Assessment of effects of autonomic stimulation and blockade on the signal-averaged electrocardiogram.
BACKGROUND
Signal-averaged ECG is a noninvasive test designed to detect "late potentials." The effects of alterations in autonomic tone on the signal-averaged ECG have not been evaluated systematically.


RESULTS
The effects of autonomic stimulation and blockade on the signal-averaged ECG were evaluated in 14 healthy subjects (8 men and 6 women; age, 28.5 +/- 4.8 years) on 2 separate days. The signal-averaged ECG was recorded at baseline and after physiological and pharmacologic beta-adrenergic stimulation (tilt, exercise, and epinephrine and isoproterenol infusions), sequential and combined beta-adrenergic and parasympathetic blockade, and alpha-adrenergic stimulation before and after parasympathetic blockade. Analysis was performed with a bidirectional filter (40-Hz high-pass). Significant changes in the signal-averaged QRS duration from baseline (105.1 +/- 12.0 milliseconds) were noted with tilt (96.8 +/- 8.8 milliseconds), tilt after double blockade (97.5 +/- 9.0 milliseconds), epinephrine (110.5 +/- 11.8 milliseconds), and isoproterenol (99.6 +/- 12.6 milliseconds). Changes in the root-mean-square voltage of the terminal 40 milliseconds and the low-amplitude (< 40 microV) signal duration paralleled the changes in the QRS duration.


CONCLUSIONS
The signal-averaged ECG does not measure only "fixed" parameters but rather is altered under a variety of physiological and pharmacologic conditions. Upright tilt leads to shortening of the QRS duration before and after autonomic blockade; thus, the decrease in QRS duration with tilt may be related to factors other than changes in autonomic tone. These findings have implications for interpretation of the results of signal-averaged ECG.
Goldberger
J J
JJ
Department of Medicine, Northwestern University, Chicago, Ill.
Ahmed
M W
MW
Parker
M A
MA
Kadish
A H
AH
D000328:Adult; D001285:Atropine; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology*; D004562:Electrocardiography / Q000379:methods*; D004837:Epinephrine; D005080:Exercise Test; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007545:Isoproterenol; D008297:Male; D010656:Phenylephrine; D011187:Posture / Q000502:physiology; D011433:Propranolol; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted
D010656:Phenylephrine; D001285:Atropine; D011433:Propranolol; D007545:Isoproterenol; D004837:Epinephrine