What are the main types of orthostatic syncope?

Main Types of Orthostatic Syncope

The main types of orthostatic syncope include initial orthostatic hypotension, classical orthostatic hypotension, delayed orthostatic hypotension, orthostatic vasovagal syncope, and postural orthostatic tachycardia syndrome (POTS). 1

Initial Orthostatic Hypotension (IOH)

• Characterized by a pronounced BP decrease (>40 mmHg systolic and/or >20 mmHg diastolic) immediately upon standing 1
• BP spontaneously and rapidly returns to normal within 30-40 seconds 1
• Symptoms include transient lightheadedness, dizziness, and visual disturbances occurring within seconds after standing 1
• Most common in young, asthenic subjects and elderly individuals 1
• May be exacerbated by alpha-blocker medications 1

Classical Orthostatic Hypotension (cOH)

• Defined as a sustained decrease in systolic BP ≥20 mmHg, diastolic BP ≥10 mmHg, or a sustained decrease in systolic BP to an absolute value <90 mmHg within 3 minutes of standing 1
• In patients with supine hypertension, a systolic BP drop ≥30 mmHg should be considered significant 1
• Characterized by a "concave" curve pattern of BP decrease after standing 1
• Orthostatic heart rate increase is typically blunted (<10 bpm) in neurogenic OH due to impaired autonomic HR control 1
• Associated with increased mortality and cardiovascular disease prevalence 1
• More common in elderly patients, those with autonomic failure, and patients taking vasoactive drugs or diuretics 1, 2

Delayed Orthostatic Hypotension (dOH)

• Defined as OH occurring beyond 3 minutes of standing 1
• Characterized by a slow progressive decrease in BP with variable heart rate compensation 1
• The absence of bradycardia helps differentiate it from reflex syncope 1
• May eventually trigger reflex syncope mechanisms 1
• More common in frail individuals and those with incipient autonomic failure 1
• Compared to classical OH, patients with delayed OH are typically younger, more often female, and have fewer comorbidities 2

Orthostatic Vasovagal Syncope

• Occurs due to a vasovagal reflex triggered by progressive blood pooling during prolonged standing 1
• Preceded by autonomic activation symptoms (nausea, pallor, sweating) 1
• More common in women 1
• May be associated with chronic orthostatic intolerance 1
• Differs from other forms of OH by the presence of both vasodepressive and cardioinhibitory components 1, 3

Postural Orthostatic Tachycardia Syndrome (POTS)

• Characterized by an excessive heart rate increase (≥30 bpm or to ≥120 bpm) within 10 minutes of standing, without orthostatic hypotension 1, 4
• In adolescents aged 12-19 years, the heart rate increase should be >40 bpm 4
• Associated with symptoms of orthostatic intolerance (lightheadedness, palpitations, tremor, weakness, blurred vision, fatigue) 4
• Syncope is rare and usually elicited by vasovagal reflex activation 1
• More common in young women, often following infection or trauma 1
• Frequently associated with joint hypermobility syndrome and chronic fatigue syndrome 1, 3

Clinical Approach to Diagnosis

• Active standing test or head-up tilt testing is essential for diagnosis of all forms of orthostatic syncope 1, 4
• Continuous monitoring of blood pressure and heart rate is necessary to differentiate between the various types 1
• For POTS diagnosis, a 10-minute active stand test with measurements at baseline, immediately upon standing, and at 2,5, and 10 minutes is recommended 4
• Autonomic function testing may help identify underlying neurogenic causes 1, 5

Management Considerations

• Non-pharmacological measures are fundamental for all types of orthostatic syncope 5, 3
• Maintain adequate hydration with 2-3 L of fluids per day and 10g of NaCl daily 5
• Physical counterpressure maneuvers, compression garments, and elevation of the head of the bed by 10° can be effective 5
• Pharmacological options vary by type:
  • Fludrocortisone (0.1-0.3 mg once daily) for volume expansion 5, 6
  • Midodrine (5-20 mg, three times daily) for vasoconstriction 5, 6
  • Beta-blockers should be used cautiously as they may worsen symptoms in dysautonomic syndromes 5

Pitfalls in Diagnosis and Management

• Failure to perform standing tests for adequate duration may miss delayed forms of OH 4
• Not distinguishing between the different types of orthostatic syncope can lead to inappropriate treatment 4
• Supine hypertension is a common complication in patients with neurogenic OH and must be considered when initiating treatment 6
• Medications, especially vasoactive drugs and diuretics, are common contributors to all forms of orthostatic syncope 1, 5