkinson’s disease, diabetes mellitus)
• Lying/standing BP:

  • Lie down for 5 minutes and measure BP
  • Stand and measure BP after 1 minute
  • Measure BP again at 3 minutes
• Structural cardiopulmonary disease:

  • Cardiac outflow obstruction can lead to reduced cerebral perfusion - these causes often characterised by little or no prodromal symptoms with sudden syncope = aortic stenosis and HOCM
  • Low flow states secondary to severe heart failure or valvular regurgitation can result in syncope
  • Syncope may also occur from major cardiopulmonary events such as massive PE, acute MI, and aortic dissection - usually associated with severe chest pain and systemic symptoms