Syncope

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Definition

Syncope is a transient loss of consciousness (TLOC) due to global cerebral hypoperfusion characterized by rapid onset, short duration and spontaneous complete recovery. This excludes other causes of TLOC such as neurological, psychological and metabolic causes.

Classification

Syncope can be classified into:

• Reflex syncope
  • Vasovagal
    • mediated by orthostatic or emotional stress
  • Situational
    • Cough
    • Sneeze
    • Gastro-intestinal (swallow, defaecation, visceral pain)
    • Micturation
    • Post-exercise
    • Post-prandial
    • Others (e.g. laugh, brass instrument playing, weightlifting)
  • Carotid sinus syncope
  • Atypical forms
    • without apparent triggers and/or atypical presentation
• Syncope due to orthostatic hypotension
  • Primary autonomic failure
    • Pure autonomic failure
    • Multiple system atrophy
    • Parkinson's disease with autonomic failure
    • Lewy body dementia
  • Secondary autonomic failure
    • Diabetes
    • Amyloidosis
    • Uraemia
    • Spinal cord injuries
  • Drug induced orthostatic hypotension
    • Alcohol, vasodilators, diuretics, phenotiazines, antidepressants
  • Volume depletion
    • Haemorrhage, diarrhoea, vomiting etc.
• Cardiac syncope
  • Arrhythmias
    • Bradycardia: sinus node dysfunction, atrio-ventricular conduction system disease, implanted device malfunction.
    • Tachycardia: supraventricular, ventricular (idiopathic, secondary to structural heart disease or to channelopathies)
    • Drug-induced arrhythmias
  • Structural heart disease
    • Cardiac: cardiac valvular disease (or prosthetic valve dysfunction), acute myocardial infarction/ischemia, hypertrophic cardiomyopathy, cardiac masses, pericardial disease/tamponade, congenital anomalies of coronary arteries
    • Other: pulmonary embolus, acute aortic dissection, pulmonary hypertension

Pathophysiology

(Figure pathophysiology syncope)

Epidemiology

Syncope is common in the general population. The life-time cumulative incidence of ≥1 syncopal episodes in teenagers in the general population is high, with about 40 % by the age of 21 years. Reflex syncope is by far the most common cause. The majority have experienced reflex-mediated syncope episodes as teenagers and adolescents. The frequency of orhtostatic hypotension and cardiac syncope increases with age. Approximately 10-30% of the syncope episodes in patients above 60 years visiting a hospital for their syncope episodes are of cardiac origin.

Reflex syncope

Diagnostic evaluation

Reflex syncope refers to a heterogeneous group of conditions in which there is a relatively sudden change in autonomic nervous system activity (decreased sympathic tonus causing less vasoconstriction and increased parasympathic (vagal) tonus causing bradycardia), triggered by a central (e.g. emotions, pain, blood phobia) or peripheral (e.g. prolonged orthostasis or increased carotid sinus afferent activity). It leads to a fall in blood pressure and cerebral perfusion. The range of bradycardia varies widely in reflex syncope, from a small reduction in peak heart rate to several seconds of asystole. As reflex syncope requires a reversal of the normal autonomic outflow, it usually occurs in people with a functional autonomic nervous system and should therfore be distinguished from syncope due to neurogenic orthostatic hypotension in patients with chronic autonomic failure.

Adequate history taking reveals the clinical features associated with a syncopal event that are important to differentiate the different causes of syncope. Vasovagal syncope, a specific form of reflex syncope, is diagnosed if syncope is precipitated by emotional distress or orthostatic stress and is associated with typical prodrome (such as nausea, warmth, pallor, lightheadedness, and/or diaphoresis).

Treatment

The prognosis of reflex syncope is excellent. However, syncope episodes can have a considerable impact on quality of life, because of its unexpected nature and fear for recurrences. Initial treatment of reflex syncope consists of non-pharmacological treatment measures, including reassurance regarding the benign nature of the condition, increasing the dietary salt and fluid intake, moderate exercise training, and physical counterpressure maneuvres (muscle tensing).

Orthostatic hypotension

Diagnostic evaluation

Orthostatic hypotension is a sustained reduction of systolic blood pressure of at least 20 mmHg or diastolic blood pressure of 10 mmHg within 3 min of standing or head-up tilt to at least 60 degree on a tilt table. Orthostatic hypotension is a clinical sign and may be symptomatic or asymptomatic.