Differential Diagnosis of OI  with Excessive Upright 

tachycardia ‐

a Physiological Response to Central 

Hypovolemia?

Normal Circulatory Response to Orthostasis

Normal Segmental Changes in Normal Segmental Changes in Impedance and volume with TiltImpedance and volume with Tilt

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Thorax Splanchnic Pelvic Leg

Orthostatic IntoleranceThe presence of one or more symptoms, e. g., lightheadedness, dizziness, nausea, breathlessness, and vision change, linked specifically to assuming or maintaining upright posture, and symptoms abate once supineEtiology is not a criterion.

Chronic Orthostatic IntoleranceOrthostatic Intolerance for at least 3 months with functional impairment

POTSChronic Orthostatic Intolerance with excessive postural tachycardia (at least 40 bpm change within 10 minutes on standardized passive tilt testing) without significant sustained hypotension in the absence of an alternative explanation.If a specific cause is found (e.g. Addison’s Disease) It is no longer called POTS. But the POTS Response is still present.

POTS is a Disease vs POTS is a Physiological Response

Major Variants of Orthostatic Intolerance Comprise a Differential Dx of POTS

•Chronic Bedrest

•Initial Orthostatic Hypotension

•Orthostatic Hypotension

•Chronic Orthostatic Intolerance Postural Tachycardia Syndrome (POTS) Chronic OI

•Postural Vasovagal Syncope/I.S.T.

•Any Condition that Promotes Central Hypovolemia

Gravitational Deconditioning

• Reduced blood volume• Cardiovascular remodeling• Different Regional blood volume redistribution• Reduction in the response to

norepinephrine/MSNA (and other pressors)

Initial Orthostatic Hypotension

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Standing

Orthostatic Hypotension (OH) is Easy to Understand

•Blood pressure falls sufficiently to impair brain blood flow

•Non-neurogenic OH• Hypovolemia or Forced Vasodilation

•Neurogenic OH •Autonomic vasoconstrictor failuredue to inadequate release of norepinephrine from sympathetic vasomotor neurons.

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Chronic Orthostatic Intolerance: Postural Tachycardia Syndrome (POTS)

Schondorf and Low. Idiopathic postural orthostatic tachycardia syndrome: an attenuated form of acute pandysautonomia? Neurology 1995;43:132-137

Day-to-Day Symptoms of OI++

Excessive Tachycardia(without Hypotension)Adults Δ>30 or HR>120bpm within 10minAdolescent – Δ>43

(IOH a confound)?+

Concurrent Symptoms of OIduring testing

Improved by Recumbence

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What’s This?

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Postural Vasovagal Syncope in the YoungDefined by Clinical History

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Tilt Up Tilt Down

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MAPSlow ↓

BP

Rapid ↓

BP

1 2 3Transient loss of consciousness and postural tone due to global cerebral hypoperfusion and characterized by rapid onset, short duration, and spontaneous recovery.

Almost always the result of systemic hypotension

Very Common (~40%)