Tilt testing in POTS

Introduction
One of the conditions that I am very interested in is POTS - Postural Orthostatic Tachycardia Syndrome. This is a poorly understood and more importantly, poorly recognised condition which although not dangerous, can make the patient’s life miserable. POTS is characterised by symptoms of orthostatic intolerance - which means that patient’s struggle to maintain an upright posture for a prolonged duration of time because they notice their heart rates shoot up, they feel dizzy, they may get tremulous, they may get breathless and they may even collapse. This is a condition that tends to affect mainly young women (but also men) between the ages of 14-45 years and often patients feel just completely miserable. One of the interesting features of this condition is that it is often associated with a multitude of other symptoms and because doctors are not very aware of this condition, they only do basic tests for the conditions that they do know about and often patients go through a plethora of investigations which are not relevant or useful in confirming the diagnosis of POTS. When these tests come back normal, patients are often unfairly made to feel that they are anxious or even mad and the poor patient can spend several years disabled and debilitated and unsupported and continuously in search of a diagnosis. When i first make the diagnosis in my patients, virtually every patient starts crying because they finally feel believed and validated.
So the most important question is:

How do you make the diagnosis of POTS?
The test that is recommended for a diagnosis of POTS is a passive tilt table test which involves strapping the patient to a table, measuring their heart rate and blood pressure and then tilting the table up vertically and measuring the patients blood pressure and heart rate and as per current definitions, POTS is diagnosed if the patient’s heart rate rises and is maintained at more than 30 beats/minute when they are standing and especially if you are able to reproduce their symptoms.
As tilt table testing is a specialised investigation, it may not be easily accessible and often doctors do what is an active stand test (also called a poor man’s tilt test) where the patient is simply to ask to stand and the doctor measures the heart rate and BP for up to 10 minutes and if the heart rate goes up and is maintained at 30 above baseline then ‘that kind of’ confirms the diagnosis. Whilst both these tests are useful to make the diagnosis, the problem arises when they are negative ie the heart rate doesnt rise by 30 minute. Often these patients are then told that they don’t have POTS and are discharged. The poor patient continues to remain debilitated and is now led to believe that they definitely don’t have POTS and for many of them the endless search continues. The truth is that a negative test does NOT exclude the diagnosis of POTS.
In this video, i wanted to talk about why a negative tilt or active stand test does not exclude the diagnosis.
The first thing to understand is to try and work out what makes for a good investigation. To my mind a good investigation is one which reliably predicts what happens to the patient. This means that before we can be sure of how good a tilt test is what we need to do is to take a bunch of patients with symptoms suggestive of POTS, do a tilt test, divide them into 2 groups - one group who have a positive tilt test and the other group who have a negative tilt test and then treat both groups as if they have POTS and see how any in each group respond to treatment.
If we find that everyone in the abnormal tilt group responds to treatment and everyone in the normal tilt test doesn't then we can say that the tilt is a good investigation but we need that kind of study. Unfortunately that study has not been done. When a condition is defined by a test, we have to first and foremost know how good the test is and we simply don't know this about tilt testing. I have several patients who sounded like they had POTS and had a negative test and still responded very favourably to treatment. This is not just my experience- I was at a conference recently and i asked one of the foremost authorities on POTS in this country and he also told me that up to 50% of his POTS patients responded to treatment despite a negative tilt.
I hope you found this useful.