Autonomic Determinants of POTS - Pilot1

Overview

Postural tachycardia syndrome (POTS) is a relatively common condition affecting mostly otherwise healthy young women. It is the cause of significant disability and an impairment in quality of life. These patients have high heart rate and symptoms during standing. Many of these patients are disabled and have a poor quality of life. The sympathetic nerves are part of the nervous system that helps to maintain normal blood pressures and heart rates during activities of daily life. The purpose of this study is to determine the importance of sympathetic activation as a cause of orthostatic symptoms. The investigators will assess the effects of a blood pressure medication (Moxonidine) on the symptoms during standing. Moxonidine lowers sympathetic activity. The investigators believe patients with high resting sympathetic activity might benefit from Moxonidine. It might reduce high heart rate and improve symptoms during standing. This study should help clinicians and the growing population of patients with POTS gain a better understanding of this disorder and find more personalized treatment.

Postural tachycardia syndrome (POTS) is a relatively common condition affecting mostly otherwise healthy young women. It is the cause of significant disability and an impairment in quality of life of a magnitude comparable to patients with chronic obstructive pulmonary disease or congestive heart failure. It is characterized by sympathetic activation with an exaggerated orthostatic tachycardia that responds to low doses of beta-blockers. The underlying pathophysiology of this disorder and the nature of this sympathetic activation is not clear and is likely heterogeneous. In many patients this sympathetic activation could be an appropriate compensatory response to hypovolemia, deconditioning or partial neuropathy. The investigators have identified a subset of patients in whom sympathetic activation appears to be a primary phenomenon. These patients are characterized by high central sympathetic outflow, as determined by muscle sympathetic nerve activity (MSNA) above the upper 95% confidence interval for the group. This "hyperadrenergic" phenotype is associated with a paradoxical increase in blood pressure on standing and exaggerated pressor response to the vasoconstrictive phase of the Valsalva maneuver, and clinical observations suggest they improve clinically when treated with central sympatholytics. The investigators propose to test the hypothesis that there is a subset of POTS patients with a central sympathetic activation as the primary pathophysiology. In an acute double blind, placebo-controlled, randomized study, the investigators propose that administration of the central sympatholytic moxonidine will improve orthostatic symptoms and abnormalities in orthostatic hemodynamics, as well as sympathetic outflow.