What Is POTS?
The Postural Tachycardia Syndrome, or “POTS,” is a condition that was first described many decades ago, but many people have never heard of it. It remains relatively misunderstood in most medical circles. Patients with POTS are often misdiagnosed as having “chronic fatigue syndrome,” panic attacks or anxiety, cardiac arrhythmias, or some other malady. POTS results in a what is known as “orthostatic intolerance,” with the word orthostatic referring to being upright. That means that patients with POTS feel much better lying down than when they are sitting or standing. The most common symptoms of POTS include a sense of a rapid heart beat, lightheadedness, fatigue, exercise intolerance, and decreased concentration (also known as "brain fog"). Other symptoms may include headaches, gastrointestinal problems like abdominal bloating or pain, nausea, diarrhea or constipation, chest discomfort, and occasionally fainting, though fainting generally occurs due to a drop in blood pressure. These symptoms may occur immediately upon standing or sometimes occur after the patient has been standing for a few minutes.
POTS affects mostly women, and can begin from teenage years up to middle age. Symptoms can be severe enough to interfere with normal everyday activities, and younger patients can be severely debilitated such that they cannot attend school. POTS can affect anyone, and well-conditioned athletes may suddenly find themselves unable to get out of bed without feeling awful. The most common way of diagnosing POTS in patients with these symptoms is by demonstrating an increase of heart rate of at least 30 beats per minute (or having the heart rate exceed 120 beats per minute) within 10 minutes of standing up. So if your resting pulse runs 70 beats per minute (bpm) lying down but increases to 105 bpm when you stand up, you may have POTS. Generally, the blood pressure stays the same or may even increase slightly. It is important to understand that POTS is a syndrome, not a disease. The difference is that is disease is generally caused by one particular problem, but POTS may occur due to any number of different physiologic disturbances. POTS physician-specialists are most successful when they try to determine the exact cause of the disturbance, since that helps them formulate a treatment strategy that is most likely to be effective.
The Physiology of Standing Up
One of the most important functions of the autonomic nervous system is to compensate for gravitational forces. Gravity has an important effect on the distribution of blood throughout our body. Our blood literally sloshes around the inside of our cardiovascular system because the veins in our arms, legs, abdomen and pelvis are able to stretch and expand significantly, and when anyone stands up about one-third of our blood volume is dragged into the bottom half of our body by gravitational forces. As the blood shifts downwards, away from our heart, the amount of blood reaching the heart is reduced. Since the heart can only pump what blood it receives, this decrease in "venous return" has the effect of reducing the amount of blood that the heart can pump (reduced cardiac output). This results in a slight drop in blood pressure and reduced blood flow to the brain. The autonomic nervous system can sense this downward shift of blood since it receives information from nerve endings in the walls of the veins that relay how much the vein is being distended, and also receives information from the pressure sensors in the carotid arteries leading to the brain to let the brain know that the blood pressure has dropped. The autonomic nervous system immediately responds by increasing sympathetic tone, and the adrenaline that is released by those nerve endings result in constriction of blood vessels to raise the blood pressure. The increased sympathetic tone also causes the heart rate to increase, usually by 5 or 10 beats per minute (up to 20 beats per minute is still considered "normal") to compensate for any drop in blood pressure.
POTS patients are unable to compensate properly for gravity. Gravity becomes their "kryptonite," and standing up becomes a challenge. What often happens is that the reduction in cardiac output causes a normal increase in sympathetic tone, but either the blood vessels don't constrict properly or there is excessive venous pooling, resulting in a marked decrease in venous return such that the heart cannot pump adequately. At that point, the autonomic nervous system has no choice but to increase the heart rate dramatically (usually by 30 beats per minute or more) in order to maintain a normal blood pressure, but the combination of a rapid heart rate and decreased cardiac output leads to most of the symptoms of POTS.
Neurogenic POTS
Specialists who treat POTS recognize that it comes in different forms. The most common variety affects patients fairly suddenly, often after a viral illness like COVID or influenza. It can even occur after an injury like a concussion, a motor vehicle accident, or after surgery. It is known as the “neurogenic” POTS. The exact cause is not entirely understood, but there is mounting evidence that it may be due to an “autoimmune” process, whereby antibodies triggered by the infection or injury may attack the patient’s own nervous system, specifically affecting the autonomic nervous signals that control the blood vessels. As a result, the blood vessels are unable to constrict adequately to compensate for the gravitational shift in blood that occurs with sitting up and standing, and as a result there seems to be an excessive amount of pooling of blood in the legs when the patient stands up for more than a few minutes. Often patients will notice that their hands and legs will turn dark blue after standing for a couple of minutes, such as in the shower. Without an effective means of getting the blood to go uphill from the legs to the heart, the heart cannot pump sufficient blood to meet the body’s needs. The brain responds by increasing the heart rate to compensate for a low blood flow state. However, this increase in heart rate is not enough, so patients feel fatigued and often lightheaded, together with a sense of a racing heartbeat. The diagnosis of POTS can be made with a history and physical examination (with measurement of blood pressure and heart rate while lying, sitting, and standing). Formal Tilt Table Testing is not recommended unless the diagnosis is uncertain even after a thorough history and physical exam.
Hyperadrenergic POTS
A second, less common, form of POTS is the “hyperadrenergic” form. That name implies an overall increased sympathetic tone with an excessive amount of adrenaline. These patients tend to have more complaints of palpitations, tremors, sweating, and headaches. Their heart rate lying down is often faster than the neurogenic POTS patients, and usually the blood pressure increases significantly when they stand up. The age of onset is often younger, and the symptoms begin gradually, not suddenly like neurogenic POTS patients. This can be suspected by careful vital sign measurements on physical exam, but it can be confirmed with Tilt Table Testing together with measuring the level of adrenaline in the blood while the patient is standing.
Joint Hypermobility and POTS
There are certain medical conditions that are commonly seen in POTS patients. One is known as joint hypermobility, meaning that many of the joints (like elbows, knees, and wrists) extend farther than normal. People used to call this condition being "double-jointed." There are differing degrees of hypermobility, but the most severe is a form of the genetic condition known as Ehlers-Danlos Syndrome or EDS. EDS comes in many different forms. It is an inherited disturbance in the body's ability to form collagen, the protein found in most of our fibrous tissues like skin, joints and ligaments. If the collagen forms incorrectly, it winds up being too "stretchy," then the joints can be looser than they should be, which can sometimes lead to injuries. This is known as "Type 3 EDS." Other forms of EDS can make the skin very stretchy and rarely can even affect blood vessels. Since collagen is found in high concentration in the walls of the veins, Hypermobile EDS can result in excessive venous pooling and may lead to POTS. Some patients have a milder form of joint hypermobility. They don't meet all the diagnostic criteria for EDS, so they are sometimes labeled as having the "joint hypermobility spectrum disorder" or HSD.
One of the most important treatments of POTS and joint hypermobility is exercise. Exercise helps strengthen and stabilize the joints in order to reduce the risk of injury. Exercise also helps something we call the "skeletal muscle pump." This concept refers to the fact that the veins in the legs lie between the muscles, and when the leg muscles contract they squeeze on the veins, producing a force that helps the blood flow upward back towards the heart. Leg strengthening exercises (with resistance, to build up the muscles) will help reduce the venous pooling and can reduce the symptoms of POTS. Compression undergarments are another helpful intervention, but only thigh-high hosiery or abdominal/pelvic compression (like "slimware") are generally considered effective. Knee-high hosiery usually won't help much.
Mast Cells and POTS
In the last five years or so a new clinical disorder has been described. The disorder is called a "Mast Cell Activation Disorder" or MCAD. MCAD is frequently seen in POTS patients, often in association with joint hypermobility, and the three together are considered the "Triple Threat" in patients with severe dysautonomia.
Mast cells are specialized white blood cells that are part of our immune system. Think of them as being the "first line of defense" against foreign proteins. They are found in the skin, the upper and lower airways, and throughout the gastrointestinal tract. The most common syndrome that mast cells cause is "hay fever," which is the allergic reaction that occurs when someone inhales pollen. Pollen contains proteins that "activate" the mast cells by interacting with protein receptors on the surface of the cell. The result is that the mast cell releases a substance called histamine, which is potent chemical that causes localized inflammation, leaking of capillaries, and activation of other chemical substances that result in the symptoms of nasal congestion, runny nose, and itching. If the mast cells misbehave for one reason or another, they may release histamine inappropriately. This can cause a variety of symptoms including red blotchy rashes or hives, shortness of breath, nausea, abdominal pain or bloating, diarrhea, constipation, and brain symptoms like fatigue, lightheadedness and brain fog. The list of symptoms of MCAD is long and affects virtually every organ system.
There is no good test for MCAD, though sometimes the serum tryptase level may be elevated on a blood test, or sometimes the urinary levels of histamine may be high, but those tests are not always reliable. Often, starting antihistamine therapy will result in significant reduction in symptoms, and this is indirect proof that the patient may be suffering from this disorder. MCAD tends to run in families, and so there may be a genetic predisposition to having this condition.
Secondary POTS
Certain diseases can cause POTS, and in that case we refer to it as "Secondary" POTS. These diseases include diabetes, sarcoidosis, amyloidosis, Sjogren’s Syndrome (mixed connective tissue disease), and lupus. Sometimes POTS may be an early sign of a more diffuse form of autonomic failure such as pure autonomic failure or multiple systems atrophy, or may be a sign of underlying cancer. However, secondary POTS tends to occur in older individuals. Young patients who present with symptoms of POTS usually fit in one of the categories described above.
Treatment of POTS
The treatment of POTS should always be individualized, depending on the type of POTS, the age of onset, the severity, and the duration of the symptoms. The first steps include drinking plenty of water and eating a high salt diet, as that can correct any blood volume deficiency that can lead to a low cardiac output. Certain exercises can be helpful, including aerobic exercise in a sitting position (using a recumbant bicycle or rowing machine is optimal) and leg-strengthening exercises to improve the circulation and enhance the skeletal muscle pump. Swimming is a particularly good exercise in POTS, because the pressure of the water helps keep the blood from pooling in the lower parts of the body. There are a variety of medications that can be helpful as well. It is highly recommended that you see a physician who specializes in the treatment of POTS and dysautonomia, since most physicians do not have sufficient experience to evaluate the optimal treatment strategy for all POTS patients. Luckily, there is a good chance most young patients with POTS will improve over time, though it may take years. In the meantime, patients often benefit from medical therapy in order to be able to work or go to school without intolerable symptoms.