What are the causes of orthostatic tachycardia?

Causes of Orthostatic Tachycardia

Orthostatic tachycardia is primarily caused by autonomic dysfunction, deconditioning, hypovolemia, hyperadrenergic states, and medication effects, with the most common presentation being Postural Orthostatic Tachycardia Syndrome (POTS) in young women. 1

Primary Pathophysiological Mechanisms

1. Autonomic Nervous System Dysfunction

• Partial autonomic neuropathy: Impaired peripheral vasoconstriction leading to venous pooling 2
• Neurogenic orthostatic hypotension: Dysfunction of the autonomic nervous system affecting central or peripheral autonomic nerves 1
• Impaired baroreceptor reflexes: Inadequate compensatory mechanisms upon standing 1

2. Volume-Related Causes

• Hypovolemia: Absolute or relative decrease in blood volume 2
• Dehydration: Inadequate fluid intake or excessive fluid loss 1
• Blood loss: Acute or chronic bleeding 1
• Venous pooling: Excessive blood pooling in lower extremities 1

3. Hyperadrenergic States

• Excessive sympathetic activation: Inappropriate increase in norepinephrine levels 2
• Increased norepinephrine transporter protein activity: More rapid clearance of norepinephrine, reducing vasoconstriction 1
• Immune-mediated processes: Autoantibodies affecting autonomic regulation 3

4. Medication-Induced Causes

• Vasodilators: Cause peripheral vasodilation and reduced venous return 1
• Diuretics: Contribute to volume depletion 1
• Alpha-blockers: Impair peripheral vasoconstriction 1
• Venodilators: Increase venous pooling 1

5. Post-Infectious/Inflammatory

• Recent infections: Particularly viral infections including COVID-19 4
• Immune-mediated processes: Autoantibodies against autonomic nerve fibers 4
• Chronic fatigue syndrome: Often associated with orthostatic intolerance 3

Specific Clinical Syndromes

1. Postural Orthostatic Tachycardia Syndrome (POTS)

POTS is characterized by:

• Heart rate increase ≥30 bpm (or ≥40 bpm in 12-19 year olds) within 10 minutes of standing 1
• Absence of orthostatic hypotension
• Symptoms of orthostatic intolerance (lightheadedness, palpitations, tremor, weakness, blurred vision, fatigue) 1
• More common in young women 5
• Often occurs after a period of inactivity from illness or injury 5
• May follow recent infection or trauma 1

2. Initial Orthostatic Hypotension with Compensatory Tachycardia

• Transient BP decrease within 15 seconds after standing 1
• Transient mismatch between cardiac output and peripheral resistance 1
• More common in young, asthenic subjects 1

3. Classical Orthostatic Hypotension with Compensatory Tachycardia

• Sustained BP decrease within 3 minutes of standing 1
• Preserved or enhanced orthostatic HR increase in non-neurogenic causes 1
• Common in elderly, frail patients 1

4. Delayed Orthostatic Hypotension with Tachycardia

• BP decrease occurring beyond 3 minutes of standing 1
• Progressive fall in venous return and cardiac output 1
• May be followed by reflex syncope 1

Associated Conditions

• Joint hypermobility syndrome/Ehlers-Danlos syndrome 3
• Deconditioning: Physical deconditioning following illness or injury 2
• Parkinsonism: Associated with autonomic dysfunction 1
• Diabetes: Can cause autonomic neuropathy 1
• COVID-19 infection: Emerging cause of POTS-like syndromes 4
• Mast cell activation syndrome: Can contribute to orthostatic intolerance 3

Clinical Pearls and Pitfalls

Key Diagnostic Considerations

• Orthostatic tachycardia without hypotension is the hallmark of POTS, while orthostatic tachycardia with hypotension suggests other forms of orthostatic intolerance 1
• The pattern and timing of BP changes can help differentiate between various causes 1
• Always consider medication effects as they are common contributors to orthostatic symptoms 1

Common Pitfalls

• Overlooking dehydration: Simple volume depletion is a common and treatable cause 1
• Missing medication effects: Many drugs can cause or worsen orthostatic tachycardia 1
• Focusing only on cardiovascular causes: Autonomic neuropathy and deconditioning are common underlying mechanisms 2
• Ignoring post-infectious triggers: Recent infections (including COVID-19) can precipitate orthostatic tachycardia 4

Orthostatic tachycardia represents a final common pathway for multiple overlapping pathophysiologies, and patients often have more than one contributing mechanism simultaneously 3.