Postural Orthostatic Tachycardia Syndrome

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Contents 1 Definition 2 Classification 3 Treatment 4 Prognosis 5 References

Definition

• Defined as orthostatic intolerance with standing which is relieved when becoming supine. Patients frequently complain of palpitations, lightheadedness, exercise intolerance, fatigue, near syncope and syncope.

• POTS patients typically have an increase in heart rate of 30 beats/min within 10 minutes of standing or upright tilt, or a rate that exceeds 120min/beat. It is not uncommon to have resting heart rates of 160 beats per minute while standing. Other causes should be excluded, such as medications, prolonged best rest or chronic diseases. A feature that helps distinguish POTS from pure autonomic failure (PAF) and multiple systems atrophy (MSA) is that many patients will not have orthostatic hypotension, but rather only a small drop in blood pressure or even a small increase.
• POTS must be distinguished from Inappropriate Sinus Tachycardia (IST) because their respective treatments can exagerate the symptoms of the other syndrome.

• A grading system for the severity of orthostatic intolerance is seen below.
  • Grade 0 - Normal orthostatic tolderance
  • Grade 1 - Orthostatic symptoms are infrequent and occur with increased orthostatic stress. Able to stand more than 15 minutes on most occasions. Typically has unrestricted activities of daily living.
  • Grade 2 - Orthostatic symptoms occur once a week. Symptoms develop commonly with orthostatic stress. Able to stand more than 5 minutes on most occasions.
  • Grade 3 - Orthostatic symptoms develop on most occasions. Able to stand more than 1 minute. Patient is incapacitated, often times bed bound. Syncope or near syncope is common if patient attempts to stand.

Classification

• Primary etiologies of POTS
  • Most common primary form of POTS is the partial dysautonomic (PD) form. This is felt to be secondary to a failure of the peripheral autonomic nervous system to vasoconstrict (venoconstrict) in the face of orthostatic stress. This subsequently gives rise to venous pooling in the lower extremities with a compensatory increase in heart rate and cardiac contractility. Upon standing upright, 500-700cc of blood is displaced towards the lower extremities. To compensate for this, heart rate and cardiac contractility increase. In addition, skeletal muscle tone increases and veins in the lower extremities constrict in order to propel blood upwards. Venoconstriction is depend on autonomic innervation and imbalance in this peripheral innervation is felt to be the culprit in these POTS patients.
  • There is a 5:1 female to male predominance.
  • This is felt to occur from an immune-mediated source. Many patients describe experiencing symptoms following a viral illness, surgery or pregnancy.
  • Recent studies at the Mayo Clinic have demonstrated antibodies that bind to or block acetyhcholine receptors in the peripheral autonomic ganglia.
  • Another variant of the partial dysautonomic form of POTS is the so-called "developmental" form seen in adolescents. This is seen in early teen years associated with rapid growth and appears to abate after the rapid growth spurt. This is felt to be a transient autonomic imbalance seen with growth. 80% of adolescents are asymptomatic in young adulthood.
  • The other form of primary POTS is the hyperadrenergic variant.
  • This form can be distinguished from partial dysautonomia (PD) form in that these patients will exhibit orthostatic hypertension.
  • These patients will have an exaggerated response to isoproterenol and will have significantly elevated serum norepinephrine levels (>600ng/ml).
  • These patients tend to report a gradual onset of symptoms as opposed to abrupt onset seen in the PD forms.
  • This is a genetic disorder in which a single mutation creates a dysfunctional reuptake transporter protein that clears norepinephrine from the intrasynaptic cleft and, therefore, leads to a spillover of this catecholamine in the bloodstream.
  • This can be confused with a pheochromocytoma.

• Secondary etiologies of POTS
  • Most common secondary etiology is diabetes.
  • Also occurs with sarcoid, SLE, amyloid
  • Also seen in association with joint hypermobility syndrome (JHS). Patients have hyperextensibility of joints with easy bruising, varicose veins, muscle and joint pain as well as orthostatic intolerance. Rather than autonomic imbalances, this is felt to be due to abnormal elastic connective tissue within the peripheral vasculature.
  • POTS may also present as a paraneoplastic syndrome in adenocarcinomas of the lung, breast, pancreas and ovaries.

Treatment

Treatment	Dosing	Form Effective in	Side Effects
Exercise	Aerobic exercise 3x week	PD,H	Can worsen with too vigorous exercise
Hydration	2 liters/day	PD	Edema
Salt	2-4 grams/day	PD	Edema
Fludrocortisone	0.1-.0.2mg po daily	PD	Low K, Edema
Midodrine	5-10mg po tid	PD	Hypertension, "goosebumps"
Pyridostigmine	30-60mg po bid	PD	nausea, diarrhea
SSRI	drug dependent	PD	nausea, sexual problems
methylphenidate	5-10mg po tid	PD	nausea, dependency
Erythropoietin	10,000-20,000 units SQ weekly	PD	pain at injection site
Octreotide	50-200 micrograms sq tid	PD	nausea, diarrhea
Clonidine	0.1-0.3mg po bid	H	dry mouth
Labetolol	100-200mg po tid	H	Fatigue

• PD=partial dysautonomic form, H=hyperadrenergic form

Prognosis

• Approximately 50% of primary POTS patients (post-viral) will have good recovery in 2-5 years. The younger the patient, the better the chance for a favorable outcome.
• As described, in the developmental form, approximately 80% will have good recovery in young adulthood.
• Most patients will respond to physical therapy and pharmacotherapy.
• Patients with the hyperadrenergic form generally require indefinite treatment.

References

• Grubb, Blair. The Postural Tachycardia Syndrome: A Concise Guide to Diagnosis and Management. Journal of Cardiovascular Electrophysiology. Jan. 2006, Vol. 17, No. 1. Pages 108-112