Types of Cardiac Syncope

Underlying Mechanism

Examples of Underlying Causes
Arrhythmogenic syncope Brady-/Tachycardia → ↓ EF
  • Sick sinus syndrome
  • AV blocks (high grade)
  • Tachyarrhythmias: VT, SVT
Cardiovascular syncope Myocardial dysfunction
Cardiac outflow obstruction
  • Massive MI, ICM, HCM
  • AS, MVP, cardiac tamponade
  • PE, pHTN, asymmetric hypertrophy

Syncope

Gary Salomon

Background 

  • Definition of syncope: sudden, transient loss of consciousness with spontaneous recovery secondary to cerebral hypoperfusion 
  • Presyncope: symptoms that usually precede syncope (lightheadedness, visual symptoms, possibly altered consciousness without loss of consciousness); may or may not progress to syncope 
  • Convulsive syncope: can be present in any type of syncope in which LOC is accompanied by myoclonic movements mimicking seizure-like-activity 
  • Syncope Mimics: Seizure, stroke/TIA, subclavian steal, metabolic derangements, Intoxication/withdrawal, hypoglycemia, concussion 
  • These typically do not result in complete LOC with spontaneous recovery

Cardiac Syncope 

  • Common features: brief/no prodrome, palpitations, non-position dependent, family hx of SCD/premature death 
  • Cardiac and vascular causes of syncope have a higher chance of being life-threatening and should be ruled out first.

Noncardiac Syncope 

  • Common features: prodrome (nausea, vomiting, warmth), triggers with positional changes

Types of Noncardiac Syncope

Underlying Mechanism

Examples of Underlying Causes/Triggers
Vasovagal (neurocardiogenic) syncope Vasovagal response
  • Prolonged standing
  • Emotional stress, pain, injury
  • Heat exposure
  • Idiopathic
Situational syncope
  • Cough, Swallow, Laughing, Defecation
  • Micturition (seen in BPH)
Carotid sinus hypersensitivity Exaggerated PSNS response to carotid sinus stimulation
  • Pressure on carotid sinuses (e.g., massage, shaving, tight necktie)
Orthostatic syncope Orthostasis-related
  • Hypovolemia (hemorrhage, dehydration)
  • Medications (BB, alpha blockers, CCB)
  • Prolonged bed rest
  • Age-loss of baroreceptor sensitivity
  • Neurogenic orthostasis (Parkinson's, Diabetic neuropathy)
Postural tachycardia syndrome (POTS) Poorly understood; Often occurs following other medical conditions (e.g., pregnancy, trauma, surgery, viral illness)

Workup 

  • Important history: prodrome, LOC duration, witnesses, duration of post-LOC confusion, medications, 
  • Initial workup for all patients: EKG, orthostatic VS, CBC, BMP, POC glucose, UDS 
  • Consider if cardiac etiology suspected: troponin, BNP, TTE and stress testing particularly in exertional syncope 
  • EEG and neuroimaging if high concern for seizure activity or focal neuro deficit (neuro testing comes at high cost and low diagnostic yield) 
  • Consider based on clinical suspicion: A1C, Vitamin B12, iron studies, TSH, free light chains/SPEP/UPEP if concerned for amyloidosis

Management 

Dependent on suspected cause of syncope 

  • Cardiac: If arrhythmia is suspected but not captured on admission, consider discharge with event monitor Monitoring duration should be equal to or greater than the frequency of events (e.g. If the symptoms occur roughly once a month, monitoring duration should be at least a month) 
  • Noncardiac: see autonomics section
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