Impaired Endothelial Function in Patients With Postural Tachycardia Syndrome

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.