Abstract 115: Primary Hyperadrenergic Postural Tachycardia Syndrome. Evidence From Sympathetic Nerve Recordings

Abstract

Postural tachycardia syndrome (POTS) is a chronic disabling condition with excessive upright tachycardia and symptoms due to enhanced sympathetic activity in otherwise healthy young individuals. Because it is not clear if sympathetic activation is a primary phenomenon, or an appropriate compensatory response to hypovolemia, deconditioning or partial neuropathy, we analyzed resting supine muscle sympathetic nerve activity (MSNA) in 38 female POTS patients (mean±SD, age 32.1±9.1, BMI 22.7±5.4). MSNA showed a wide range of burst rate (19.7±12.1 bursts/min, range 1.2 to 54, 95% CI: 15.7 to 23.6). We compared the 1 st and 4 th Quartiles of 28 MSNA records (MSNA_Q1: < 7.3; MSNA_Q4: > 23.4 bursts/min) to determine if resting MSNA is related to heart rate (HR) or blood pressure (BP) responses to orthostatic challenge and the Valsalva maneuver (2-way ANOVA with post-hoc tests). Upright HR was inappropriately high in both groups (MSNA_Q1: 120±19 vs. MSNA_Q4: 110±20 bpm, NS), but the MSNA_Q4 group had higher upright diastolic BP than MSNA_Q1 (81±12 vs. 62±8 mmHg, P<0.01). Similarly, there were no differences in HR response to the Valsalva maneuver between groups, but systolic and diastolic BP were higher during late phase 2 in MSNA_Q4 (p<0.05), and this was preceded by higher MSNA spike rate (44.3±16.3 vs. 81.2 ±25 maximal spikes/secs per beat, p<0.01) during early phase 2 of Valsalva maneuver. The greater BP responses, but comparable HR responses, to posture and Valsalva challenges provide evidence that the subset of POTS patients with higher resting MSNA have a primary sympathetic activation. These patients might benefit from sympatholytic therapy in contrast to other POTS patients with low or absent resting MSNA.