Syncope

Overview

Syncope describes a transient loss of consciousness due to a decrease in blood flow to the brain. This is rapid in onset, lasts for a short period of time (mostly up to around 30 seconds), and people resolve spontaneously and completely recover.

This definition excludes other causes of a loss of consciousness, such as epilepsy, which may last longer and have a post-ictal period and more prolonged recovery.

Classification

Reflex (neurally-mediated) syncope

Reflex syncope occurs when the heart rate decreases and the blood vessels expand inappropriately following a trigger. It can be divided into:

• Vasovagal syncope – ‘fainting’:
  • Exposure to blood or unpleasant sight
  • Strong emotion
  • Pain
  • Stress
• Situational syncope – syncope caused by specific behaviours:
  • Coughing
  • Urination
  • Defecation
  • Vomiting
  • Swallowing
• Carotid sinus syncope:
  • Pressure on the carotid sinus can cause syncope in some individuals

Orthostatic syncope

This is syncope that occurs due to an excessive drop in blood pressure when standing up from sitting or lying down. Its causes include:

• Primary autonomic failure:
  • Causes include Parkinson’s disease, dementia with Lewy bodies, multiple system atrophy, other Parkinson’s plus syndromes
• Secondary autonomic failure:
  • Causes include diabetes mellitus, uraemia, spinal cord injuries, amyloidosis
• Drug-induced orthostatic hypotension:
  • Causes include diuretics, vasodilators, alcohol, antidepressants
• Volume depletion:
  • Causes include haemorrhage, diarrhoea, vomiting

Cardiac syncope

Cardiac syncope occurs due to arrhythmia, valvular heart disease, muscular heart disease, or vascular heart disease. Its causes include:

• Arrhythmia:
  • Bradycardia:
    • Sinus node dysfunction
    • Atrioventricular (AV) conduction disorders
    • Implanted device malfunction
  • Tachycardia:
    • Supraventricular
    • Ventricular
• Structural disease:
  • Cardiac disease:
    • Causes include: valvular disease, myocardial ischaemia/infarction, hypertrophic cardiomyopathy, cardiac masses (e.g. myxomas or other tumours), pericardial disease and cardiac tamponade, congenital heart disease, prosthetic valve dysfunction
  • Other causes:
    • Pulmonary embolism
    • Aortic dissection
    • Pulmonary hypertension

Investigations

Overview

Initial tests include:

• Lying-standing blood pressure:
  • Patient lies down for 5 minutes
  • Patient sits up/stands up and the blood pressure is recorded immediately, at 1 minute, then at 3 minutes
  • Orthostatic hypotension is defined as a drop in blood pressure of at least 20 mmHg systolic or 10 mmHg diastolic within 3 minutes of standing.
• ECG:
  • May identify arrhythmia
• Tilt-table testing:
  • If blood pressure measurements are inconclusive, a tilt-table test may be considered.
• 24-hour ECG monitoring:
  • May identify arrhythmia