What is POTS (Postural Orthostatic Tachycardia Syndrome)? An Explainer
(Stay tuned for additional citations.)
So, what is POTS (Postural Orthostatic Tachycardia Syndrome)? Let’s start by pulling apart the acronym.
Postural means this happens when your body is positioned a certain way. Orthostatic is even more specific: this happens when you are upright (standing, but also, say, legs dangling off a tall bar stool). These two terms are somewhat redundant, and different researchers prefer one or the other. My guess is that they are both included for the purpose of forming an acronym. Sometimes that’s all there is to it.
Tachycardia is a high heart rate.
A syndrome is a collection of signs and symptoms that tend to cluster together. In the case of POTS, it has different causes for different people, and can have multiple causes. Sometimes the cause is unknown. What’s important here is that, while all POTS shares certain key features, everyone’s POTS looks a little different.
So in POTS we have a cluster of signs and symptoms that includes high heart rate on standing/being upright.
What causes that high heart rate? Much of POTS has mechanical causes. When non-POTS people stand, they experience a spike in heart rate as their body compensates for gravity and the change in posture, and then their heart rate normalizes at a slightly higher rate, as their body does what it needs to do to maintain an adequate flow of blood to the head (cerebral perfusion).
But POTS bodies struggle to do this. If you imagine your body as a water balloon dangling from your fingers, this difficulty in getting blood up to the top is most often due to low blood volume (not enough liquid in the balloon) and/or lack of vasoconstriction (not enough squeezing from the bottom of the balloon). The former is referred to as the hypovolemic subtype of POTS. In the latter case, this lack of squeezing of the blood vessels is due to nerve damage in the lower body, so we call this the neuropathic subtype of POTS.
It’s possible to have both of these types at the same time. The end result is that not enough blood (and therefore oxygen) is getting to the brain, so the body panics and the heart revs up to compensate. This is the orthostatic tachycardia part of the POTS acronym. And the heart more or less keeps doing this — it has to — until you sit or lie down. But, the reality is that sitting is still semi-upright, and we only really get rest when we lie down. As a sidenote, anecdotally a lot of us who have had POTS for a while have developed a habit of sitting cross-legged or slouching or with our feet up, because that is more restful for us than sitting up straight.
So we’ve come to the first part of the diagnostic criteria for POTS: in those over 19, a sustained increase in heart rate of 30+ bpm from lying to standing, and in younger people, a sustained increase of 40+ bpm. Unmedicated, I was experiencing heart rates as high as 120 bpm doing meal prep and washing the dishes, while my seated heart rate was in the 70’s or 80’s. Fun times.
Along with this increase in heart rate come other symptoms; remember that the heart is struggling to get enough blood throughout the brain. Many of the symptoms are the sorts of things you might expect if you’re not getting enough blood to your brain: getting lightheaded, dizzy, feeling faint, or actually fainting. Fainting is not a requirement for a POTS diagnosis — as Olshansky et al. state, “Syncope is not a criterion” — but about 30% of people with POTS do sometimes faint. I am not one of them. My POTS mostly manifested as shortness of breath early on; I get less of that symptom now and more lightheadedness when I stand for too long.
There are other possible orthostatic symptoms that aren’t the result of cerebral hypoperfusion, but the key idea is that there are symptoms that are brought on by standing and alleviated by sitting or lying down. This is a second part of the diagnostic criteria for POTS: the presence of orthostatic symptoms. In other words, you don’t need to look at your fitness watch to know something is wrong. Your body already tells you.
There are other POTS symptoms that happen all the time. Here are a few that I experience: fatigue (your heart running a marathon all the time is exhausting), exercise intolerance (duh), brain fog (I hate this one most of all). As POTS is a form of dysautonomia (dysfunction of the autonomic nervous system), it has far-reaching effects on multiple systems.
There are a couple of other things that impact our symptoms that aren’t strictly orthostatic. One is movement. Paradoxically, my heart rate comes down when I walk vs. when I stand. The reason for this is that movement recruits the leg muscles, which act as a second heart, assisting in squeezing the balloon from the bottom and pushing blood back up. A lot of us unconsciously or consciously use this to our advantage when standing: we employ countermaneuvers, squeezing the leg muscles so as to better tolerate standing.
Eating is another thing that can bring on or worsen POTS symptoms, due to splanchnic pooling, which refers to all the blood rushing to your gut to aid digestion. This exacerbates the problem of not enough blood to the head, because that blood is getting sent elsewhere. For this reason, a lot of us experience postprandial symptoms.
Heat is one more thing that can bring on or worsen POTS symptoms, and this includes hot baths and showers (showers especially, as putting your arms up to wash your hair while standing makes it even harder to get blood all the way up!). The main reason for our heat intolerance is that heat causes vasodilation, widening of the blood vessels. This is the opposite of squeezing the balloon from the bottom. Hot weather can also cause dehydration, which reduces blood volume.
But wait, there’s more!
The subtitle of my blog says I have the hyperadrenergic subtype of POTS. That means I get bonus symptoms the other subtypes don’t, at least not at all to the same extent. About 90% of hyperadrenergic POTS cases are secondary to one or both of the other subtypes (hypovolemic and/or neuropathic).
In addition to the necessary compensation for low blood volume and/or lack of vasoconstriction that our hearts do, the bodies of people with hyperadrenergic POTS overreact to the fact of being upright by churning out extra stress hormones.
Everyone who has POTS produces somewhat more norepinephrine, as this is the hormone that revs the heart and squeezes the blood vessels to compensate. But in people with hyperadrenergic POTS, our bodies go a little nuts on the norepinephrine every time we stand. For some small subset of people with hyperadrenergic POTS (the other 10%), their bodies produce extra norepinephrine even at rest.
So, whereas people with the other subtypes of POTS will have a fairly stable blood pressure on standing, ours goes up and doesn’t come down until we sit or lie down. This is one of the ways that the hyperadrenergic subtype of POTS can be distinguished from the others during diagnostic testing. The other is through catecholamine (stress hormone) testing.
(Blood pressure that goes down and stays down during standing is generally indicative of orthostatic hypotension. These are a third and fourth part of the diagnostic criteria for POTS: All other explanations for the high heart rate and symptoms must first be ruled out. Orthostatic hypotension looks so similar to POTS that it gets its own callout in the diagnostic criteria.)
The bigger problem with norepinephrine is that it’s a fight-or-flight hormone: Our bodies respond to standing as if we were being chased by a lion on the savannah. This subtype comes with a ton of physiological arousal: In response to merely standing, we experience sensations that people generally attribute to anxiety. A non-anxiety anxiety is characteristic of POTS — we all tend to experience physiological arousal (bodily anxiety) without cognitive anxiety (worry and anxious thoughts) — but this is particularly pronounced for those of us with the hyperadrenergic subtype. Nowadays I mostly just get wired and maybe a little agitated, as I am on medication, but when it’s worse, I get jittery, clumsy, irritable. I get hypervigilant, don’t like people in my personal space, and experience sensory issues — in short, I feel much like a cornered animal. And, for me, on my worst days, my nervous system seems to blow a fuse and I experience shutdown and collapse, like the traumatic fold response. I call this state “doodlebugging,” as I experience a horribly low mood and just want to curl up into myself.
And this is an important point to end on: These are physiological responses, and POTS is a physiological problem, not a psychiatric one, even though POTS can produce symptoms that seem psychiatric in origin. Many of my peers with POTS have been dismissed as just having anxiety, or “it’s all in your head” despite there being clear signs (the medical term for features that are observable by someone else, unlike symptoms, which can only be self-reported) that there is a malfunction. I myself thought for a time that I might have atypical depression because of my doodlebugging. But I don’t.
Some people with POTS do also have mood disorders like anxiety and depression, or ADHD, and these can certainly interact with POTS symptoms, but they are completely separate diagnoses. You can’t think or therapy or mindfulness or yoga your way out of the mechanical problems of low blood volume or lack of vasoconstriction due to nerve damage or a body that’s being extra with the hormones, apropos of nothing but standing. And, while some people hypothesize our nervous systems can, to some extent, be retrained to not overreact, I haven’t seen any solid evidence of this. At most, it seems like we can work on increasing parasympathetic nervous system activity (think parachute: this is the system that gently brings us down to a “rest and digest” state) and also not adding extra stress on top of our weird bodies being weird.
We have to rely on good habits and a variety of medications to handle the rest. Stay tuned for more on these aspects of POTS management.
