Inadequate sympathovagal balance in response to orthostatism in patients with unexplained syncope and a positive head up tilt test

Abstract

Aim-To analyse the immediate response of heart rate variability (HRV) in response to orthostatic stress in unexplained syncope. Subjects-69 subjects, mean (SD) age 42 (18) years, undergoing 60°head up tilt to evaluate unexplained syncope. Methods-Based on 256 second ECG samples obtained during supine and upright phases, spectral analyses of low (LF) and high frequency (HF) bands were calculated, as well as the LF/HF power ratio, reflecting the sympathovagal balance. All variables were measured just before tilt during the last five minutes of the supine position, during the first five minutes of head up tilt, and just before the end of passive tilt. Results-Symptoms occurred in 42 subjects (vasovagal syncope in 37; psychogenic syncope in five). Resting haemodynamics and HRV indices were similar in subjects with and without syncope. Immediately after assuming the upright posture, adaptation to orthostatism diVered between the two groups in that the LF/HF power ratio decreased by 11% from supine (from 2.7 (1.5) to 2.4 (1.2)) in the positive test group, while it increased by 11.5% (from 2.8 (1.5) to 3.1 (1.7)) in the negative test group (p = 0.02). This was because subjects with a positive test did not have the same increment in LF power with tilting as those with a negative test (11% v 28%, p = 0.04), while HF power did not alter. A decreased LF/HF power ratio persisted throughout head up tilt and was the only variable found to discriminate between subjects with positive and negative test results (p = 0.005, multivariate analysis). During the first five minutes of tilt, a decreased LF/HF power ratio occurred in 33 of 37 subjects in the positive group and three of 27 in the negative group. Thus a decreased LF/HF ratio had 89% sensitivity, 89% specificity, a 92% positive predictive value, and an 86% negative predictive value. Conclusions-Through the LF/HF power ratio, spectral analysis of HRV was highly correlated with head up tilt results. Subjects developing syncope late during continued head up tilt have a decrease in LF/HF ratio immediately after assuming the upright posture, implying that although symptoms have not developed the vasovagal reaction may already have begun. This emphasises the major role of the autonomic nervous system in the genesis of vasovagal (neurally mediated) syncope. (Heart 1999;82:312-318)

Entropy Measures in the Assessment of Heart Rate Variability in Patients with Cardiodepressive Vasovagal Syncope

“…In turn, Kouakam et al [14] have not found differences between the above groups regarding spectral HRV parameters assessed in baseline recordings. In the present paper, we focus on the cardiodepressive-type of syncope as a result of HUTT and compare it with the negative reaction to the test.…”

Shortened Head-Up Tilting Test Guided by Systolic Pressure Reductions in Neurocardiogenic Syncope

“…Since Lewis and O'Toole's report, 3 autonomic nervous system has been recognized to have a relevant role. 4 Abnormal heart rate control was demonstrated to be predictive of tilt-induced syncope; 5,6 however, what characterizes all neurocardiogenic syncope, regardless of heart rate changes, is a reduction in arterial pressure that may be the consequence of maladaptive arterial pressure control mechanisms. 7 If these abnormalities are already operative during the first asymptomatic phase of tilting, the related changes in blood pressure may characterize subjects with a positive test.…”

Altered Autonomic Balance in Normal Tension Glaucoma

“…Kouakam et al who analyzed the HRV response to orthostatic stress in patients with unexplained syncope during 60° HUT and observed LF/HF ratio was correlated with HUT. Since LF (nu) the marker of sympathetic activity, HF (nu) the marker of parasympathetic activity, therefore, during HUT significant less increase in LF band variables and less value of HF variables in glaucoma patients indicated less increase in sympathetic activity as well as decrease in parasympathetic activity [15].…”