Postural tachycardia syndrome (PoTS)

Introduction
Postural Tachycardia Syndrome (PoTS) is a form of autonomic dysfunction characterized by an excessive increase in heart rate upon standing, in the absence of orthostatic hypotension. It leads to symptoms of cerebral hypoperfusion and sympathetic overactivity, such as dizziness, palpitations, and fatigue. PoTS is a chronic condition that can significantly affect quality of life but is not typically life-threatening.

---

Epidemiology

• Predominantly affects women (about 4:1 female-to-male ratio).

• Most commonly presents between ages 15–50 years.

• Estimated prevalence: ~0.2–1% of the population.

• Often underdiagnosed due to overlap with anxiety, chronic fatigue syndrome, and other disorders.

---

Pathophysiology
The underlying mechanism of PoTS involves autonomic nervous system imbalance, with excessive sympathetic activation upon standing. Several pathophysiological subtypes exist:

• Neuropathic PoTS: Partial autonomic denervation, especially in lower limbs, leading to impaired vasoconstriction and excessive venous pooling.

• Hyperadrenergic PoTS: Increased sympathetic tone with high plasma norepinephrine upon standing.

• Hypovolemic PoTS: Reduced circulating blood volume.

• Secondary PoTS: Due to another condition, such as Ehlers–Danlos syndrome, diabetes, autoimmune disorders, or post-viral autonomic dysfunction.

The hallmark is a marked increase in heart rate (≥30 bpm in adults; ≥40 bpm in adolescents) within 10 minutes of standing, without significant drop in blood pressure.

---

Diagnostic Criteria
According to consensus statements, diagnosis requires:

1. Sustained heart rate increase:

   • ≥30 bpm (adults) or ≥40 bpm (ages 12–19) within 10 minutes of standing or head-up tilt.

2. No orthostatic hypotension:

   • Systolic BP drop <20 mmHg and diastolic BP drop <10 mmHg.

3. Symptoms of orthostatic intolerance: Present for ≥6 months and relieved by recumbency.

4. Exclusion of other causes (e.g., dehydration, anemia, hyperthyroidism).

---

Clinical Features

Orthostatic Symptoms:

• Palpitations

• Lightheadedness or dizziness

• Near-syncope or syncope

• Visual blurring/tunnel vision

• Headache

Non-orthostatic Symptoms (due to sympathetic overactivity or comorbid conditions):

• Fatigue

• Exercise intolerance

• Tremulousness

• Sweating

• Nausea, abdominal pain

• “Brain fog” (cognitive difficulties)

---

Triggers and Aggravating Factors

• Prolonged standing

• Heat exposure

• Dehydration

• Alcohol

• Large carbohydrate-rich meals

• Menstrual cycle hormonal fluctuations

---

Associated Conditions

• Ehlers–Danlos syndrome (hypermobility type)

• Mast cell activation syndrome

• Chronic fatigue syndrome/myalgic encephalomyelitis

• Autoimmune diseases

• Post-viral syndromes (including post-COVID-19)

---

Investigations

Bedside:

• Active stand test or 10-minute standing test: HR and BP measured supine and during standing.

Laboratory:

• CBC, thyroid function, ferritin, electrolytes, renal and liver function, fasting glucose.

• Morning cortisol (if adrenal insufficiency suspected).

Specialized tests:

• Tilt table test (gold standard for diagnosis).

• Plasma catecholamines (supine and standing) to identify hyperadrenergic subtype.

• Autonomic reflex testing (QSART, Valsalva).

---

Management
PoTS treatment is multimodal, focusing on symptom relief, improvement of daily functioning, and management of underlying causes.

1. Non-Pharmacological Measures (First-Line for All Patients)

• Volume expansion:

  • Fluid intake: ~2–3 L/day.

  • Salt intake: ~8–10 g/day (unless contraindicated).

• Compression garments: Waist-high compression stockings or abdominal binders to reduce venous pooling.

• Exercise reconditioning: Gradual, structured aerobic and resistance training, starting with recumbent exercises (rowing, recumbent cycling) and progressing to upright.

• Postural adjustments:

  • Avoid prolonged standing.

  • Cross legs or contract calf muscles while standing.

  • Rise slowly from lying to standing.

• Avoid triggers: Heat, alcohol, large meals, dehydration.

---

2. Pharmacological Treatment
Considered for persistent, disabling symptoms despite optimal non-drug measures. Medication choice is guided by PoTS subtype and patient profile.

• Volume expansion agents:

  • Fludrocortisone acetate: 0.05–0.2 mg orally once daily; increases sodium and water retention. Monitor BP, potassium.

• Vasoconstrictors:

  • Midodrine: 2.5–10 mg orally three times daily (last dose at least 4 hours before bedtime to avoid supine hypertension).

• Heart rate control:

  • Beta-blockers (e.g., propranolol 10–20 mg orally up to 4 times daily; bisoprolol 2.5–5 mg once daily). Low doses may reduce tachycardia without excessive fatigue.

  • Ivabradine: 2.5–5 mg orally twice daily; selectively inhibits If current in the sinoatrial node, lowering HR without affecting BP.

• Central sympatholytics (for hyperadrenergic PoTS):

  • Clonidine: 0.1 mg orally twice daily or transdermal patch.

  • Methyldopa: 125–250 mg orally twice daily.

• Cholinesterase inhibitors:

  • Pyridostigmine: 30–60 mg orally two to three times daily; enhances parasympathetic activity, improving autonomic balance.

---

3. Management of Associated Conditions

• Treat comorbidities such as Ehlers–Danlos syndrome, mast cell activation, and iron deficiency.

• Address psychological impact with supportive counseling if needed.

---

Prognosis

• Course is variable: Some patients experience gradual improvement over 1–3 years, especially with early diagnosis and lifestyle modification.

• Others may have persistent symptoms requiring long-term management.

• PoTS does not usually shorten life expectancy but can cause significant disability.