POTS Syndrome

What is POTS Syndrome?

The autonomic nervous system disorder when interferes the heart rate increment due postural changes is termed as POTS Syndrome (postural orthostatic tachycardia syndrome). Clinical presentation illustrates that tachycardia (almost more than 120 beats / min) in standing posture, followed almost 30 beats/min or more increased heart rate than the normal heart rate after maintaining the posture for 10 min along with different clinical symptoms.

Signs & Symptoms

The increased heart rate is the prime sign of the POTS syndrome. But other than this, the involvement of complex sign can be demonstrated as blood pressure fluctuation.

In most of the patients, blood pressure is dropping down, but in some cases increase blood pressure is also noticed, even no blood pressure alteration may also be associated with POTS. The included symptoms are:

• Fatigue
• Lightheadedness
• Headaches
• Nausea
• Lack of concentration
• Tremor
• Dizziness
• Sweating
• Fainting (syncope)
• Pain in upper and lower limb
• Palm and feet become cold
• Exhaustion intolerance
• Palpitations
• Chest pain
• Shortness of breathing

Reddish purple color in the lower extremities while standing and disappear the color change with resting position. The reddish purple color is developed due to poor circulation. Blood is pooled from the lower extremities for maintaining  the circulation.

Etiology

The hypovolemia or low blood volume and increase level of norepinephrine (autonomic neurotransmitter) in blood plasma are responsible factor to enhance the sympathomimetic stimulation. Activation of sympathetic nervous system is the causative factor to initiate the increased heart rate. The observed report findings revealed that half of the patients having POTS have a mild fiber neuropathy, which stimulates the sweat glands by activating the sudomotor nerve.

Some mutagenic changes responsible for the gene encoding for increased transportation for norepinephrine. Ala 457pro mutation transports norepinephrine. Norepinephrine has an agonist effect on autonomic nervous system ( sympathetic action), which leads to increase heart rate.

Incidence rate

Low et al from the Mayo clinic first described the POTS in the year 1940. Frolich et al described that without changes of blood pressure can also develop  symptomatic postural tachycardia.

The incidence rate is high in young aged females, and survey reveals that the relationship of incidence rate in the age between 12 to 50 years of females and that is expressed in  a ratio of 5:1. This incidence rate is higher or more common after infection, physical or mental stress, high fever, pregnancy, surgery or trauma.

Pathogenesis

The factors influence the POTS are included abnormality which affects the nervous system surrounded the vascular beds, higher concentration of norepinephrine in blood  plasma, stimulation of the α‐receptor, excessive stimulation of the β‐receptor, defective baroreflex mechanism.

Impaired vascular innervation stimulates the sympathetic nervous system and leads pathogenic  changes requires for the POTS. Often dysfunctional vascular bed cause reduced cardiac output and leads more pooling of blood from the lower extremities and venous return become lower down. Consequently redistributed peripheral circulation takes place, which leads to hypovolaemia  and condition becomes worsen with capillary leakage. Reflex tachycardia is generated to establish the homeostasis, but associated vasoconstriction has not taken place and central venous pressure becomes lower down and patient may faint.

Types of POTS

POTS  is two types – primary and secondary. This classification is based on the underlying reason of POTS onset.

Primary POTS

The reason behind the onset of primary POTS are partial dysfunction in autonomic nervous system, immune system pathogenic interference in the immune system, adolescence and blood pressure changes.

Secondary POTS

The reasons behind the onset of secondary POTS Syndrome are high blood sugar, downfall of  amyloid in the physiological system, heavy metal poisoning, drying of saliva and/ or tears (Sjogren syndrome) due to immune system disorder, excessive movements of the joints beyond the range (hypermobility syndrome) and distorted immune system reaction against neoplasm  (paraneoplastic syndrome).

Diagnosis

The following test is conducted for confirming the presence of POTS in case of suspected cases.

Hematological test

The included tests under the blood tests are Full blood count, blood glucose level, thyroid function tests, electrolytes, serum cortisol and bone profile.

ECG

The ECG (electrocardiogram) is used to evaluate the muscular  and electrical functionality of the heart.

X ray

X ray image is taken to check the cervical vertebrae, because any abnormality can affect the  overall circulation.

Catecholamine levels

The blood test and urine analysis are conducted for checking the catecholamine level, as increased catecholamine level provoke autonomic nervous system stimulation.

70° head tilt table test

This is the gold standard test to identify the orthostatic balance and also followed the neurovascular competency test. Alteration of heart rate and involvement of the blood pressure response help to identifying the type of orthostatic intolerance is persistent, which help to make the most effective treatment plan for treatment of the POTS.

Other than the above mentioned tests, additional tests like EEG, CT scan of the brain, fibrosis or thermoregulatory sweat testing and sudomotor function test is conducted depending upon the above mentioned test result and for identification of the underlying cause.

Treatment

Pharmacological and non- pharmacological treatment measure can prevent and improve the POTS Syndrome.

Pharmacological Measures

There is no specific treatment for POTS, but medicine prescribed for treating the POTS Syndrome is depends upon the underlying cause and symptomatic relief. The prescribed medicines are:

Fludrocortisone

It helps to rise sodium and fluid retention  and also provide agonistic effect on α‐adrenergic receptors, so blood pressure  is not going down.

Midodrine

This is an analogue of Antidiurectic hormone and acts as vasoconstriction by stimulating  α‐1 receptor and improve orthostatic tolerance.

Methylphenidate

This is providing effective treatment for POTS Syndrome as it provides sustained action by acting as α‐agonist.

Erythropoietin

It has a direct vasoconstrictive effect with increase volume expansion. But this drug is not frequently prescribed, as it is expensive and available dose is given via subcutaneous route.

Labetalol

For some patient,  labetalol is prescribed. It acts as α‐ and β‐receptor blocking effects.

Clonidine

This drug blocks the sympathetic nerve action.

SSRIs

Selective serotonin reuptake inhibitors helps to maintain the baro-reflex which stimulate the standing vasoconstriction reflex and also maintain the better nerve communication. It helps to reduce the symptomatic relief of the POTS.

NRI

Norepinephrine reuptake inhibitor also helps to reduce the symptomatic relief of the POTS.

Pyridostigmine

This medicine is specifically prescribed for the patient, who suffers from autoimmune disorders or post‐viral infection and shows potential results.

Non-pharmacological therapy

• Regular aerobic exercise helps to maintain the improved venous return to the heart from the lower limbs.
• Keep hydrated by drinking adequate water, which contain the proper balance of minerals.
• It is suggested that wearing of compression stocking helps to control the symptoms associated with POTS syndrome, as it helps to raise the standing pressure at the calf muscle and reduce venous pooling from the lower extremities.

Prognosis

The prognosis depends upon the underlying cause. In case of post viral syndrome, often patients recover within two to five years. Younger aged person recover fast rather than older aged individual. The combination of pharmacological therapy with regular physical activity provides better prognosis. Hyperadrenergic etiology needs lifelong treatment, whereas secondary POTS often recover after the  underlying cause is controlled.

References

1. Postural Orthostatic Tachycardia Syndrome; Retrieve from: http://www.dysautonomiainternational.org/page.php?ID=30
2. A K Agarwal, R Garg, A Ritch, and P Sarkar (2007); Postural orthostatic tachycardia syndrome; Postgrad Med J. 2007 Jul; 83(981): 478–480; Retrieve from:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600095/
3. Postural Tachycardia Syndrome (POTS); Rare Disease Clinical Research Network; Retrieve from: https://www.rarediseasesnetwork.org/ARDCRC/patients/learnmore/POTS/