Postural Tachycardia Syndrome

INTRODUCTION

Most people take the act of standing for granted. They do not think about the gravitational stress that standing places on the body. In most cases, the normal mechanisms we have to keep a normal blood pressure and heart rate despite standing operate well without our realizing this is going on. Sometimes, however, the process can be disrupted by a problem with the part of our body that controls the automatic functions of the body (the autonomic nervous system or ANS). One type of ANS disturbance is referred to as the Postural Tachycardia Syndrome (or POTS).

NORMAL RESPONSES TO STANDING

When a normal individual stands, the effect of gravity will cause 25% or more of the body’s blood volume to be displaced downward into the lower half of the body. This can be anywhere from 500 to 1000 cc of blood. (Figure I) This displacement of blood into the lower part of the body is perceived by the brain via special fibers (called c-fibers or mechanoreceptors) that are located in the walls of blood vessels. The greater the degree or stretch on these vessels, the greater the degree of electrical activity these cells send to the brain. Once the brain has determined that a large displacement of blood has occurred, it gives instructions to the body to correct for it. This response has 3 major components: an increase in the rate at which the heart beats, an increase in the force with which each beat of the heart contracts, and, most importantly, an increase in the constriction (tightness) of the blood vessels in the lower half of the body (especially the veins). These three actions, working together, force blood into the upper part of the body almost immediately after standing, thereby ensuring a constant supply of blood to the brain regardless of position. While hormonal factors also play a role in this process, they do so over much longer time periods.The aspect of the human nervous system that governs the immediate response changes in position is referred to as the autonomic nervous system. (The word “autonomic” is derived from the same Greek root as the word “automatic” or self governing). The autonomic centers of the brain (located in the posterior aspect or “brain stem”) control not only heart rate and blood pressure, but also body temperature, sweating, urinary, digestive, and sexual function. A failure of the autonomic system to function appropriately, or in a coordinated fashion, may result in a failure of any of the aforementioned functions to work normally. This state of “autonomic failure” is referred to by some as “dysautonomia.” POTS is one type of dysautonomia. Frequently, if one of the three responses to upright posture fails to operate appropriately, the brain will increase the activity of the remaining two as compensation. In POTS, there is usually a failure of the blood vessels in the lower body to achieve or maintain normal tightness when standing (and on occasion sitting) thereby allowing excessive blood to accumulate in the lower body. The brain then causes the heart to beat faster and harder while upright in an attempt to compensate. Thus, when standing, the POTS patient would feel his heart pounding in his chest (palpitations) and at an abnormally fast rate (tachycardia). While initially compensatory, if the failure to maintain vascular constriction worsens, it will eventually reach a point where these compensations will no longer be adequate to maintain blood pressure at a constant level and the amount of blood the brain receives while standing will decline.

HISTORICAL ASPECTS

In 1871 the American physician, DeCosta, described a condition he called “Irritable Heart Syndrome” in a group of patients who complained of palpations, extreme fatigue, inability to exercise, dizziness, and fainting. Each patient displayed a striking increase in heart rate upon standing. In 1919, the English physician, Sir Thomas Lewis, described a condition he called “The Effort Syndrome,” characterized by a fall in blood pressure on standing associated with an excessive increase in heart rate when the affected patient stood. The patients he described complained of excessive fatigue, dizziness, lightheadedness, fainting, and inability to exercise. He postulated that there was an excessive amount of blood accumulation in the veins of the lower extremities that caused the condition. The term Postural Tachycardia Syndrome was first used by the American physician, McClean, in 1944 who described an identical group whose symptoms appeared to be caused by venous pooling of blood in the lower extremities.

The term Postural Orthostatic Tachycardia Syndrome (POTS) was first used in the early 1990’s to describe a group of patients who displayed dramatic increases in heart rate upon standing (usually greater than 30 beats per minute or rates that exceeded 120 beats per minute) that occurred in the absence of any other identifiable cause (such as dehydration or the affect of a drug the patient was taking). The patients complained of palpitations, heart racing, and fatigue, inability to exercise, shortness of breath, lightheadedness, and fainting. The majority of patients reported have been women (with a close to 5:1 ratio), but it can also affect children, adolescents, and adults of either gender.

CLINICAL CHARACTERISTICS

POTS does not appear to be a single disorder, but rather a collection of different disorders with similar clinical manifestations. There are different ways that the subtypes of POTS can be organized. The classification presented here is the one used at the Autonomic Disorders Clinic at the University of Toledo Medical Center. POTS can be subclassified into primary and secondary forms. The primary forms occur in the absence of other diseases and the secondary forms occur as a consequence of another disease (for example, diabetes). The primary forms of POTS can be divided into 2 major subgroups: peripheral dysautonomic and hyperadrenergic.

The peripheral dysautonomic (PD) form is the most common. As was mentioned earlier, these individuals seem to have a failure of the lower body vasculature (especially the veins) to maintain adequate tightness while upright. To compensate for this, the heart rate and the force with which the heart contracts will increase. Many patients will report an exact triggering event that coincided with the development of symptoms. The most common of these are viral infections, as well as pregnancy and trauma (motor vehicle accidents, lightning injury, and electrocution). Some patients will not recall any triggering event. In addition to severe fatigue, exercise intolerance, palpitations, tachycardia, syncope (fainting), and near-syncope, many patients complain of severe memory problems and difficulty concentrating. Symptoms are often worse in the morning and are exacerbated by extreme heat.

While the cause of the PD form of POTS is unknown, there is increasing evidence that in some patients it is an autoimmune disorder (the body’s own immune system making antibodies against the autonomic nerves). Further studies looking at this are underway.

A distinct form of PD POTS appears to occur in young people, which we refer to as the “developmental” form. Onset of symptoms is usually around age 14 years, and often follows a period of rapid growth. The majority of these patients are young women. Some patients are severely affected to the point of being disabled. Many will have urinary and gastrointestinal problems as well. However, the majority of the patients with the developmental form of POTS will eventually improve over time. Around 80% recover by the time they are in their mid 20’s.

The hyperadrenergic form of POTS is far less common and accounts for around 10% of POTS patients. As opposed to patients with the PD form of POTS, patients with the hyperadrenergic form tend to report a slower, more gradual onset of symptoms. Many of these patients tend to complain of anxiety, shakiness, and cold sweaty arms and legs while standing. About one half of hyperadrenergic POTS patients complain of migraine headaches. Some of these patients will display high blood pressure while standing and most will have blood serum levels of norepinephrine while standing. Hyperadrenergic POTS tends to run in families. There is evidence to suggest that hyperadrenergic POTS is a genetic disorder involving a mutation in a protein that recycles norepinephrine in the spaces between nerves (the intersynaptic cleft).

The term “secondary POTS” is employed to describe POTS-like symptoms that occur due to another illness. The most common cause of secondary POTS is diabetes mellitus. (Other causes include diseases such as amyloidosis, sarcoidosis, and alcoholism.) Another important cause of secondary POTS is the condition called Joint Hypermobility Syndrome (JHS). This is a genetic condition which results in replacement of certain types of collagen (a basic building block of the body) which then causes hypermobility of the joints, and skin that is soft (almost velvet like) which can bruise easily. Some patients may also complain of varicose veins as well as muscle and joint pain. It can also produce a POTS-like state because blood vessels (especially veins) are overly elastic and cannot maintain adequate tightness while a person stands, allowing a greater than normal degree of blood pooling in the lower extremities with a resultant compensatory tachycardia.

On rare occasions, POTS may be the presenting sign of more serious disorders such as Pure Autonomic Failure and Multiple Systems Atrophy. POTS may also be the presenting symptom of some forms of cancer.

 

EVALUATION AND MANAGEMENT

The first step is for the physician to do a careful history and physical examination. It is important to check the blood pressure and pulse while lying, sitting, and standing. In many patients, additional testing may be necessary to better define the diagnosis. One such test is referred to as Tilt Table Testing (the details of which are discussed elsewhere). Sometimes blood tests for the levels of catecholamine (epinephrine and norepinephrine) are performed.

Patients are also encouraged to avoid conditions that make them worse, such as excessive heat, alcohol, or dehydration. They are also advised to discontinue medications which may be worsening the condition. In addition, adequate fluid intake is also encouraged. In the PD form, increased salt intake is also advised.

Reconditioning of the patient with POTS is of paramount importance. The aim of reconditioning is to improve the strength of the legs and thereby increase the effectiveness of the skeletal muscles to pump and return blood to the heart. This is best accomplished by a combination of aerobic exercise and resistance (weight) training. Often, water exercises (such as swimming) are the most comfortable for the patient.

A number of medications have been found to be helpful in relieving symptoms in patients with POTS (although no drug has been approved by the United States Food and Drug Administration for the treatment of POTS). The drugs used have been approved for other indications, but also have been shown to be useful in treating POTS.

These include:

1. Fludrocortisone
2. Midodrine
3. Methylphenidate
4. Pyridostigmine
5. Serotonin Re-uptake inhibitors
6. Norepinephrine Reuptake inhibitors
7. Clonidine
8. Labetalol

More in depth discussions of these and other medications can be found elsewhere.

There is only limited information available on the prognosis of patients with POTS. Some studies have reported that around half of patients with the post viral forms improve over a 2 to 5 year period. It appears that the younger the patient the better the prognosis. About 70% of adolescents with the development form of POTS will have significant recovery by the time they reach their mid 20’s. Almost 90% of patients will respond to a combination of physical therapy and pharmacotherapy.

Figure 1: Normal Responses to Standing

(Drawing by Helen Grubb) 

 

Dedication

 To Barbara Straus, M.D. wife, mother, physician, dancer and soul mate; source of all inspiration.

Web Resources

www.utoledo.edu  The University of Toledo, Medical College

www.DINET.ORG Dysautonomia Information Network

www.dynakids.org Dysautonomia Youth Network of America

www.NDRF.org     National Dysautonomia Research Foundation

www.STARS.org.uk Syncope Trust UK

Book about POTS

1. Grubb BP. The fainting Phenomena (second edition) Blakwell/Futura Press, Malden MA 2007
2. Grubb BP, Olshansky B. Syncope: Mechanisms and Management. (second edition) Blackwell/Futura Press, Malden MA 2005.

 

References

1. Grubb BP, Kanjwal Y, Kosinski D. The Postural Tachycardia Syndrome: A concise guide to diagnosis and management. Journal of cardiovascular Electrophysiology 2006;14:108-112
2. Grubb BP. Postural Tachycardia Syndrome. Circulation 2008:117
3. Medow MS, Stewart JM. The Postural Tachycardia Syndrome. Cardiology Review. 2007; 15:67-75
4. Thieben M, Sandroni P, Sletten D, et al. Postural Tachycardia Syndrome: The Mayo Clinic Experience. Mayo Clinic Proceedings. 2007;82:308-313