title: Effects of upright posture on filtered QRS parameter of the signal-averaged electrocardiogram in healthy volunteers.
abstract: The effects of upright posture on signal-averaged electrocardiography were studied together with short-term spectral analysis of heart rate variability (HRV) in 20 healthy volunteers (mean age 34 +/- 10 years). Filtered QRS duration from 5-minute epochs and corresponding spectral measures of HRV were computed from digital ambulatory electrocardiographic recordings both at supine rest and during upright tilt (60 degrees). Upright tilt was associated with a significant shortening of filtered QRS (88.2 +/- 8 vs 82.6 +/- 8 msec, p < 0.0001) and with an increase in its maximum amplitude (78.8 +/- 39 vs 87 +/- 48 microV, p < 0.004), whereas the average noise level remained unchanged. In the same time the ratio between low- and high-frequency components of HRV shifted in favor of sympathetic predominance (1.4 +/- 1.2 vs 3.4 +/- 2.9, p < 0.003). No correlation was found between changes in signal-averaged electrocardiography and HRV parameters associated with upright tilt. These data suggest that upright tilt-induced shortening in filtered QRS duration is rather vector-related and does not reflect changes in cardiac autonomic tone. This result must be considered when dynamic analysis of signal-averaged electrocardiography is attempted.
authors.affiliation: Department of Cardiological Sciences, St George's Hospital Medical School, London, UK.
authors.forename: J
authors.initials: J
authors.lastname: Kautzner
authors.forename: J E
authors.initials: JE
authors.lastname: Hartikainen
authors.forename: A J
authors.initials: AJ
authors.lastname: Camm
authors.forename: M
authors.initials: M
authors.lastname: Malik
mesh_terms: D000328:Adult; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D011187:Posture; D012815:Signal Processing, Computer-Assisted