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

Orthostatic

• 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

Cardiogenic

• 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

Diagnosis

• 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

Reflex

• 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

Orthostatic

• > 20 mm Hg decline in BP immediately on standing

• Tilt-table testing and Valsalva maneuver are diagnostic

Cardiogenic

• 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

Treatment

Reflex

• 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 ...