Investigations
1st investigations to order
ECG
FBC
Test
Order FBC to exclude anaemia as a potential cause of orthostatic tachycardia.[1][4] See Assessment of anaemia.
Result
normal
thyroid function tests
Test
Order thyroid function tests (thyroid-stimulating hormone, free thyroxine, free triiodothyronine) to exclude hyperthyroidism as a differential diagnosis.[1][4] See Graves' disease.
Result
normal
electrolytes
morning serum cortisol
Test
Order morning serum cortisol level to exclude primary adrenal insufficiency (Addison's disease) as a differential diagnosis.[4][44] See Primary adrenal insufficiency.
Result
normal
Investigations to consider
Holter monitor
Test
Consider a 24-hour Holter monitor, which can help confirm the diagnosis by demonstrating the association between tachycardia and orthostatic changes.[2] A Holter monitor can also rule out supraventricular arrhythmias that may have a similar presentation to POTS.[2]
Result
tachycardia induced by orthostatic changes; no supraventricular arrhythmias[2]
echocardiogram
tilt-table test
Test
Organise a tilt-table test if the patient is unable to perform a 10-minute standing test, or if the diagnosis is unclear after the initial assessment of orthostatic blood pressure and heart rate and you have a high suspicion of POTS.[1][2] If the diagnosis is unclear, a tilt-table test is helpful because it will provide an assessment of vital signs over a greater time period compared with a simple 10-minute standing test.
Result
orthostatic tachycardia with changing position
supine and upright plasma adrenaline and noradrenaline levels
Test
If the patient’s symptoms do not resolve or significantly improve, consider referral to a centre experienced with the autonomic testing of POTS, where available, to organise further investigation of the underlying pathology.[2] This includes supine and upright plasma adrenaline and noradrenaline levels, which should be considered if hyperadrenergic POTS is suspected.[43] However, this should not be performed routinely because the significance for patient management and outcome is unclear.[2]
thermoregulatory sweat test
Test
If the patient’s symptoms do not resolve or significantly improve, consider referral to a centre experienced with the autonomic testing of POTS, where available, to organise further investigation of the underlying pathology.[2] This includes a thermoregulatory sweat test, which should be considered to detect the autonomic neuropathy associated with POTS.[2] However, this should not be performed routinely because the significance for patient management and outcome is unclear.[2]
Result
abnormal patterns of body sweating
quantitative sudomotor axon reflex test
Test
If the patient’s symptoms do not resolve or significantly improve, consider referral to a centre experienced with the autonomic testing of POTS, where available, to organise further investigation of the underlying pathology.[2] This includes a quantitative sudomotor axon reflex test if neuropathic POTS is suspected.[42] Neuropathic POTS is associated with peripheral venous pooling and reduced effective intravascular volume, which is caused by peripheral sympathetic denervation.[1][2] However, quantitative sudomotor axon reflex test should not be performed routinely because the significance for patient management and outcome is unclear.[2]
Result
abnormal post-ganglionic sympathetic sudomotor function[42]
Valsalva manoeuvre
Test
If the patient’s symptoms do not resolve or significantly improve, consider referral to a centre experienced with the autonomic testing of POTS,where available, to organise further investigation of the underlying pathology.[2] This includes the Valsalva manoeuvre with haemodynamic monitoring, which can detect autonomic dysfunction.[2][4] However, this should not be performed routinely because the significance for patient management and outcome is unclear.[2]
Result
excessive increase in blood pressure at the end of the manoeuvre if the patient has hyperadrenergic POTS[4]
deep breathing test
Test
If the patient’s symptoms do not resolve or significantly improve, consider referral to a centre experienced with the autonomic testing of POTS, where available, to organise further investigation of the underlying pathology.[2] This includes the deep breathing test with haemodynamic monitoring, which can detect autonomic dysfunction.[4] However, this should not be performed routinely because the significance for patient management and outcome is unclear.[2]
Result
preserved vagal function is often found in POTS, demonstrated by the sinus arrhythmia ratio in response to deep breathing[4]
exercise testing
Test
Formal cardiopulmonary exercise testing can be useful as a measure of exercise capacity, which is often reduced in patients with POTS.
Result
exercise capacity baseline; often reduced in patients with POTS
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