How should we measure the “POT” of POTS, and how much does it matter?, 2023, Boris and Fischer

How should we measure the “POT” of POTS, and how much does it matter?

A century and a half ago, a number of Civil War soldiers were noted to develop disabling fatigue with severe orthostatic intolerance after contracting dysentery. They were sometimes labeled as having “Soldier’s Heart” or “Da Costa Syndrome” [2]. Decades later, through careful clinical examination and using a then-new electrocardiograph, Sir Thomas Lewis determined that these soldiers had normal hearts. Lewis labeled the condition “effort syndrome,” and determined that “graduated exercise” was the key to recovery and rehabilitation [1].

In 1972, Streeten and colleagues reported a series of five patients with clinical symptoms and findings similar to those of Lewis’ effort syndrome. Streeten labeled this condition “hyperbradykininism” [3]. The term “postural tachycardia syndrome” was coined for one similar adult woman by Rosen and Cryer in 1982; she improved with increased salt intake [4]. Schondorf and Low labeled the condition “idiopathic postural orthostatic tachycardia syndrome” in a series of adults, suggesting the cause was “a mild form of an acute autonomic neuropathy” [5]. Postural orthostatic tachycardia syndrome (POTS) was later reported in an adolescent in 1999 [6].

Since then, POTS has been identified and characterized in adults and adolescents [7]. The diagnosis depends on a combination of chronic daily symptoms of orthostatic intolerance and excessive postural tachycardia (≥ 40 beats per minute (bpm) change in adolescents, ≥ 30 in adults) [8].

Perhaps prophetically, Lewis’ quotation cited above remains germane. Our current diagnostic labels of what he called “effort syndrome,” are, indeed, potentially nothing more than “temporary conceptions.” Two major issues remain in defining the diagnosis of what we now label as POTS: 1) how should “excessive postural tachycardia” be measured, and, 2) what difference does postural tachycardia make?

https://link.springer.com/article/10.1007/s10286-023-00977-3

 

That is an interesting history.

I have in my study the small wooden cabinet constructed by John Honor, who was chief technical officer to Thomas Lewis, with drawers labelled 'histamine', 'cannulae', syringes' etc.

What I think may be significant is that this group of Civil War soldiers had suffered from dysentery. The nearest thing to ME/CFS I have seen in terms of long term disabling fatigue is Reiter's syndrome, which is a T cell immunological disturbance following intracellular infections and historically dysentery. The relevant organisms are bacteria or what we used to call mycoplasma.

I presume that Lewis was studying British soldiers and they may not have had dysentery though?!

 

DecodeME might just provide clues e.g. infectious trigger (leading to POTs) may be reflected in genetics assessed via DecodeME.

 

There author makes three interesting points about POTS in adolescents.

The threshold for standing test should be lower than for a tilt table test because in the former you're still actively using your leg muscles to stand, promoting venous pumping.

An increase of 40pm in adolescents is not very abnormal. In one study, The 97.5 percentile of HR increase was 41 and 48 bpm, at 2 and 5 min, respectively.

And lastly there is the question if the HR increase is relevant to the symptoms of POTS:

"A large series of adolescents with chronic orthostatic intolerance demonstrated no statistically or clinically significant differences in either symptomatology or symptom burden based on having a 30–39 bpm increase versus a≥40 bpm increase [14]. These data call into question the use of a higher (or any) HR threshold in diagnosing the clinical condition we call POTS. Thus, one could wonder whether the “syndrome” of POTS really should be defined based on a constellation of clinical symptoms rather than largely on the presence or absence of a particular HR change with upright challenge."​

 

Thanks for sharing. It would be interesting to have data on tilt table testing in a large representative sample of the general population to see how well POT correlates with POTS symptoms.

Does anyone know of such as study?

 

Really don't feel I understand this topic but I think the issue is controlling for deconditioning i.e. you'd need controls with very similar lives/activity.

 

Yes that is another big problem. But I meant something differently: a study that does tilt table testing in a representative sample of the general population to see how well POT correlates with OI and other symptoms.

 

Think I've more or less found what I was looking for:
Normal versus abnormal: What normative data tells us about the utility of heart rate in postural tachycardia - PubMed (nih.gov)

The authors did 5 minute tilt table testing in a sample of the general population and found that POT was quite common. The median heart rate increase in young people (18-29 years) was 33 the 95% was 50.9. That indicates that this is very common in healthy people.



The authors write:

"[given...] the lack of any clinically significant orthostatic symptomatology, we would argue that the current hemodynamic values represent normal orthostatic responses, despite meeting the physiological criterion for POTS. [...] We would argue this point further to suggest that even among young healthy adults the current HR increment of 30 bpm is a normal response, warranting reconsideration in age groups beyond pediatric patient populations. Our young adult population (18–29 years) attained an average HR response of 33.7 bpm on HUT, with ΔHR's > 40 bpm for individuals in the 95th percentile. So why is this important? The age range for most POTS patients is 15–40 years (Low et al., 2008). Given the high propensity for young healthy adults to express higher HR increments on orthostatic challenges, it is reasonable to question whether younger individuals who present with, arguably a normal HR response, along with some constitutional symptoms such as generalized lightheadedness, dizziness, fatigue, etc. that aren't appropriately interpreted, may be over diagnosed with POTS."​

 

That suggests that the tilt table test is of pretty little value as far as I can see.

 

The laboratory cabinet used by Thomas Lewis when discovering the Triple Response due to histamine release.

 

There are more of these. Plan to write a blog post about it to summarize the main findings. Might have important implications for POTS and OI research in ME/CFS.

 

That's a very interesting study. Very quick skim: Reasonable sample size (n=252). ΔHR regressed significantly with age in females but not males; younger individuals showed larger increments during head-up tilt compared to older individuals. Young adults (18-29 group) had an median ΔHR of 33.7 bpm which is just above the POTS threshold. Statistically significant findings for most analyses & appropriate correction for multiple comparisons.

A non-age/sex-adjusted ΔHR of 30 bpm for diagnosing POTS seems unsustainable, although the significant weakness is the use of a 5-minute tilt (which the authors do acknowledge). They say 10 minutes is usual but I remember mine was significantly longer - I think it was 30m.

Also recruiting from "activity centres" may result in more physically active participants.