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Box 9.2

Causes of Syncope

MechanismSubtypeComment
Reflex (neurally-mediated)Vasovagal

Typically follows pain, emotional distress or prolonged standing.

Diagnose when there are no features suggesting an alternative diagnosis, and the clinical features are concordant (Table 9.2).

SituationalDiagnose when there are no features suggesting an alternative diagnosis and syncope occurred in typical circumstances (e.g. micturition while standing, or a prolonged bout of coughing).
Carotid sinus hypersensitivity(CSH)Diagnose in patients aged 60 and over with TLoC, when there are no features suggesting an alternative diagnosis, and testing for CSH (Table 9.4) is positive.
Atypical formDiagnose when there no features suggesting an alternative diagnosis, testing for CSH is negative, and tilt-table testing provokes symptoms.
Orthostatic hypotensionPrimary autonomic failureFor example in multiple system atrophy, Parkinson's disease with autonomic failure.
Secondary autonomic failureFor example in diabetes mellitus or amyloidosis.
Drug-inducedMany drugs may cause or contribute to orthostatic hypotension, including alpha blockers, antidepressants, antihypertensive agents, drugs for Parkinson's disease and diuretics.
Volume depletionSee Chapter 2.
CardiovascularBradyarrhythmiaSee Chapter 44.
TachyarrhythmiaSee Chapters 40, 41, 42, 43.
Structural cardiac diseaseThis includes valve disease (notably severe aortic stenosis; see Chapter 51), congenital heart disease and cardiomyopathies. ECG and echocardiography typically show characteristic abnormalities.
Acute myocardial ischaemiaSee Chapters 45 and 46.
Aortic dissectionSee Chapter 50.
Pulmonary embolismSee Chapter 57.
Severe pulmonary hypertensionMay result in exertional syncope. There may be clinical signs of right ventricular failure (e.g. elevated jugular venous pressure). ECG and echocardiography typically show characteristic abnormalities.