The postural tachycardia syndrome (POTS) is a disorder of young people and usually becomes manifests between ages 14-45. It is characterized by an abnormal increase in heart rate without a significant change in blood pressure upon standing.
POTS is 4-5 times more common in women than men.
It is important not to confuse POTS with orthostatic hypotension, a common problem, particularly among elderly people
POTS is a heterogeneous group of disorders with similar clinical manifestations. This means that the underlying cause varies between individuals, and so does the general clinical picture.
POTS itself is not a disease but rather a cluster of symptoms that frequently occur together. Hence, the term ‘syndrome’.
POTS is regarded as being either primary or secondary. The primary forms are not associated with any known disease, whereas the secondary types occur together with a known disease or disorder (3).
Before we go further, we must understand two terms;
- orthostatic intolerance
- autonomic dysfunction (dysautonomia)
The term orthostatic intolerance is used to describe different types of discomfort upon assuming the standing position.
In clinical medicine, the term orthostasis refers to the normal response of the sympathetic nervous system to counteract a fall in blood pressure when a person assumes the upright position after lying down.
What happens when we stand up from a supine position is that 500 to 800 mL of blood volume is shifted from the upper body to the lower body and abdominal organs. Consequently, the venous return of blood to the right side of the heart diminishes. Lower blood volume within the heart chambers then leads to a reduction in the stroke volume from the heart which eventually can lead to a fall in blood pressure (4).
Usually, due to several compensatory mechanisms controlled by the autonomic nervous system, the body quickly counteracts this response and maintains stable blood pressure and blood flow. Hence, in most people, the drop in blood pressure is only transient and goes unnoticed (5).
However, if the body’s regulatory responses are disturbed or delayed, orthostatic intolerance may occur.
POTS is a relatively common cause of orthostatic intolerance in younger individuals.
Orthostatic Hypotension Should Not Be Confused with POTS
Orthostatic hypotension is one form of orthostatic intolerance.
The classical definition of orthostatic hypotension is a reduction of at least 20 mm Hg in systolic or of at least 10 mm Hg in diastolic blood pressure, measured 3 minutes after changing from a lying to a standing position.
Several factors may contribute to orthostatic hypotension.
Drug-induced autonomic failure is probably the most frequent cause of orthostatic hypotension.
Medications that are used to treat elevated blood pressure, such as beta-blockers, calcium channel blockers, ACE inhibitors, nitrates, and angiotensin II blockers, can induce orthostatic hypotension. Some medications for anxiety, depression, erectile dysfunction, and Parkinson’s disease may also have similar effects.
Hypovolemia (a drop in the volume of blood) and dehydration both promote orthostatic hypotension.
The risk of orthostatic hypotension increases with age. This may be due to impaired autonomic reflex response and the use of medications that promote low blood pressure.
Patients with diabetes and certain nervous system diseases are at increased risk of orthostatic hypotension due to autonomic dysfunction.
Orthostatic hypotension should not be confused with POTS, which is another cause of orthostatic intolerance.
Autonomic Dysfunction (Dysautonomia)
In autonomic dysfunction, altered function of the autonomic nervous system adversely affects health (6).
The primary role of the autonomic nervous system is to maintain homeostasis by using complex neural and chemical signals to control the interaction between various organ systems in the body.
Homeostasis, from the Greek words for “same” and “steady,” refers to any process that living organisms use to actively maintain fairly stable conditions necessary for survival (7).
The autonomic nervous system is made up of pathways of neuronal cells (neurons). It is divided into the sympathetic and parasympathetic systems. The sympathetic component is better known as “fight or flight” and the parasympathetic part as “rest and digest.”
Stimulation of the sympathetic nervous system leads to a fast heartbeat (tachycardia), whereas stimulation of the parasympathetic nervous system leads to a slow heartbeat (bradycardia).
Norepinephrine (noradrenaline) is the primary chemical messenger of the sympathetic nervous system, whereas acetylcholine is the main chemical messenger of the parasympathetic nervous system.
The autonomic nervous system functions without conscious control throughout our lifespan. It controls heart rate, the force of contraction of the heart muscle, smooth muscle, and exocrine and endocrine glands, which in turn regulate blood pressure, urination, bowel movements, and thermoregulation (8).
The term autonomic dysfunction or dysautonomia refers to altered function of the autonomic nervous system that may lead to a diversity of symptoms depending on the nature of the autonomic failure.
POTS is a relatively common cause of dysautonomia in younger individuals.
Definition and Clinical Features of POTS
POTS has been known by many other names throughout history, such as DaCosta’s syndrome, Soldier’s heart, mitral valve prolapse syndrome, neurocirculatory asthenia, and effort syndrome.
In 1982, Rosen and Cryer were the first to use the term postural tachycardia syndrome (9).
POTS can strike at any age but is most common among women between ages 15 to 50.
POTS is characterized by orthostatic intolerance caused by dysautonomia. Fast heartbeat (tachycardia) upon resuming the standing position is a must-have. Hence, POTS is a subset of orthostatic intolerance that is associated with the presence of excessive tachycardia on standing.
POTS is currently defined as the presence of symptoms of orthostatic intolerance associated with a heart rate increase of 30 bpm (or rate that exceeds 120 bpm) that occurs within the first 10 minutes of standing, not associated with orthostatic hypotension or other chronic debilitating conditions such as prolonged bed rest or the use of medications known to diminish vascular or autonomic tone (3).
Patients with POTS usually report dizziness, lightheadedness, weakness, and blurred vision, and fatigue upon standing (1). Other common complaints include palpitations, exercise intolerance, nausea, diminished concentration, tremulousness, and fainting.
More than 75% of patients with POTS experience general fatigue as a major complaint.
The severity of symptoms is quite variable. Some patients experience only mild symptoms, whereas others have symptoms of such severity that normal activities of life, such as bathing, housework, and even eating, can be significantly limited.
In some cases, the disorder may be self-limited. In other cases, it may follow a relapsing-remitting course over several years.
A significant minority of patients report a viral-like illness before the onset of POTS.
Diagnosis of POTS
The principal feature of POTS is orthostatic intolerance associated with rapid heart rate (tachycardia), defined as the provocation of symptoms on standing that are relieved by recumbence (4).
POTS is characterized by the following:
- A specific group of symptoms that frequently occur when standing upright
- A heart rate increase from horizontal to standing of at least 30 beats per minute in adults, or at least 40 beats per minute in adolescents, measured during the first 10 minutes of standing
- Sustained tachycardia for more than 30 seconds
- Absence of orthostatic hypotension
POTS can be diagnosed by measuring heart rate and blood pressure in the supine (lying down) position and standing up position at 2,5 and 10-minute intervals (11).
It is relatively common for patients with POTS to have a drop in blood pressure upon standing. However, many patients have no change or even an increase in blood pressure upon standing (3).
Different Forms of POTS
Although dysautonomia is an underlying problem in patients with POTS, the exact cause may be difficult to determine.
When an underlying cause cannot be found, POTS is defined as primary or idiopathic.
POTS is considered secondary if it is associated with a known underlying disease or disorder.
The most common form of primary POTS is the “partial dysautonomic” form. These patients have a much greater than normal degree of blood pooling in the dependent areas of the body (legs, lower arms, and abdominal organs) while upright. This initially leads to a compensatory increase in heart rate in an attempt to maintain blood flow to the brain.
Although the increase in heart rate may initially be compensatory, the extent of peripheral venous pooling of blood can continue to increase over time and exceed this compensatory effect. The patient then becomes increasingly dependent on the skeletal muscle pump to augment venous return and maintain adequate blood pressure. However, the degree of venous pooling may continue to increase and overcome this compensatory effect, leading to POTS (12).
The majority of patients with the partial dysautonomic form of POTS are women (13).
A second (and less frequent) form of POTS is termed the “hyperadrenergic” form (14). These patients often complain of significant tremor, anxiety, and cold sweaty extremities while upright. Over half of these patients experience migraine headaches as well as a substantial increase in urinary output after being upright for only a short period of time.
A characteristic of this form of POTS is that patients have an increase in systolic blood pressure of at least 10 mmHg within 10 minutes of standing in addition to tachycardia. The disorder often has a strong family history.
The term secondary POTS is used to describe a variety of conditions that are associated with dysautonomia. Diabetes mellitus is a frequent cause of secondary POTS. Examples of other conditions related to POTS are amyloidosis, sarcoidosis, alcoholism, lupus, Sjögren syndrome, and chemotherapy.
Patients with Ehlers-Danlos syndrome, a group of inherited disorders involving joint mobility, often have POTS.
POTS also occurs quite commonly alongside chronic fatigue syndrome (15).
The Management of POTS
Because of the heterogeneity of POTS, treatment has to be tailored to the patient’s clinical picture.
Firstly, in all patients, dehydration and inactivity should be avoided.
Any drug that could be contributing to the symptoms should be discontinued if possible. Examples of such medications are diuretics, some antidepressants, and attention deficit medications. Stimulants, including caffeine and nicotine, may also exacerbate symptoms.
Increased fluid and salt intake are advisable for most patients. At least 2-3 L of water accompanied by 10-12 g of daily sodium is often recommended (16).
Exercise programs are encouraged but should be introduced gradually, working toward a goal of performing 20 to 30 minutes of aerobic activity 3 times a week.
Elastic compression stockings are sometimes helpful; the most effective ones are waist high and provide at least 30 to 40 mm Hg of ankle counter pressure.
In patients suffering from the partial dysautonomic form of POTS, initial therapy is directed at augmenting fluid volume and increasing peripheral vascular resistance.
Up to 70 percent of patients with POTS have hypovolemia (low blood volume)(16). Intermittent infusion of 1 L of normal saline has been found to significantly reduce symptoms and improve the quality of life in these patients (17). However, long-term use of saline infusion should be used with caution because of the risk of infection.
Drug Treatment for POTS
Drug therapy is reserved for patients who do not improve by general and lifestyle measures.
Fludrocortisone, a synthetic aldosterone analog, is usually well tolerated. It is used to augment blood volume, starting at 0.1 to 0.2 mg per day.
An alternative agent is desmopressin acetate (DDAVP) 0.1 mg to 0.2 mg orally at bedtime.
If needed, a vasoconstrictor such as midodrine may be added, 5 mg orally 3 to 4 times daily.
In patients who are not responsive to or intolerant to these therapies, either a serotonin reuptake inhibitor (SSRI) or norepinephrine (noradrenaline) reuptake inhibitors can be added. If an SSRI is used, those with a combined serotonin-norepinephrine effect (duloxetine and venlafaxine) appear to work best.
A promising new therapy is pyridostigmine (Mestinon), an acetylcholinesterase inhibitor that is thought to facilitate ganglionic neural transmission in both the sympathetic and parasympathetic nerves (18).
Erythropoietin (EPO) has been used in patients who are severely affected by POTS and in whom no other therapy is effective or tolerated. Although initially introduced to treat anemia, EPO has been found to process potent vasoconstrictive effects with demonstrated utility in treating orthostatic disorders (19).
Beta adrenergic blockers, such as propranolol, can reduce standing heart rate and improve symptoms in some patients. These should be started in low doses and increased gradually up to 20-30 mg three times daily.
The combined alfa and beta blocking drugs labetalol and carvedilol are quite useful in some patients, as pure β-blockers may exacerbate symptoms.
Clonidine and methyldopa have been reported to be useful in some patients, as has phenobarbital.
The Prognosis of POTS
Limited data are available on the long-term prognosis of POTS. However, although not shown to shorten life, POTS can be physically and mentally debilitating (20).
Currently, there is no cure for POTS. However, it is believed that most patients will see an improvement in symptoms over time.
For the most part, the younger the patient, the better the prognosis. In general, close to 90% of patients will respond to a combination of physical therapy and pharmacotherapy (3).
Patients with the hyperadrenergic form of POTS usually require therapy indefinitely.
The prognosis of patients with secondary POTS is usually determined by the prognosis of the underlying disorder.