Impaired Endothelial Function in Patients With Postural Tachycardia Syndrome

Abstract

The purpose of this study is to evaluate endothelial function in postural tachycardia syndrome (PoTS), a poorly understood chronic condition characterized by a state of consistent orthostatic tachycardia (delta heart rate ≥30 beats per minute) upon standing without orthostatic hypotension. Nineteen patients with PoTS and 9 healthy controls were studied after 3 days of a fixed, caffeine-free, normal sodium (150 milliequivalents/day) diet. All participants underwent autonomic function testing, including sinus arrhythmia, valsalva maneuver, hyperventilation, cold pressor, handgrip, and a standing test with catecholamine measurements, followed by endothelial function testing. We analyzed 3 measures of endothelial function: percent brachial flow-mediated dilation, digital pulsatile arterial tonometry, and postischemic percent leg blood flow. Flow-mediated dilation was significantly lower in patients with PoTS (6.23±3.54% for PoTS) than in healthy controls (10.6±4.37% for controls versus, P=0.014). PoTS and controls had similar digital pulsatile arterial tonometry (1.93±0.40 arbitrary units for controls versus 2.13±0.63 arbitrary units for PoTS). PoTS had similar but suggestive percent leg blood flow to controls (313±158% for PoTS versus 468±236% for controls, P=0.098). Patients with PoTS have significantly reduced flow-mediated dilation compared with healthy controls, suggesting that PoTS is characterized by endothelial dysfunction in conduit arteries. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01308099.

Keywords: blood; heart rate; nitric oxide; syndrome; tachycardia.

Fig. 1

Panel A shows Norepinephrine (NE) values for PoTS (circles) and controls (HC, squares) during supine (open) and standing (Up, closed). Panel B shows heart rate (HR) values for PoTS (circles) and controls (HC, squares) during supine (open) and standing (closed). *, p value for the difference between supine and standing; ǂ, p value for the difference at standing between PoTS and controls.

Fig. 2

Panel A shows differences in percent flow mediated dilation (FMD) between PoTS (open circles) and controls (HC, closed squares). Panel B shows differences in percent leg blood flow (%LBF) between PoTS (open circles) and controls (HC, closed squares). Panel C shows differences in reactive hyperemic index (RHI) between PoTS (open circles) and controls (HC, closed squares). Dotted line at 1.67 indicates the cut-off value for endothelial dysfunction. *, p value for the difference between PoTS and controls.