A double-blind, placebo-controlled, crossover study of the vascular effects of midodrine in neuropathic versus hyperadrenergic Postural Tachycardia Syndrome

Postural tachycardia syndrome (POTS) is a chronic form of orthostatic intolerance. Neuropathic POTS is characterized by decreased adrenergic vasoconstriction, while hyperadrenergic POTS exhibits increased adrenergic vasoconstriction. We hypothesized that midodrine, an α1-adrenergic receptor agonist, would increase calf vascular resistance (CVR), decrease calf venous capacitance (Cv), and decrease orthostatic tachycardia in neuropathic POTS but not alter hemodynamics in hyperadrenergic POTS. 20 POTS patients (12 neuropathic, 8 hyperadrenergic), ages 12-20, participated in this randomized, placebo-controlled, double-blind, crossover study. Fifteen of the subjects were female. POTS subjects received 2 weeks of treatment with midodrine or placebo, with increased dosing from 2.5mg to 10mg TID. Following a 7-day drug washout period, subjects received the crossover treatment. Heart rate (HR), mean arterial pressure (MAP), calf blood flow (Qcalf), and CVR were measured supine and during 35° head-up tilt (HUT). Cv was measured supine. In neuropathic POTS, midodrine decreased supine HR, Qcalf, Cv, while increasing MAP and R compared to placebo. During HUT, in neuropathic POTS, midodrine decreased HR, Qcalf, and Cv, while increasing MAP and CVR. In hyperadrenergic POTS, placebo and midodrine both decreased upright HR and increased supine CVR. Placebo also increased supine Cv, compared to midodrine in hyperadrenergic POTS. Therefore, midodrine improved postural tachycardia ...
Source: Clinical Science - Category: Biomedical Science Authors: Source Type: research