Postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome is a poorly understood autonomic disturbance, which manifests as a change in Heart Rate>30BPM upon the patient standing erect from supine or a head-up tilt without underlying orthostatic hypotension. Sympathetic hyperstimulation secondary to a fall in vascular tone and cerebral hypoperfusion leads to transient symptoms such as inappropriate sinus tachycardia, chronic fatigue and dizziness. Many patients also report non specific symptoms such as GI disturbances and sleep disturbances. This incapacitating syndrome has no known etiology, with theories listing post infectious, autoimmune, cardiac deconditioning and emotional states as possible factors. Antinuclear antibodies along with elevated ganglionic, adrenergic, and muscarinic acetylcholine receptor antibodies have all been reported. Diagnosis involves eliminating all primary cardiac, endocrine, neuropathic and psychiatric causes of postural tachycardia. Treatment is multimodal and consists of patient education, volume replenishment, physical countermaneuvers (graded stockings) and pharmacological therapy.

POTS was not identified as a separate entity until 1982, and until then was considered as part of a larger collection known as “irritable heart” syndrome or “Da Costa syndrome” named after Jacob Da Costa. Jacob Mendes Da Costa worked at Satterlee Hospital in Philadelphia. He studied over 400 patients with non-specific cardiac complaints during the American civil war. He recognized a pattern between the patients and named the collection of symptoms “irritable heart” in 1862. By 1871 he compiled and published his results. “irritable heart” encompassed many distinct conditions including POTS and psychiatric conditions which were later separately identified. The condition was described in 1993 by Ronald Schondorf and Phillip A. Low of the Mayo Clinic.

The pathophysiology is poorly understood and multifactorial. There are many reported findings across patients with POTS, which are interlinked and present in a variety of combinations, making it difficult to pinpoint one as primary and thereby causative. Evidence suggests that the etiology involves:

• Distal denervation with preservation of cardiac innervation. Studies have shown reduced response to stimulation in the lower limbs in patients with POTS. This is thought to be due to a neuropathy arising post infection, however there is also evidence of autoantibodies against the ganglionic acetylcholine receptor, lending support for an autoimmune origin of the disease.
• Hypovolemia or possible increased baroreceptor sensitivity. The most significant finding to lead to this theory is the symptomatic relief experienced by patients after infusion of saline, along with findings that suggest a predisposition to volume constriction in these patients. Conversely, constant and prolonged sympathetic activation could cause a mild reduction in circulating volume.
• abnormal venous function causing decreased preload on standing. Evidence of venous pooling and therefore reduced venous return has been reported in some studies, along with the reduction of symptoms with the use of compression trousers. This could be due to the denervation of the distal limbs or the increased release of vasodilators.
• cardiovasclar deconditioning
• hyperadrenergic state (increase in sympathetic activity)
• Post infectious etiology.
• genetic factors
  

POTS is believed to be the most prevalent type of orthostatic intolerance. One study approximates the prevalence to be 500,000 americans. It is also commonly seen in younger patients (<45 years) who present to autonomic dysfunction clinics. Women are more likely to suffer from this disorder, with the ratio between genders being 4-5:1. The cause of this is unknown as yet. There is no racial predilection to this disorder.

There are no clear risk factors for POTS, however a small minority of patients with the condition have been noted to have a mutated norepinephrine transporter gene. There is increasing evidence of association between POTS and joint hypermobility disorders such as Ehlers-Danlos syndrome. POTS may develop after a viral illness such as mononucleosis, and is also reported to develop after illnesses requiring prolonged hospitalisation and immobility. Patients suffering from celiac disease and Sjogrens syndrome may be at higher risk for developing POTS as well.

Most patients present young, and prognosis is generally favourable.

History and Symptoms | Physical Examination | Laboratory Findings | Electrocardiogram | Chest X Ray | Echocardiography | Other Diagnostic Studies

ACC/AHA/ESC Treatment Guidelines | Medical Therapy | Cost-Effectiveness of Therapy | Future or Investigational Therapies

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