Type of syncope	Scenario	Clinical features
Reflex (neurogenic; 35% to 48% of cases*)
Carotid sinus hypersensitivity	Associated with pressure on the neck, such as shaving, wearing a tight collar, and turning the head; consider in patients with unexplained falls	Stimulation of the carotid sinus can cause ventricular pause or a drop in systolic blood pressure, which is reproducible with carotid sinus massage
Situational	Occurs during or after defecation, urination, or coughing, or after eating or exercise	Absence of heart disease; patient has likely had previous similar experiences
Vasovagal	Inappropriate (nonphysiologic) vasodilation and bradycardia; caused by fear, pain, noxious stimuli, heat, or stress	May have prodromal features, such as nausea, warmth, or diaphoresis
Cardiac (5% to 21% of cases*)
Arrhythmia	Palpitations may precede syncope; sometimes lacks prodrome; may be unprompted	Abnormal electrocardiographic findings (e.g., bradyarrhythmias, tachyarrhythmias, pacemaker dysfunction); family history of sudden death; personal history of heart disease; abrupt onset of palpitations or symptoms while supine or prone
Structural	Cardiac tamponade	Hypotension, tachycardia, increased jugular venous pressure, pulsus paradoxus
	Hypertrophic cardiomyopathy	Family history of sudden cardiac death, systolic murmur that intensifies during Valsalva maneuver
	Infiltrative diseases (e.g., amyloidosis, sarcoidosis, hemochromatosis)	Arrhythmias, heart block, heart failure
Valvular	Aortic, mitral, or pulmonic stenosis	Symptoms depend on severity; may cause heart failure, exertional angina; murmur may be heard on examination
Vascular (may be associated with electrocardiographic changes)	Acute myocardial infarction or ischemia	Chest pain, diaphoresis, shortness of breath, onset with exertion
	Aortic dissection	Hypotension or shock, severe sharp chest pain that possibly radiates to the back
	Pulmonary embolism	Shortness of breath; fatigue; may be asymptomatic
Orthostatic (4% to 24% of cases*)
Autonomic failure	Neurogenic-mediated orthostasis; failure of autonomic nervous system to compensate for positional changes	May be seen in patients with Parkinson disease, Lewy body dementia, multiple sclerosis, diabetes mellitus, connective tissue disorders, advanced age, or spinal cord injury
Drug-induced	Numerous medications may cause vasodilation or decreased cardiac output	Recent initiation or increased dose of medications (consider anticholinergics, diuretics, antihypertensives, dopaminergics, opiates, antipsychotics, sedatives, and tricyclic antidepressants)
Postural orthostatic tachycardia syndrome	Common in young adults; more common in females	Severe orthostasis with marked tachycardia
Volume depletion	Caused by poor oral intake, gastrointestinal losses, acute blood loss, and diuretics	History of blood or fluid loss; low blood pressure; elevated heart rate