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. Methods and 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 β-adrenergic stimulation (tilt, exercise, and epinephrine and isoproterenol infusions), sequential and combined β-adrenergic and parasympathetic blockade, and α-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 μV) 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.
- QRS duration
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)