Introduction 

What is postural orthostatic tachycardia syndrome?

Postural orthostatic tachycardia syndrome, otherwise referred to as POTS, is a long-term health condition in which your autonomic nervous system does not work properly. This part of the body governs processes we don’t control or think about, such as heart rate, digestion, and sweating. This is why POTS causes symptoms including tachycardia, nausea, abdominal pain, and heat intolerance. 

Orthostatic intolerance

In addition to these widespread symptoms, POTS is typically associated with orthostatic intolerance. This is an inability to maintain an upright posture, which can cause dizziness.

In the normal functioning of the autonomic nervous system, blood vessels tighten and heart rate increases slightly when you assume an upright posture to supply blood to the brain.  

If you have POTS, the coordination between the narrowing of blood vessels and heart rate change is off balance. When sitting or standing up, blood vessels do not sufficiently constrict and blood pools at the feet instead. This causes you to feel dizzy because there is insufficient blood supply to the brain. To compensate for this loss, the heart rate will significantly increase in an attempt to send blood to the brain, causing you to experience a pounding sensation in your chest. 

Importance of early diagnosis

A timely diagnosis is rarely achieved in POTS. A report from Dysautonomia International found that it takes nearly 6 years for the average person presenting with POTS symptoms to receive a diagnosis. Reasons for this include a similar clinical overlap between POTS and other health conditions which prevents an accurate diagnosis from being made, as well as a poor understanding of its symptoms and causes.

Therefore, greater awareness of POTS is needed so healthcare professionals can recognise suspected cases of the condition, allowing you to receive prompt treatment that will enable you to have as good a quality of life as possible and reduce possible complications.

Diagnosis of POTS

Clinical evaluation

This primarily involves considering your medical history. Your doctor will likely ask you questions based on the following factors:

• Any significant event (i.e., surgery, trauma, viral illness) that preceded the onset of your symptoms – this may help to ascertain the cause of your POTS
• Triggers that worsen your symptoms – many patients report a hot environment, exercise and carbohydrate-heavy meals as examples of these
• The severity of your symptoms and to what extent they impact your quality of life
• Any medications you currently take – some are known to have POTS-related side effects

As part of the diagnostic process, you may undergo a physical examination. This will include measuring your heart rate and blood pressure to see how these observations change between lying down and standing up. Joint hypermobility is common in POTS and the Beighton Scoring System helps to assess how flexible your joints are.^1,2

Diagnostic criteria

For a diagnosis of POTS to be made, you must fulfil all of the following criteria:^1,2

1. Sustained heart rate increase of 30 beats per minute or more within 10 minutes of assuming an upright posture – if you are aged 12-19 years your heart rate should increase by 40 beats per minute or more
2. No orthostatic hypotension – systolic blood pressure should not fall by 20mmHg or more
3. Symptoms are persistent, worse while upright and are often relieved upon lying down, for example, lightheadedness, palpitations, tremulousness, generalised weakness, blurred vision, and fatigue
4. Symptoms should have persisted for 3 months or more
5. Other conditions associated with tachycardia should be ruled out – for example, anaemia, severe anxiety, and acute hypovolemia due to dehydration or blood loss

Additional testing

Autonomic function testing, including the head-up tilt table test, is considered the ‘golden standard’ in diagnosing POTS. During this procedure, you lie on an examination couch with safety straps and a footrest to stop you from sliding off. You will slowly move from lying to an upright position, and your heart rate and blood pressure will be monitored during this time to see how you respond to the change in posture. The head-up tilt table test has high diagnostic sensitivity, meaning it can accurately identify cases of POTS.¹

A 12-lead electrocardiogram, or ECG, is a test that measures your heart’s activity through the placement of electrodes on the chest. Holter monitoring is a portable version of this test and involves wearing a small device attached to the waist for up to 7 days. The advantage of Holter monitors compared to a standard ECG is that they can detect changes in your heart’s activity over a prolonged period. This makes it more representative of how your heart responds to different daily activities. 

Your doctor may order an echocardiogram, a type of ultrasound scan that examines the structure of your heart. There is a common misbelief that POTS is a heart condition, but instead, it affects your autonomic nervous system, meaning patients with POTS usually have a structurally normal heart. Therefore, echocardiography is useful for excluding other heart-related disorders that can resemble POTS.³

Exclusion of disorders with similar clinical overlap

POTS is similar to many other medical conditions, and a diagnosis is often made after ruling out these disorders. Such examples include:

• Anaemia
• Electrolyte disorders
• Thyroid disease
• Adrenal hormone abnormalities

A simple blood test can help with this exclusion process. For example, measuring your haemoglobin and thyroid-stimulating hormone levels can indicate if you are anaemic or have thyroid disease, respectively.^1,3 

Challenges in diagnosis

As mentioned previously, the key barrier to getting a POTS diagnosis is that the condition closely resembles a plethora of other medical issues. POTS is often confirmed when all other possible explanations for your symptoms have been excluded, hence why diagnosing the condition is such a lengthy process.

Another important issue is a lack of awareness of POTS, even in doctors who specialise in managing conditions related to the heart. New methods need to be implemented so that doctors are familiar with the condition and its current treatment options. The ‘grassroots approach’ has been suggested, in which you, as a patient, help to educate doctors so that you can learn about POTS collectively. Once the condition starts to become more integrated into medical practice, it is hoped that doctors will scale up this knowledge to help future patients.⁴ 

FAQs

What happens if I have symptoms of POTS but don’t entirely fulfil the diagnostic criteria?

POTS symptoms greatly overlap with other medical problems so your doctor may consider an alternative diagnosis if your symptoms are more consistent with another condition. This could include other failures of the autonomic nervous system, such as inappropriate sinus tachycardia and baroreflex failure. 

Are the diagnostic procedures painful?

The tests used for the diagnosis of POTS are largely painless. The healthcare professional performing the procedure will ensure you are comfortable throughout. During an ECG, you may feel some minor discomfort upon removal of the electrodes from the chest but this is generally temporary. The gel applied to the chest during an echocardiogram is occasionally reported as unpleasant due to the cold sensation it causes. However, this is short-lived and you will be able to rinse the gel off after the procedure.

What happens after I’ve been diagnosed with POTS?

Once you have been diagnosed with POTS, a comprehensive treatment plan should be discussed, to try various treatment methods until you find the regimen that is most effective at controlling your symptoms. 

Summary

POTS is an autonomic nervous system disorder that can cause you to experience many symptoms, namely a fast heart rate and dizziness. There is a set of criteria that guides doctors in the diagnosis of POTS and other approaches are often used alongside this, including a clinical evaluation, head-up tilt table testing, ECG, and echocardiography. POTS closely resembles many other medical conditions so diagnosis is based on ruling these out. Poor clinician awareness delays the time it can take for you to receive a diagnosis so an improved understanding of POTS is needed.