Background
Resistance training for leg muscles is recommended for patients with postural tachycardia syndrome (POTS). However, no study has characterized the relationships between orthostatic symptoms, heart rate (HR) increase, and the mass of the lower leg muscle in patients with POTS. We sought to determine the relationships between the mass of the lower leg muscle, HR increase during the head-up tilt (HUT) test, and orthostatic symptoms in patients with POTS.
Methods
We prospectively enrolled 42 patients with POTS who were older than 16 years. The muscle mass was estimated using bioelectrical impedance analysis. We used the International Physical Activity Questionnaire-Short Form to measure self-reported physical activity. All patients were asked to complete the Korean version of the Orthostatic Grading Scale (KOGS).
Results
The HR increased during the HUT test by 38.7±7.88 beats/minutes. Both the HR increase during the HUT test and the total KOGS score were negatively correlated with the total metabolic equivalent of the task. The leg circumference and muscle mass were not correlated with the HR increase during the HUT test or the KOGS score.
Conclusions
The leg circumference and muscle mass were not related to orthostatic symptoms in patients with POTS. Cardiac remodeling or blood volume increase may be responsible for improvement in POTS after physical activity.

Orthostatic dizziness is feeling dizzy or lightheaded when standing up. Hemodynamic orthostatic dizziness can be caused by autonomic dysfunction such as orthostatic hypotension or postural tachycardia syndrome. The interpretation of the autonomic function test results in patients with orthostatic dizziness is crucial for diagnosing and managing the underlying condition. The head-up tilt and Valsalva tests are especially important for evaluating adrenergic function in patients with hemodynamic orthostatic dizziness. However, it is important to note that autonomic function tests do not cover the entire diagnostic process, since their findings need to be considered along with the detailed history and physical examination results of the patient because various differential diagnoses exist for orthostatic dizziness. Ensuring appropriate treatment by interpreting the autonomic function test results can help to determine the improvement of and prevents falls from orthostatic dizziness.

Background
Postural tachycardia syndrome (POTS) refers to the presence of orthostatic intolerance symptoms associated with a heart rate increment of greater than 30 beats/min, usually up to 120 beats/min, on head-up tilt test. Symptoms related to POTS are usually lightheadedness, palpitations and tremor, but syncope can also occur. The pathophysiology of POTS is heterogeneous and its prognosis is uncertain.
Methods
We prospectively evaluated patients who met the criteria for POTS, at baseline and follow-up, using composite autonomic symptom scores and autonomic tests to assess the autonomic function. We compared the clinical and autonomic test results between baseline and follow-up.
Results
Sixty-eight patients met the inclusion criteria for POTS and forty-five patients were ultimately followed up for at least 1 year after baseline. The patients were predominantly young females (84%), with a mean age of 21 years. Most patients showed improved orthostatic symptoms and more than a quarter of patients had no longer met the criteria for POTS at follow-up.
Conclusions
Most patients had a benign outcome in that they could resume their daily activities without great limitations. Our results demonstrated a relatively favorable prognosis in most patients with POTS.

Citations

• Long‐Term POTS Outcomes Survey: Diagnosis, Therapy, and Clinical Outcomes
  Jeffrey R. Boris, Edward C. Shadiack, Elizabeth M. McCormick, Laura MacMullen, Ibrahim George‐Sankoh, Marni J. Falk
  Journal of the American Heart Association.2024;[Epub]     CrossRef

Orthostatic intolerance is defined as the development of various symptoms during standing that are relieved by recumbency. Postural tachycardia syndrome (POTS) is another nomenclature of orthostatic intolerance. POTS characterized by a heart rate increase