Skin sympathetic nerve activity in patients with chronic orthostatic intolerance.

Abstract

Chronic orthostatic intolerance (OI) is characterizedby the development of tachycardia and other symptomswhen assuming an upright body position. The purpose of this study was to test the hypothesis that skin sympathetic nerve activity (SKNA) bursts are specific symptomatic biomarkers in patients with chronic OI. We used an electrocardiogram monitor with a built-in triaxial accelerometer to simultaneously record SKNA and posture in ambulatory participants. Study 1 compared chronic OI (14 women and 2 men; mean age 35 ± 10 years) with reference control participants (14 women; mean age 31 ± 6 years). Study 2 included 17 participants with chronic OI (15 women and 2 men; mean age 39 ± 12 years) not yet treated with ivabradine, pyridostigmine, or β-blockers. In study 1, there were 124 episodes (8 ± 4 per participant) of postural changes, with 11 episodes (8.9%) associated with symptoms. In comparison, 0 of 104 postural changes (7 ± 3 per participant) in controls were symptomatic (P = .0011). In participants with chronic OI, the SKNA bursts associated with symptomshad higher burst frequencies, longer burst durations, and larger mean burst areas than did bursts during asymptomatic periods. However, SKNA bursts and tachycardia were asymptomaticin controls. We analyzed 110 symptomatic episodes in study 2 (6 ± 5 per participant). Among them, 98 (89.1%) followed at least 1 SKNA burst. In comparison, only 41 (37.3%) had heart rate exceed 100 beats/min 1 minute before symptom onset (P < .0001). SKNA bursts are a highly specific, albeit insensitive, symptomatic biomarker for chronic OI.