Cardiac Autonomic Response to Active Standing in Adults With Vasovagal Syncope.

Abstract

Little is known about the autonomic response to active standing in vasovagal syncope, and most works have focused on children or adolescents. The aim of this work was to study the changes in cardiac autonomic modulation in adult patients with vasovagal syncope through heart rate variability analysis with linear and short-term complexity (alpha-1) indexes during supine position and active standing, in patients with positive or negative head-up tilt test (HUTT). Twenty-five patients with vasovagal syncope were included. Heart rate variability linear and short-term complexity (alpha-1) indexes were recorded during an active standing test (15 minutes in each position) and compared among patients grouped by HUTT outcome and between positions. During supine position, positive HUTT (+HUTT) patients had longer mean RR (1016 [850-1051] milliseconds), higher pNN50 (17.7 [9.2-26.2]), lower sympathovagal balance (1.3 [0.5-1.7]), and alpha-1 (0.9 [0.8-1.0]) than negative HUTT (-HUTT) patients (871 [776-969] milliseconds, 8.8 [2.1-14.5], 2.9 [1.3-3.9], and 1.2 [1.0-1.1], respectively). During active standing, heart rate and alpha-1 increased in both groups; in +HUTT patients, pNN50 decreased, whereas sympathovagal balance increased. The magnitude of change between positions of sympathovagal balance and alpha-1 was 6.1 and 4.8 times larger in +HUTT than -HUTT patients, respectively. The underlying cardiac autonomic mechanism in vasovagal syncope may involve different autonomic patterns in subjects with a history of recurrent syncope and +HUTT or -HUTT.