Syncope

Syncope is a clinical syndrome characterised by transient loss of consciousness and postural tone that is most often due to temporary and spontaneously self-terminating global cerebral hypoperfusion.¹ The term syncope excludes seizures, coma, shock, or other states of altered consciousness.²

• Syncope affects 30% of adults at some point in their lives.
• The incidence peaks in 15-19 year-olds and is more common in females than males.³
• There is a second peak in people in their sixties and seventies.

• Neurally-mediated (reflex):
  • Vasovagal syncope (common faint)
  • Carotid sinus syncope
  • Situational syncope, e.g. cough, sneeze, gastrointestinal stimulation (swallow, defaecation, visceral pain), micturition
  • Glossopharyngeal neuralgia
• Orthostatic hypotension:
  • Autonomic failure
  • Post-exercise
  • Post-prandial
• Drugs, alcohol.
• Volume depletion: haemorrhage, diarrhoea, Addison's disease.
• Cardiac arrhythmias as primary cause, e.g. sinus node dysfunction, AV conduction system disease, paroxysmal SVT and VT, inherited syndromes (e.g. long QT syndrome, Brugada syndrome), pacemaker or implantable cardioverter-defibrillator malfunction.
• Structural cardiac or cardiopulmonary disease:
  • Obstructive cardiac valvular disease
  • Acute myocardial infarction or ischaemia
  • Obstructive cardiomyopathy
  • Atrial myxoma
  • Acute aortic dissection
  • Pericardial disease or tamponade
  • Pulmonary embolus or pulmonary hypertension
• Cerebrovascular:
  • Vascular steal syndromes
• Anxiety, panic attacks, hyperventilation.

• A careful history, physical examination (including standing and supine blood pressure and pulse and full cardiovascular examination) combined with an ECG will yield a diagnosis in 50% of cases.⁵
• Initial evaluation may lead to a certain diagnosis based on symptoms, physical signs, or ECG findings. However syncope is often multifactorial, especially in older individuals.
• Classical vasovagal syncope is diagnosed if precipitating events such as fear, severe pain, emotional distress or prolonged standing are associated with typical prodromal symptoms.
• Situational syncope is diagnosed if syncope occurs during or immediately after urination, defaecation, cough or swallowing.
• Orthostatic syncope is diagnosed when there is evidence of orthostatic hypotension (a decrease in systolic blood pressure 20 mm Hg or a decrease of systolic blood pressure to <90 mm Hg) associated with syncope or presyncope.
• Cardiac ischaemia-related syncope is diagnosed when symptoms are present with ECG evidence of acute ischaemia.
• Arrhythmia-related syncope is diagnosed by ECG when there is:
  • Sinus bradycardia of less than 40 beats/min or repetitive sinoatrial blocks or sinus pauses greater than 3 seconds in the absence of negative chronotropic medications
  • Second degree Mobitz II or third degree atrioventricular block
  • Alternating left and right bundle branch block
  • Rapid paroxysmal SVT or VT
  • Pacemaker malfunction with cardiac pauses

In the absence of an obvious diagnosis, the following may indicate a likely underlying cause:

• Neurally-mediated syncope:
  • Absence of cardiac disease
  • Long history of syncope
  • Syncope occurring:
    • After sudden unexpected unpleasant sight, sound, smell or pain
    • With prolonged standing or crowded, hot places
    • Associated with nausea and/or vomiting
    • During or shortly after a meal
    • With head rotation, pressure on carotid sinus (as in tumours, shaving, tight collars)
    • Following exertion
• Syncope caused by orthostatic hypotension:
  • After standing up
  • Following the start of medication leading to hypotension or changes of dosage
  • With prolonged standing especially in crowded, hot places
  • Presence of autonomic neuropathy or parkinsonism
  • Following exertion
• Cardiac syncope:
  • Presence of severe structural heart disease
  • During exertion, or supine
  • Preceded by palpitation or accompanied by chest pain
  • Family history of sudden death
• Cerebrovascular syncope:
  • With arm exercise
  • Differences in blood pressure or pulse in the two arms

Causes of non-syncopal attacks:⁴

• Disorders without any impairment of consciousness, e.g. falls, cataplexy, drop attacks, psychogenic pseudo-syncope, transient ischaemic attacks of carotid origin.
• Disorders with partial or complete loss of consciousness.
  • Metabolic disorders, e.g. hypoglycaemia, hypoxia, hyperventilation with hypocapnia
  • Epilepsy
  • Narcolepsy
  • Intoxications
  • Vertebro-basilar transient ischaemic attack

• Initial testing in primary care includes:
  • Fasting glucose (hypoglycaemia), full blood count (anaemia) and ECG
• Further investigations in secondary care include:⁴
  • Neurally-mediated syncope: carotid sinus massage, tilt testing,⁶ implantable loop recorder
  • Cardiac syncope: echocardiogram, Holter/external loop monitoring,⁷ electrophysiological test, exercise stress testing⁸ and implantable loop recorder
• Tests that are less useful but may be indicated include:⁴
  • Epilepsy and TIA: electroencephalography (EEG), Brain CT/MRI
  • Cardiac: carotid doppler sonography, coronary angiography, pulmonary CT/scintigraphy

• Most patients with syncope require only reassurance and education regarding the nature of the disease and the avoidance of triggering events.
• Conservative measures include ensuring adequate fluid and salt intake and to sit or lie down when they experience warning symptoms.
• Referral is indicated if there is any suggestion of a serious underlying cause requiring investigation and management (especially any suggestion of a cardiovascular cause), or if the episodes of syncope cannot be controlled by simple avoidance of precipitating factors and general advice.
• The essential aspect of management is to establish the precise cause of the patient's episodes of syncope in order to provide appropriate treatment and advice.
• Venous support stockings may help.
• Reassess medications which may need either reduction in dosage or withdrawal.
• Oral fludrocortisone has been used to increase pre-load and make people less likely to lose consciousness when they stand.⁹
• Management of any underlying cause, e.g. pacemakers.

• Syncope may lead to physical injury.
• Syncope was found to be the cause of 21% (second highest behind epilepsy) of road accidents involving loss of consciousness at the wheel.⁸

• Approximately 35% of patients have recurrences of syncope at 3 years of follow-up.⁸
• In children and adolescents, syncope is a benign event. Isolated syncope (transient loss of consciousness in the absence of prior or concurrent neurological, coronary, or other cardiovascular disease) is not associated with any increased risk of transient ischaemic attack, stroke or myocardial infarction and is not associated with any excess of all-cause or cardiovascular mortality (including sudden death).¹⁰
• For patients with cardiac causes, generally an older group, 50% die within 5 years, a third of which due to sudden death.
• For non-cardiac causes of syncope, excluding children and adolescents, 5-year mortality is 30%.