Determinants of Exercise Intolerance in Postural Orthostatic Tachycardia Syndrome: A Systematic Review

Area of Science:

• Cardiology
• Exercise Physiology
• Autonomic Dysfunction

Background:

• Postural orthostatic tachycardia syndrome (POTS) is a condition characterized by an excessive heart rate (HR) increase upon standing, often leading to symptoms like dizziness and exercise intolerance.
• The underlying mechanisms contributing to exercise intolerance in POTS remain incompletely understood, necessitating further investigation into cardiorespiratory fitness and hemodynamic responses.

Purpose of the Study:

• To conduct a systematic review of existing literature on cardiorespiratory fitness in patients with POTS.
• To explore potential determinants of exercise intolerance within the POTS population.

Main Methods:

• A systematic review was performed on original prospective and retrospective cohort studies and randomized controlled trials.
• Studies included formal exercise assessments, measuring parameters such as peak oxygen consumption (VO2) and hemodynamics (HR, stroke volume (SV), cardiac output).
• Data from 17 cohorts (1321 POTS subjects) and 502 controls were analyzed.

Main Results:

• Patients with POTS exhibited higher HR at standing and during submaximal exercise, reaching peak HR earlier compared to controls.
• Reduced peak VO2 was observed in 80% of POTS studies, but this difference diminished to 30% when accounting for deconditioning.
• While reduced SV was common (70% of studies), cardiac output was generally maintained or increased, suggesting it's not the primary cause of symptoms.

Conclusions:

• POTS patients achieve peak HR more rapidly, with increased HR associated with reduced SV, but preserved or increased cardiac output.
• The findings suggest that interventions aimed at reducing HR may enhance exercise capacity in POTS by delaying peak HR and alleviating symptoms.
• Exercise training and propranolol have demonstrated efficacy in improving peak VO2 in POTS patients.