Causes and Classification

Events that trigger PoTS

PoTS has been reported to have commenced after:

• An infection such as a bacterial or viral infection (including COVID -19)
• A life stressor such as pregnancy or surgery
• A traumatic event
• Immunisation

However, the exact link with some potential triggers remains unclear.

Canadian Classification of PoTS and related disorders

This is a suggested classification for PoTS which is currently used by some UK specialists.

*Orthostatic intolerance means symptoms that develop when upright and are relieved by lying down.  

PoTS

Definition, diagnostic criteria and symptoms are described elsewhere on our website.

PoTS Plus

As well as meeting the diagnostic and symptom criteria for PoTS, these patients will also have at least one of the following associated symptoms:

• Gastric emptying problems (food passes more slowly from the stomach through the gut)
• Vomiting
• Constipation
• Neurogenic bladder (problem with the nervous system which causes problems passing urine)
• Severe chronic pain
• Headaches
• Significant flushing
• Severe allergic reactions
• Severe food intolerances

PoTS Plus – other conditions which may exist alongside PoTS

• Chronic migraine/cerebrospinal fluid leak
• Hypermobile Ehlers-Danlos syndrome and hypermobile spectrum disorder
• Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)
• Fibromyalgia
• Autoimmune disorders e.g.
  • Hashimoto’s thyroiditis (The immune system attacks the thyroid gland, making it swell and become damaged.)
  • Sjogren’s syndrome (causing dry eyes, mouth and skin amongst other symptoms)
  • Rheumatoid arthritis (causing joint pain and swelling)
  • Lupus (may cause a skin rash, joint pain and swelling and tiredness)
• Mast cell activation disorder
• Coeliac disease (intolerance to gluten)
• Mitochondrial Disease (Mitochondria produce energy in cells but become ineffective in doing so in mitochondrial disease.)
• Multiple sclerosis
• Since the Canadian classification, an association has been made between neurodiversity, hypermobility and autonomic dysfunction.

PoTS Symptoms without Tachycardia (PSWT)

Meets the symptom criteria for PoTS, and therefore has symptoms of orthostatic intolerance (see symptoms of PoTS which occur on standing), but does not have tachycardia on standing.   

Postural Tachycardia of other cause (PTOC)

Meets the diagnostic criteria for PoTS, but a reversible cause can be identified, therefore a PoTS diagnosis should not be given.

• Dehydration or blood loss
• Hormonal
• Anaemia (low iron)
• Anxiety and panic attacks
• Medication side effects
• Recreational drugs
• Prolonged or sustained bed rest (deconditioning)

Inappropriate Sinus Tachycardia (IST)

IST is defined as a heart rate of greater than 100 beats per minute with an average heart rate over 24 hours of over 90 beats per minute, causing palpitations, with no other identifiable cause.

There is an exaggerated heart rate response to exertion, postural changes and emotions, with the heart rate taking longer to recover.

The symptoms of those with PoTS and IST are similar but in IST the trigger is often physical and emotional stress, whereas the fast heart rate in PoTS tends to be caused by being upright. Tachycardia may occur at night while lying down with IST.

The two conditions can overlap and may share the same underlying causes.

Treatment may be with beta-blockers or ivabradine to slow down the heart rate.

Subtypes

PoTS has been divided up into different types of PoTS according to the mechanism within the body that causes symptoms. There is overlap, and therefore these different subtypes can occur in the same person at the same time.  

Neuropathic PoTS

The nerves that serve the autonomic nervous system in the hands and feet do not work properly resulting in widening of blood vessels and tachycardia. 50% of people may experience pooling of blood in the stomach, pelvis, hands and feet (PoTS feet/acrocyanosis). 

There may also be loss of sweating in the lower limbs.

Deconditioning is common.

Blood tests to check for autoimmunity may be abnormal in neuropathic PoTS.

Hypovolemic PoTS (reduced blood volume/dehydration)

30% of patients have low levels of sodium expelled in the urine (<170 mmol per 24 hours) which may indicate a low blood volume.

Hypovolemia can occur as part of PoTS but can also occur as a result of gut problems such as diarrhoea, feeling sick and vomiting. This can cause a further worsening of symptoms.

Hyperadrenergic PoTS

Between 30-60% of patients may have high levels of blood norepinephrine levels on standing and a high or fluctuating blood pressure.

When upright, individuals may experience palpitations, a sense of anxiety, tremor, and cold sweaty hands and feet. Also, in a good proportion of individuals, there is a significant urge to pass urine after even a short period of time upright.

Symptoms may worsen with physical and emotional stress.

Hyperadrenergic PoTS can occur as a result of both hypovolaemia and neuropathic PoTS.

Norepinephrine Transporter (NET) Deficiency is suggested as one rare mechanism for hyperadrenergic type PoTS. There may be an abnormality in a gene that leads to too much norepinephrine circulating in the body.

Deconditioning

Deconditioning (being out of shape) is present in some individuals with PoTS. A traumatic event or illness can result in reduced activity or bedrest. Patients become unfit and the heart doesn’t pump as efficiently as before. This can trigger symptoms of orthostatic intolerance, so patients avoid exercise, which makes their symptoms worse, leading to more physical inactivity. There is a downward spiral of deconditioning which can worsen symptoms of PoTS.   

66% of those in a survey of UK PoTS patients were physically active at the time of onset of PoTS and it is unclear to what degree deconditioning is cause or effect.