Ask the Expert monthly column
If you or a loved one has experienced a fainting episode, you’re not alone. The goal of the Take Fainting to Heart campaign is to provide relevant information and innovative educational resources to help you understand the seriousness of fainting and the importance of visiting a doctor to determine if it is caused by an underlying, serious health problem.
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February: What causes POTS?
Q: “What causes POTS? I thought it was related to an autonomic dysfunction but I suffered a viral infection some months ago and my doctor thinks the two may be connected.”
A: Great question. POTS, or Postural Tachycardia Syndrome, is probably a collection of problems characterized by an intolerance to upright posture. Typically after a few minutes upright people with POTS become lightheaded and have palpitations with an increase in heart rate above 120 bpm. Often they become tremulousness, and some people have a variety of gastrointestinal (stomach/abdominal) symptoms too. All of this can be quite distressing.
Let’s start with the palpitations and increased heart rate. Heart rate is governed by two very old parts of the nervous and hormone systems. One part releases a chemical called acetylcholine, which slows down the heart rate. The other part releases chemicals called catecholamines, which raise heart rate, increase how strongly the heart squeezes with each beat, and can regulate blood pressure. The two interact, so when you are lying down acetylcholine dominates over catecholamines, and your heart rate goes down. Usually the two are finely balanced, so that all parts of your body get the right amount of blood flow as you move through the day.
The problem with POTS is that catecholamines seem to rise higher than normal when you are upright. There are several possible reasons why this happens. One reason is that another one of your hormone systems fails to respond appropriately to changes in blood volume and catecholamines have to take over. Another possible reason is that some of the tiny nerves that regulate your blood pressure are damaged, and once again catecholamines step in to fill the breach. A third possible cause is that catecholamines increase more than they should when you are upright.
What does this have to do with POTS? Catecholamines increase your heart rate, and each heart beat is a bit harder than usual. This gives an uncomfortable but not dangerous sensation of palpitations. Additionally, high catecholamine levels can cause a very fine tremor (shaking). This is the reason for palpitations, increased heart rate and shakiness when you are upright.
Having said that, there is very little evidence that virus infections cause POTS. It is an interesting idea but there are no good scientific papers about this.
Dr. Robert S. Sheldon
Professor of Cardiac Sciences, Medicine and Medical Genetics
University of Calgary Vice President Research, Calgary Health Region
Download archive Ask the Expert monthly column
January Column: Dr B Grubb and B Karabin on Reflex Syncope
December Column: Prof R Sutton on Diagnostic Tests
November Column: Dr N Tullo on Fainting
