What are the main types of orthostatic syncope, specifically orthostatic hypotension (OH) and postural orthostatic tachycardia syndrome (POTS)?

Main Types of Orthostatic Syncope

The main types of orthostatic syncope are orthostatic hypotension (with several subtypes) and postural orthostatic tachycardia syndrome (POTS). 1

Types of Orthostatic Hypotension (OH)

Orthostatic hypotension can be classified into several distinct subtypes:

1. Initial (immediate) OH

   • Characterized by BP decrease >40 mmHg systolic and/or >20 mmHg diastolic within 15 seconds of standing 1
   • BP spontaneously returns to normal quickly (<40 seconds) 1
   • Symptoms include brief light-headedness and visual disturbances immediately after standing 1
   • More common in young, asthenic individuals and older adults taking alpha-blockers 1

2. Classical OH

   • Defined as sustained decrease in systolic BP ≥20 mmHg, diastolic BP ≥10 mmHg, or sustained decrease in systolic BP to <90 mmHg within 3 minutes of standing 1
   • In patients with supine hypertension, a systolic BP drop ≥30 mmHg should be considered 1
   • Symptoms include dizziness, light-headedness, fatigue, weakness, and visual/hearing disturbances 1
   • Associated with increased mortality and cardiovascular disease prevalence 1
   • Common in frail elderly, patients with autonomic failure, and those taking vasoactive drugs or diuretics 1

3. Delayed OH

   • Occurs beyond 3 minutes of standing 1
   • Characterized by slow progressive decrease in BP 1
   • Absence of bradycardia helps differentiate it from reflex syncope 1
   • May eventually trigger reflex syncope 1
   • More common in elderly persons due to stiffer hearts and impaired compensatory vasoconstrictor reflexes 1

4. Neurogenic OH

   • A subtype of OH due to dysfunction of the autonomic nervous system 1
   • Not solely due to environmental triggers like dehydration or medications 1
   • Due to lesions involving central or peripheral autonomic nerves 1
   • Orthostatic HR increase is blunted (usually <10 bpm) because autonomic HR control is impaired 1

Postural Orthostatic Tachycardia Syndrome (POTS)

• Defined as sustained heart rate increase of ≥30 beats per minute (≥40 bpm in adolescents aged 12-19) within 10 minutes of standing or head-up tilt, WITHOUT orthostatic hypotension 1, 2
• Heart rate often exceeds 120 bpm during standing 1, 2
• Characterized by symptoms of orthostatic intolerance: light-headedness, palpitations, tremor, weakness, blurred vision, and fatigue 1, 2
• Symptoms typically develop upon standing and are relieved by sitting or lying down 1
• Syncope is rare in POTS and usually elicited by vasovagal reflex activation 1
• More common in young women, often following infection or trauma 1
• Frequently associated with:
  • Deconditioning 1, 3
  • Immune-mediated processes 1
  • Excessive venous pooling 1
  • Hyperadrenergic state 1, 3
  • Chronic fatigue syndrome 1
  • Joint hypermobility syndrome 1, 2

Orthostatic Vasovagal Syncope

• While not typically classified as a primary form of orthostatic syncope, orthostatic vasovagal syncope can occur due to prolonged standing 1
• Involves a vasovagal reflex triggered by progressive blood pooling 1
• Characterized by autonomic activation symptoms (nausea, pallor, sweating) preceding syncope 1
• More common in women 1
• May be associated with chronic orthostatic intolerance 1

Diagnostic Considerations

• Active standing test or tilt-table testing is essential for diagnosing these conditions 1, 2
• POTS can only be diagnosed in the absence of orthostatic hypotension 1, 2
• In classical OH, HR increase is preserved or enhanced in OH due to hypovolemia, but blunted in neurogenic OH 1
• Approximately 51% of POTS patients also experience initial orthostatic hypotension, compared to only 13% of healthy controls 4

In conclusion, orthostatic syncope encompasses both orthostatic hypotension (with its various subtypes) and postural orthostatic tachycardia syndrome, each with distinct pathophysiological mechanisms and clinical presentations.