Evaluating and managing postural tachycardia syndrome

DIAGNOSTIC STRATEGY

A patient presenting with symptoms suggestive of POTS should first undergo a detailed history and physical examination. Other causes of sinus tachycardia should be considered. 

Detailed history, symptom review

The history should focus on determining symptom burden, including tachycardia onset, frequency, severity, and triggers; the presence of syncope; and the impact of symptoms on daily function and quality of life.

POTS-associated orthostatic intolerance manifests with cardiac and noncardiac symptoms (Table 1).

,

Presyncope and its associated symptoms occur in less than one-third of patients with POTS, and syncope is not a principal feature.⁴ If syncope is the predominant complaint, alternative causes should be investigated. The usual cause of syncope in the general population is thought to be vasovagal.

In addition to orthostatic intolerance, gastrointestinal disturbances are common in POTS, presenting as abdominal pain, heartburn, irregular bowel movements, diarrhea, or constipation. Symptoms of gastroparesis are less common. Gastrointestinal symptoms tend to be prolonged, lasting hours and occurring multiple times a week. They tend not to improve in the supine position.³⁵ 

POTS-associated symptoms may develop insidiously, but patients often report onset after an acute stressor such as pregnancy, major surgery, or a presumed viral illness.⁴ Whether these putative triggers are causative or coincidental is unknown. Symptoms of orthostatic intolerance tend to be exacerbated by dehydration, heat, alcohol, exercise, and menstruation.^36,37

Consider the family history: 1 in 8 patients with POTS reports familial orthostatic intolerance,³⁸ suggesting a genetic role in some patients. Inquire about symptoms or a previous diagnosis of Ehlers-Danlos syndrome and mast cell activation syndrome.

Consider other conditions

Other causes of orthostatic tachycardia are listed in Table 2.^39–41 Most can be diagnosed with a careful history, physical examination, and laboratory tests. Two of the more challenging diagnoses are described below. 

Pheochromocytoma causes hyperadrenergic symptoms (eg, palpitations, lightheadedness) like those in POTS, but patients with pheochromocytoma typically have these symptoms while supine. Pheochromocytoma is also characterized by plasma norepinephrine levels much higher than in POTS.⁴ Plasma metanephrine testing helps diagnose or rule out pheochromocytoma.⁵

Inappropriate sinus tachycardia, like pheochromocytoma, also has clinical features similar to those of POTS, as well as tachycardia present when supine. It involves higher sympathetic tone and lower parasympathetic tone compared with POTS; patients commonly have a daytime resting heart rate of at least 100 bpm or a 24-hour mean heart rate of at least 90 bpm.^1,42 While the intrinsic heart rate is heightened in inappropriate sinus tachycardia, it is not different between POTS patients and healthy individuals.^42,43 Distinguishing POTS from inappropriate sinus tachycardia is further complicated by the broad inclusion criteria of most studies of inappropriate sinus tachycardia, which failed to exclude patients with POTS.⁴⁴ The Heart Rhythm Society recently adopted distinct definitions for the 2 conditions.¹

Physical examination: Focus on vital signs

The most critical component of the physical examination is thorough measurement of orthostatic vital signs (Figure 1). Blood pressure and heart rate should be measured while the patient has been supine for at least 5 minutes, and again after being upright for 1, 3, 5, and 10 minutes. These measurements determine if orthostatic hypotension is present and whether the patient meets the heart rate criteria for POTS. Patients with POTS tend to experience greater orthostatic tachycardia in the morning, so evaluation early in the day optimizes diagnostic sensitivity.⁵

Dependent acrocyanosis—dark red-blue discoloration of the lower legs that is cold to the touch—occurs in about half of patients with POTS upon standing.⁴ Dependent acrocyanosis is associated with joint hypermobility and Ehlers-Danlos syndrome, so these conditions should also be considered if findings are positive.

Laboratory testing for other causes

Laboratory testing is used mainly to detect primary causes of sinus tachycardia. Tests should include:

• Complete blood cell count with hematocrit (for severe anemia)
• Thyroid-stimulating hormone level (for hyperthyroidism)
• Electrolyte panel (for significant electrolyte disturbances).

Evidence is insufficient to support routinely measuring the vitamin B₁₂ level, iron indices, and serum markers for celiac disease, although these may be done if the history or physical examination suggests related problems.⁴ Sicca symptoms (severe dry eye or dry mouth) should trigger evaluation for Sjögren syndrome.

Electrocardiography needed

Electrocardiography should be performed to investigate for cardiac conduction abnormalities as well as for resting markers of a supraventricular tachyarrhythmia. Extended ambulatory (Holter) monitoring may be useful to evaluate for a transient reentrant tachyarrhythmia⁴; however, it does not record body position, so it can be difficult to determine if detected episodes of tachycardia are related to posture.

Additional testing for select cases

Further investigation is usually not needed to diagnose POTS but should be considered in some cases. Advanced tests are typically performed at a tertiary care referral center and include: 


• Quantitative sensory testing to evaluate for small-fiber neuropathy (ie, Quantitative Sudomotor Axon Reflex Test, or QSART), which occurs in the neuropathic POTS subtype
• Formal autonomic function testing to characterize neurovascular responsiveness  
• Supine and standing plasma norepinephrine levels (fractionated catecholamines) to characterize the net activation of the sympathetic nervous system
• Blood volume assessments to assess hypovolemia 
• Formal exercise testing to objectively quantify exercise capacity.