Introduction

What is postural orthostatic tachycardia syndrome (PoTS)?

PoTS is a condition which causes a sudden increase in heart rate, making you feel dizzy or faint.¹ It is an abnormal response of your body and usually affects you when in an upright or standing position and is usually relieved when lying down.² Unfortunately, the condition is not yet fully understood, and there is currently no cure. Symptoms are usually managed by lifestyle changes or medication. It is believed that the condition is triggered by a bacterial or viral infection, such as COVID-19, pregnancy, surgery or even a traumatic event.³ As the condition shares symptoms with anxiety and dehydration, it can often be misdiagnosed. It is believed the condition is roughly five times more common in those assigned female at birth (AFAB), than assigned male at birth (AMAB), occurring between the ages of 15 and 50 years.² This article focuses on PoTs and the main conditions that are considered as a differential diagnosis to PoTs.

Clinical features of PoTS

The main symptoms you get with PoTS happen in standing position, such as:

• Palpitations (feeling the heart skips a beat)
• Dizziness 
• Lightheadedness
• Chest discomfort or pain
• Claminess or sweating 
• Difficulty breathing
• Near faint episode or fainting 
• Forgetfulness or brain fog
• Stomach related issues, i.e bloating, nausea, diarrhoea or vomiting
• Headaches
• Fatigue
• Trouble with vision

Symptoms can often be triggered by several factors, including:

• Intense exercise or workouts
• Hot environments
• Standing up too quickly 
• After a heavy meal
• Not drinking enough fluids (dehydration)
• Drinking alcohol 
• Those who are AFAB may find that their menstrual cycle can also be a trigger for the condition^2.

Diagnosis

How is PoTs diagnosed?

During your appointment, your GP will take a full medical history, which will involve a series of questions to understand your symptoms. Your GP will arrange specific tests to exclude other similar conditions to PoTs. For an official diagnosis to be made, you will need to be referred to a specialist.²

The GP may conduct a physical examination known as:

Tilt test

• For this examination, you need to lie flat on the examination bed at about 60-70^o and during this, your blood pressure and heart rate will be monitored
• After about 5-20 minutes of lying down, the bed will then be tilted upwards 
• During the exam, the doctor will ask how you feel during the test, so symptoms can be matched with your blood pressure and heart rate
• This can be done for up to 45 minutes, during which your heart rate is constantly measured
• The test ends when your blood pressure becomes either too low, enough information has been obtained, or you have reached the maximum time⁴

The diagnosis should be made if there is an increase of 30 beats per minute within the first 10 minutes of the examination. However, the tilt position can last between 10 - 45 minutes.⁴ 

Prior to the examination, you may be advised to fast for at least 4 hours. This is to ensure you do not vomit whilst being tilted.

Another test which may also be carried out whilst you're with your GP is:

Active stand test

• Similarly to the tilt test, you will lie flat for a few minutes whilst your heart rate and blood pressure are being recorded
• You will then be asked to stand up briefly, and immediately upon standing your heart rate and blood pressure are monitored again 
• This is then continued at frequent intervals for up to 10 minutes.⁴ The test should bring on symptoms of PoTs, and in some cases, people may pass out

Differential diagnosis to consider

It can take some time for you to be diagnosed with PoTS, as the symptoms are quite similar to other conditions. It is often confused with anxiety and dehydration, due to the sudden, rapid heart rate following certain environmental factors and symptoms that are very similar. Anxiety and dehydration can mimic symptoms of PoTs, as they overlap. They all present with dizziness, fatigue and fast heart rates, and due to their similarities can be misdiagnosed. Keeping track of your symptoms and staying well hydrated can help your GP make an accurate diagnosis. Other conditions to consider are:

Hyperthyroidism 

A small gland located in your neck, called the thyroid gland. It releases a hormone responsible for several functions in your body, such as controlling your heart rate, your weight and body temperature.⁵ When the gland starts producing an excess amount of this hormone (T3 and T4), it is known as hyperthyroidism or an overactive thyroid.

Signs and symptoms

Excess levels of thyroid hormones can cause your body to use lots of energy, causing a range of unpleasant symptoms such as.

• Anxiety like symptoms
• Weight loss
• Irritability
• Fast heart rate/palpitations
• Increased fatigue and tiredness
• Sensitivity to heat - sweating
• Swelling of the thyroid gland, which causes a noticeable lump, known as a goitre, to form in the throat⁵

The condition is usually managed fairly well with a group of medications known as thionamides.⁵ They work by controlling and stopping your body from producing too much of the thyroid hormone.

Why is it misdiagnosed? 

Some of these symptoms can often mimic PoTs due to its shared symptoms. For example, the fast heart rate, palpitations, anxiety and sweating. However, unlike PoTS, when investigating the condition, your blood tests will reveal an abnormal thyroid function, and the symptoms do not depend on your posture.

Supraventricular tachycardia (SVT)

A condition where your heart beats too fast, usually above 100 beats per minute, ranging between 150-220 beats per minute. ⁶ This is due to abnormal activity in your heart's rhythm and can last for several minutes, but typically, it only lasts for a minute.⁶ It can occur at any point during the day, even during the resting period. You may not feel symptoms, however, some people can feel many of the symptoms listed below.

Signs and symptoms:

• Palpitations
• Dizziness and lightheadedness
• Tiredness and fatigue
• Chest pain or discomfort 

Symptoms can also often be triggered by caffeine, alcohol, stimulants or sometimes no triggers at all.⁶

The condition is usually treated with medicines to control the episodes of fast heart rates, this is given orally or through a vein (IV). Another method of treatment for SVT is cardioversion – a small electric shock to the heart to help it get back to a normal rhythm.⁶

Why is it misdiagnosed? 

SVT symptoms overlap with PoTs with the sudden episodes of palpitations, dizziness and fast heart rate. Both conditions can also be triggered by alcohol or caffeine. When the symptoms are being assessed, a regular ECG or a 24 ECG may be requested, which will show the abnormal heart rhythm as well as the fast heart rate, excluding PoTs. 

Orthostatic hypotension (Postural hypotension)

A condition in which your blood pressure drops significantly upon standing from a seated or lying position.⁷ This can be caused by various reasons, such as being dehydrated or problems with your heart function, but symptoms subside when you lie down. The chances of developing orthostatic hypotension also increase with age.⁷ During a blood pressure drop, you may start to feel these symptoms.

• Faint
• Dizzy
• Brief loss of consciousness⁷
• Weak 
• Nauseous
• Blurred vision

Treating orthostatic hypotension usually depends on the cause. If caused by dehydration, you will need to increase your fluid intake, and stay hydrated. If caused by problems with your heart function, then medication can be given to help improve this. You may also be advised to stand up slower when getting up from sitting/lying down. Some medications can be given to increase your blood pressure and reduce the effects caused by the condition.

Why is it misdiagnosed? 

Similarly to PoTs, you experience dizziness, feeling faint and lightheaded, and symptoms also improve when you lie down. The key distinction with the condition is that there has to be a significant drop in your blood pressure on standing,>20mmHg on systolic (top number) or >10mmHg on diastolic (bottom number), all within 3 minutes of standing.⁸ Whereas in PoTs, it is defined if there is an increase in heart rate >30 beats per minute without a drop in blood pressure. 

Management

How to manage PoTS

There is currently no cure for PoTs, but management can fall into 2 categories 

1. Non-pharmacological (without medicines) 
2. Pharmacological (using medicines)

Symptoms are usually managed with lifestyle and dietary changes, which may help reduce your symptoms. Some of these changes may include.

• Increasing your daily fluid intake - this will prevent feeling dehydrated
• Taking your time to stand and sit up - reduced chance of blood pressure dropping
• Reducing caffeine and alcohol intake 
• Staying active with low intensity exercises - improves blood flow (although it can trigger symptoms, so seek medical advice)
• Wearing compression stockings and increasing salt intake³

Some people may unfortunately still have symptoms, despite making changes to their lifestyle. Medication can then be offered to help manage your symptoms.

Midodrine - works by narrowing the blood vessels to prevent a sudden drop in blood pressure (used in orthostatic hypotension)

Fludrocortisone - used for retaining salt to increase your blood volume, also used in orthostatic hypotension to prevent low blood pressure.

Some medications known as beta blockers can be used to slow your heart rate down.

Summary

Misdiagnosis of PoTs is unfortunately still quite common, due to the difficulty of fully understanding the cause of the condition. It presents with vague symptoms, making it prone to late diagnosis. The article presents 3 different diagnoses, SVT, Orthostatic hypotension and hyperthyroidism, which share characteristics similar to PoTS. The main difference is that their diagnostic criteria vary. You and your health care professional being able to recognise the differences in each condition is important for accurate diagnosis and management.