| Autonomic dysfunction | |
|---|---|
| Classification and external resources | |
| ICD-10 | i |
| ICD-9 | 337.9 |
| MeSH | D054972 |
Postural orthostatic tachycardia syndrome (POTS, also postural tachycardia syndrome) is a condition of dysautonomia,[1] more specifically orthostatic intolerance, in which a change from the supine position to an upright position causes an abnormally large increase in heart rate, called tachycardia. Several studies show a decrease in cerebral blood flow with systolic and diastolic cerebral blood flow (CBF) velocity decreased 44% and 60%, respectively.[2] Patients with POTS have problems maintaining homeostasis when changing position, i.e. moving from one chair to another or reaching above their heads. Many patients also experience symptoms when stationary or even while lying down.
Symptoms present in various degrees of severity depending on the patient. POTS can be severely debilitating. Some patients are unable to attend school or work, and especially severe cases can completely incapacitate the patient.
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The hallmark symptom of POTS is an increase in heart rate from the supine to upright position of more than 30 beats per minute or to a heart rate greater than 120 beats per minute within 12 minutes of head-up tilt.
This tachycardic response is sometimes accompanied by a decrease in blood pressure and a wide variety of symptoms associated with hypotension. Low blood pressure of any kind may promote the following:[3]
Chronic or acute hypoperfusion of tissues and organs in the upper parts of the body are thought to cause the following symptoms:
Autonomic dysfunction is thought to cause additional gastrointestinal symptoms:
Cerebral hypoperfusion, when present, can cause cognitive and emotive difficulties. Symptoms that persist in the supine (recumbent) state are difficult to attribute to "cerebral hypoperfusion"
Inappropriate levels of epinephrine and norepinephrine lead to anxiety-like symptoms:
Symptoms of POTS overlap considerably with those of generalized anxiety disorder, and a misdiagnosis of an anxiety disorder is not uncommon.
Prolonged inactivity of any cause, especially when much time is being spent in the supine (recumbent) position, will lead to a diminution in the usual orthostatic reflex. In other words, chronic inactivity with frequent assumption of the supine position will lead to the hallmark signs of POTS. This raises the question as to whether, in some cases, POTS is actually an epiphenomenon, and has resulted from prolonged inactivity. Since many POTS sufferers feel compelled to remain supine, the potential for a vicious cycle is obvious.
Symptoms of POTS overlap with B12 deficiency in absence of anemia (folic acid fortification will correct the anemia once seen in B12 deficiency.) B12 deficiency cannot be ruled out with a complete blood count. Test B12 levels and the metabolites homocysteine and methylmalonic acid. http://www.aafp.org/afp/2003/0301/p979.html
The causes of POTS are not fully known. Most patients develop symptoms in their teenage years during a period of rapid growth and see gradual improvement into their mid-twenties. Others develop POTS after a viral or bacterial infection such as mononucleosis or pneumonia. Some patients develop symptoms after experiencing some sort of trauma such as a car accident or injury. Women can also develop POTS during or after pregnancy. These patients generally have a poorer prognosis.
In one large test, 12.5% of 152 patients with POTS reported a family history of orthostatic intolerance, suggesting that there is a genetic inheritance associated with POTS.[7]
So far no one has provided an explanation for POTS which is applicable to all sufferers, however there are many theories;
Alpha-receptor dysfunction may be occurring in some POTS patients.[8] Alpha-1 receptors cause peripheral vasoconstriction when stimulated. Alpha-1 receptor supersensitivity may be causing dysautonomia in some patients.[9]
Beta-receptor supersensitivity may occur with hyperadrenergic states in some people with POTS.[10]
Hyperdopaminergic states may be the underlying problem for some people with orthostatic intolerance. Some patients have been found to have a significant increase in upright dopamine levels.[11] Free plasma norepinephrine also tends to be higher in these patients.
Reduced venous return is one of the main mechanisms that causes POTS symptoms. Venous return can be reduced due to conditions such as hypovolemia (low plasma volume/low blood volume), venous pooling and denervation. A hyperadrenergic state may result as the body attempts to compensate for these abnormalities.
Anything that can damage the autonomic nervous system can potentially cause POTS. There are hundreds of things that can cause autonomic nerve damage, for example:
Additional causes of Autonomic Neuropathy are described on Medscape[18]
Sympathetic Overactivity is observed in many POTS patients. The sympathetic overactivity can be secondary to a number of factors, some of which may be peripheral denervation, venous pooling, or end-organ dysfunction. Sympathetic underactivity can also occur in some forms of orthostatic intolerance,[19] such as pure autonomic failure.
Recent studies have described a subset of POTS patients that appear to have elevated angiotensin II levels coupled with paradoxically reduced absolute blood volume, signs of increased sympathetic activity and reduced peripheral blood flow. This subset of POTS patients appear to have abnormal catabolism of Angiotensin II that may contribute to reduced blood volume and orthostatic intolerance.[20][21][22]
POTS can be difficult to diagnose. A routine physical examination and standard blood tests will not indicate POTS. A tilt table test is vital to diagnosing POTS, although all symptoms must be considered before a final diagnosis is made. Tests to rule out Addison's Disease, pheochromocytoma, electrolyte imbalance, Lyme Disease, Celiac Disease, and various food allergies are usually performed. A blood test may be performed to verify abnormally high levels of norepinephrine present in some POTS patients.
Between 75 and 80 percent of POTS patients are female and of the menstruating age. Most male patients develop POTS in their early to mid-teens during a growth spurt or following a viral or bacterial infection. Some women also develop POTS symptoms during or after pregnancy.
The timing of POTS becoming a named syndrome with no known cause coincides with the advent of folic acid fortification of foods and vitamins. Because the symptoms are the same symptoms as B12 deficiency in absence of anemia, and because the majority of the patients diagnosed with POTS have risk factors for new onset B12 deficiency (menstruating females, during a growth spurt, during or after pregancy) it is possible that POTS is a misdiagnosed B12 deficiency ("masked" by folic acid fortification, these patients no longer become anemic.) B12 deficiency must always be ruled out with any autonomous nervous system dysfunction. Failure to treat B12 deficiency with repletion of B12 may lead to irreversible damage. http://www.aafp.org/afp/2003/0301/p979.html
Most POTS patients will see symptom improvement over the course of several years. Those who develop POTS in their early to mid teens during a period of rapid growth will most likely see complete symptom resolution by their mid twenties. Patients with post-viral POTS will also usually improve greatly or see a full symptom resolution. Adults who develop POTS, especially women during or after pregnancy, usually see milder improvement and can be plagued with their condition for life. Rarely, a teenager who develops POTS will gradually worsen over time and have lifelong symptoms. Patients with secondary POTS as a consequence of Ehlers-Danlos Syndrome will also usually struggle with symptoms for life. In some patients the only cure for POTS is time.[23]
Recovered individuals do complain of occasional, non-debilitating recurrence of symptoms associated with autonomic dysfunction including dizzy spells, lightheadedness, flushing, transient syncope, and symptoms of irritable bowel syndrome. These symptoms are consistent with B12 deficiency in absence of anemia, which should always be ruled out directly by checking B12, homocysteine and methylmalonic acid. http://www.aafp.org/afp/2003/0301/p979.html
Most patients will respond to some form of treatment. Lifestyle changes, particularly drinking extra water and avoiding trigger situations such as standing still or getting hot, are necessary for all patients. Some patients also benefit from the addition of other treatments, such as certain medications.
Exercise is very important for maintaining muscle strength and avoiding deconditioning. Though many POTS patients report difficulty exercising, some form of exercise is essential to controlling symptoms and eventually, improving the condition. Exercises that improve leg and abdominal strength may aid in improving the muscle pump and therefore preventing pooling of blood in the abdomen and lower extremities.
Aerobic exercise performed for 20 minutes a day, three times a week, is sometimes recommended for patients who can tolerate it.[24] Certain modalities of exercise may be more tolerable initially, such as riding a recumbent bicycle or swimming. However, as tolerable, upright exercise may benefit the participant through orthostatic training. All exercise programs for POTS patients should begin with low intensity exercises for a short duration and progress slowly.
Patients whose POTS symptoms are due to B12 deficiency need pharmacological doses of B12 for repletion of tissues. http://www.aafp.org/afp/2003/0301/p979.html
Several classes of drugs often provide symptom control and relief for POTS patients. Treatments must be carefully tested due to medication sensitivity often associated with POTS patients, and each patient will respond to different therapies in different ways.
The first drug of choice for symptomatic relief of POTS is usually fludrocortisone, or Florinef, a mineralcorticoid used to increase sodium retention and thus increase blood volume and blood pressure. An increase in sodium and water intake must coincide with fludrocortisone therapy for effective treatment.
Dietary increases in sodium and sodium supplements are often used.
Beta blockers such as atenolol, metoprolol and propanolol are often prescribed to treat POTS. These medications slow down the excessive heart rate response (tachycardia) that POTS patients experience. They also work by blocking the effects of epinephrine and norepinephrine released by the Autonomic Nervous System. In addition, beta blockers reduce Sympathetic Nervous System activity by blocking Sympathetic impulses. For some patients, Beta blockers increase POTS symptoms (e.g. lowering blood pressure, increasing fatigue, which is why they are often prescribed in conjunction with Midodrine). Beta blockers may be dangerous to individuals with asthma or allergies.
Midodrine (Proamatine), is approved by the U.S. Food and Drug Administration (FDA) to treat orthostatic hypotension, a condition related to POTS. It is a stimulant that causes vasoconstriction and thereby increases blood pressure and allows more blood to return to the upper parts of the body. Use of midodrine is often discontinued due to intolerable side-effects, and it is known to cause supine hypertension (high blood pressure when lying down). Some doctors prefer to start patients on Midodrine without the concomitant use of Beta blockers and then add Beta blockers once the dose of Midodrine has been properly adjusted. This gives the Midodrine time to start raising the patient's blood pressure which often helps avoid the hypotension that is a common side effect of Beta blockers. Obviously lowering the blood pressure of a POTS patient would exacerbate any existing orthostatic hypotension.
Antidepressants, especially selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac), sertraline (Zoloft), citalopram (Celexa), escitalopram (Lexapro), and paroxetine (Paxil), can be extremely effective in re-regulating the autonomic nervous system and raising blood pressure. Some studies indicate that serotonin-norepinephrine reuptake inhibitors (SNRIs) such as venlafaxine (Effexor) and duloxetine (Cymbalta) are even more effective. Tricyclic antidepressants, tetracyclic antidepressants, and monoamine oxidase inhibitors are also occasionally, but rarely, prescribed. A combination of two antidepressants, usually an SSRI or SNRI with bupropion (Wellbutrin) or mirtazapine (Remeron), is also shown to be very effective.
Medications used to treat attention deficit disorder and attention deficit hyperactivity disorder such as methylphenidate (Ritalin) and Adderall effectively increase norepinehprine and dopamine levels, thereby increasing vasoconstriction and blood pressure.
In some cases, when increasing oral fluids and salt intake is not enough, intravenous saline is used to help increase blood volume, as many POTS patients suffer from hypovolemia.[25][26] Increasing blood volume can decrease POTS symptoms caused or worsened by low blood volume such as tachycardia, low blood pressure, fatigue and syncope. Infusions can be taken on an as needed basis in an Emergency Room, or on a regularly scheduled manner at an infusion center or at home with the assistance of a home care nurse.
In the UK Ivabradine has been used to treat patients with POTS symptoms with good effect. Ivabradine acts by reducing the heart rate in a mechanism different from beta blockers and calcium channel blockers, two commonly prescribed antianginal drugs. It is classified as a cardiotonic agent.
Pressure garments can reduce symptoms associated with orthostatic intolerance by constricting blood pressures with external body pressure.
Compression devices, such as abdominal binders and compression stockings, help to reduce the amount of pooling blood. Compression stockings should be at least 30–40 mm Hg and will work best if they are waist high.[28] Compression stockings should be fitted to achieve the greatest benefit. If the patient find 30-40mmHg compression stockings to be too unfomfortable, consider a lesser compression, such as 20-30mmHg. Many patients see improvement with that level of compression, preferrably full length/waist high stockings.
Compressions suits (G-Suits) have also been used with some good results.[29][30]
Some patients report that symptoms worsen with changes in barometric pressure (for instance, before a thunderstorm) and changes from outdoors to indoors (presumably barometric pressure is higher inside) and depending on weight of clothes and coverage. These patients may find relief by moving to a new location where barometric pressure is relatively stable, e.g. San Diego.[31][32][33]
POTS was first named and identified by Schondorf and Low in 1993;[34] however, the syndrome has been described in medical studies dating back to at least 1940. Hypertension associated with POTS has been previously described as the "hyperadrenergic syndrome" by Streeten and as "idiopathic hypovolemia" by Fouad.[35] Hypotension associated with POTS has been previously described as the "neurally mediated hypotension" form of POTS.
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