Jj. Goldberger et al., ASSESSMENT OF EFFECTS OF AUTONOMIC STIMULATION AND BLOCKADE ON THE SIGNAL-AVERAGED ELECTROCARDIOGRAM, Circulation, 89(4), 1994, pp. 1656-1664
Background Signal-averaged ECG is a noninvasive test designed to detec
t ''late potentials.'' The effects of alterations in autonomic tone on
the signal-averaged ECG have not been evaluated systematically. Metho
ds and Results The effects of autonomic stimulation and blockade on th
e 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-averag
ed ECG was recorded at baseline and after physiological and pharmacolo
gic beta-adrenergic stimulation (tilt, exercise, and epinephrine and i
soproterenol infusions), sequential and combined beta-adrenergic and p
arasympathetic blockade, and alpha-adrenergic stimulation before and a
fter parasympathetic blockade. Analysis was performed with a bidirecti
onal filter (40-Hz high-pass). Significant changes in the signal-avera
ged 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 isop
roterenol (99.6+/-12.6 milliseconds). Changes in the root-mean-square
voltage of the terminal 40 milliseconds and the low-amplitude (<40 mu
V) signal duration paralleled the changes in the QRS duration. Conclus
ions The signal-averaged ECG does not measure only ''fixed'' parameter
s but rather is altered under a variety of physiological and pharmacol
ogic conditions. Upright tilt leads to shortening of the QRS duration
before and after autonomic blockade; thus, the decrease in QRS duratio
n with tilt may be related to factors other than changes in autonomic
tone. These findings have implications for interpretation of the resul
ts of signal-averaged ECG.