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For further information, see CMDT Part 10-39: Syncope

Key Features

  • Transient loss of consciousness and postural tone for few seconds pla

  • 30% of adults will experience ≥ 1 syncopal episode

  • High risk features include history of structural heart disease, abnormal ECG, and age > 60 years

Clinical Findings

Reflex (neurally mediated)

  • Caused by excessive vagal tone or impaired reflex control of the peripheral circulation

  • Vasovagal syncope ("common faint") most common

    • Often initiated by stressful situations

    • Common premonitory symptoms

      • Nausea

      • Diaphoresis

      • Tachycardia

      • Pallor

  • Other varieties: carotid sinus hypersensitivity, postmicturition, or cough syncope


  • Caused by impaired vasoconstrictive response to assuming upright posture, leading to abrupt decrease in venous return

  • Occurs in

    • Advanced age

    • Diabetes or other cause of autonomic neuropathy

    • Blood loss or hypovolemia

    • Vasodilator, diuretic, or adrenergic-blocker therapy


  • Caused by

    • Rhythm disturbances (sick sinus syndrome, atrioventricular (AV) block, tachyarrhythmias)

    • Mechanical causes (aortic or pulmonary stenosis, hypertrophic obstructive cardiomyopathy, pulmonary hypertension, atrial myxoma)

  • Episodes are often exertional


  • Examine for orthostatic changes in BP and pulse, cardiac abnormalities, and response to carotid sinus massage

  • Specific cause found on initial examination in only 50%

  • Resting ECG is recommended for all patients undergoing evaluation for syncope

    • High-risk findings include non-sinus rhythm, complete or partial left bundle branch block, and voltage criteria indicating left ventricular hypertrophy

    • When initial evaluation suggests a possible cardiac arrhythmia, continuous ambulatory ECG monitoring, event recorder (for infrequent episodes), or wearable implantable cardiac monitor can be considered

  • Do tilt-table testing before invasive studies unless clinical and ambulatory ECG evaluation suggests a cardiac cause


  • Characteristic history

  • Tilt-table testing

    • May be useful in patients with suspected vasovagal syncope where the diagnosis is unclear after initial evaluation, especially when syncope is recurrent

    • Hemodynamic response to tilting determines whether there is a cardioinhibitory, vasodepressor, or mixed response

    • The overall utility of the test is improved when there is a high pretest probability of neurally mediated syncope


  • > 20 mm Hg decline in BP immediately on standing

  • Tilt-table testing and Valsalva maneuver are diagnostic


  • Echocardiography to rule out mechanical causes

  • If rhythm disturbance suspected, ambulatory ECG monitoring indicated; may need to repeat several times, up to 3 days

  • Event recorder and transtelephone ECG monitoring indicated for more infrequent presyncopal episodes

  • Electrophysiologic studies indicated for

    • Recurrent episodes

    • Nondiagnostic ambulatory ECGs

    • Ischemic cardiomyopathy



  • Counterpressure maneuvers (squatting, leg-crossing, abdominal contraction) can be helpful in limiting or terminating episodes

  • Medical therapy is reserved for patients with symptoms despite these measures

    • Midodrine, an α-agonist

      • Can increase the peripheral sympathetic neural outflow ...

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