Postural tachycardia syndrome

Refers to the combination of an exaggerated heart rate response to standing, in association with symptoms of lightheadedness or pre-syncope that improve when recumbent.

An autonomic disorder commonly occurs after a viral or bacterial infection, and is characterized by brain fog, fatigue, lightheadedness, and increased heart rate upon standing.

Symptoms are also seen in  people with post acute sequel of COVID-19.

The condition is often associated with fatigue and brain fog.

Can result in disruptions in adolescence and young adulthood.

Prevalence estimated to be 170 cases per 100,000 individuals.

It is a chronic debilitating condition characterized by symptoms of lightheadedness, fatigue, palpitations, pre-syncope.

Also associated with sleep disturbances, cognitive impairment, increase in heart rate when upright, despite maintenance of a normal blood pressure.

Patients commonly report palpitations, dizziness, and visual disturbances that often improve when recumbent.

Symptoms of fatigue and difficulties with cognition are less responsive to postural movements.

Increased heart rate, or exaggerated heart rate defined as a sustained increment >30 beats per minute (bpm) in adults, or >40 bpm in children, that occurs within 10 minutes of standing.

Two main subtypes are neuropathic POTS involving reduced noradrenergic vasoconstriction in the extremities or the splanchnic vasculature and hyperadrenergic POTS involving excessive noradrenergic vasoconstrictor, reduced calf blood flow, and prominent symptoms of sympathetic activation.

Onset of symptoms may be gradual and can be triggered by an infective illness.

Associated with a higher prevalence of joint hypermobility and chronic fatigue syndrome.

Occurs more commonly in adolescent females.

Rare over the age of 40 years.

The pathophysiology likely to be multifactorial and includes: such as moderate autonomic dysfunction, increased sympathetic tone, deconditioning, inadequate venous return or excessive blood venous pooling

Symptoms occur when upright, despite maintenance of a normal blood pressure.

The nonspecifc nature of symptoms, makes it difficult to establish the true prevalence.

Autoimmunity and mast cell activation syndromes have been postulated as contributing to the etiology in some patients, but remain controversial.

Therapies are few and directed toward symptom control by either increasing intravascular volume, increasing peripheral vascular tone or controlling heart rate.

Response to therapeutic interventions is highly variable.

Concurrent irritable bowel syndrome, food intolerance and allergic sinus- itis, are commonly reported.

Plethysmography may demonstrate splanchnic venous pooling in patients with IBS.

Some concurrence of IBS and POTS.

The treatment of POTS may improve IBS symptoms.

Concurrent hypermobility is ov2242epresented

Anxiety, chronic fatigue syndrome and either hypermobility or POTS has been reported by several groups.

Vascular compression syndromes are associated with POTS include median arcuate ligament syndrome, thoracic outlet syndrome and pelvic compression syndrome with POTS, presumably due to the reduction in venous return that may occur with these conditions.

Median arcuate ligament syndrome is an uncommon condition in which patients develop postprandial or postexertional abdominal pain secondary to intermittent obstruction of celiac or superior mesenteric arteries by the median arcuate ligament, sometimes in association with celiac plexus compression.

Thoracic outlet syndrome describes the association of symptoms provoked by muscle, fascial or bony compression of vascular structures or nerves at the thoracic outlet.

The peripheral and splanchnic vessels are most commonly implicated as the sites of venous pooling in POTS.

Pelvic vein varicosities may also result in signicant venous pooling.

Patients frequently present after a prolonged period of illness, and orthostatic intolerance has developed as a result of deconditioning, disrupted circadian rhythm or dietary deficiencies.

The distinction between chronic fatigue syndrome, fibromyalgia and POTS is often blurred, with a signicant overlap in symptoms.

Some patients develop symptoms following a period of rapid growth while others recall a traumatic or immunologic trigger such as vaccination or Epstein–Barr virus infection.

Associations between the development of POTS and recent receipt of the human papillomavirus vaccine have appeared.

Overactive bladder can also be present in individuals with POTS.

Medications that may exacerbate symptoms by reducing the intravascular volume (diuretics, mineralocorticoid receptor antagonists such as drospirenone), increasing vasodilation (calcium channel blockers, α-antagonists) or increasing fatigue (β-receptor antagonists).

External factors that may contribute to symptoms, such as daily salt and water intake, sleep hygiene and physical activity, as well as anxiety and depression

The head-up tilt-table test is the gold standard for diagnosis of orthostatic dysregulation and vasovagal syncope.

The head-up tilt-table test may uncover even subtle physiologic changes, as the calf muscles contribute less to venous return when the patient is supported on a tilt table.

Baroreceptors are stretch-sensitive mechanoreceptors located in the aortic arch and carotid sinuses.

Baroreceptors monitor changes in blood pressure and provide a rapid negative feedback loop between heart rate and blood pressure.

Elevated blood pressure activates the baroreflex, leading to decreases in HR and blood pressure.

A drop in blood pressure will inhibit the baroreceptor, leading to increases in HR and blood pressure.

Baroreceptor induced changes in blood pressure are mediated by both branches of the autonomic nervous system: the parasympathetic and sympathetic systems.

Rapid barororeceptor adjustments are required for regulation of Heart rate and peripheral vascular resistance during orthostatic changes.

In individuals with reduced venous return during orthostasis, but who have intact baroreceptors, a persistent reduction in stretch of the baroreceptors results in an exaggerated tachycardia.

While supine, however, individuals with POTS generally have a normal variation in heart rate variability during inspiration and expiration as the baroreceptor responds to changes in intrathoracic pressure.

Following a Valsalva maneuver, however, the normal rebound in blood pressure is exaggerated.

Hyperadrenergic POTS may relate to an increase in norepinephrine levels or defective norepinephrine clearance.

Low angiotensin levels may exacerbate POTS.

Fluorocortisone, a synthetic aldosterone analog, is often used to address hypovolemic and orthostatic symptoms.

Nonpharmacologic strategies include: avoidance of exposure to overheating, improving venous return by activation of calf muscles and tonic muscle contraction when lightheaded, maintaining good hydration may include supplementing salt and water intake and withdrawal of medications that interfere with fluid balance.

Full-length pressure stockings can reduce POTS symptoms.

Sleeping in a seated position can reduce loss of salt and water at night in patients with autonomic failure.

An exercise program incorporating recumbent exercises may also be benecial

Exercise training increases the baroreceptor sensitivity in POTS patients and decrease the upright heart rate.

There is a lack of evidence for the use of pharmacotherapy in POTS.

Single or combination therapies directed at increasing intravascular volume, increasing peripheral vasoconstriction and controlling HR are often employed.

Fludrocortisone increases the intravascular volume.

Midodrine is useful in those with peripheral pooling.

Nonselective β2 antagonists such as low-dose propranolol may be effective for treating the elevated HR.

Therapy with intravenous saline during acute decompensation can be helpful.

There is no evidence for increased mortality.

The majority of patients experience improvements in the severity of symptoms.

Complete recovery occurs only in a minority of patients.

Diagnosis is mainly clinical utilizing history and determination of blood pressure and heart rate responses in the upright posture.

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