P-wave signal-averaged electrocardiography
P-SAECG with P-wave triggering was performed before CA using the
FCP-8800 (Fukuda Denshi, Ltd, Tokyo, Japan) with 12 standard ECG leads.
First, the skin at the electrode placement site was cleaned with alcohol
and scrubbed with a rubbing pad because the signals were of relatively
low amplitude. Subsequently, the signals from each lead were amplified
and filtered between 40 Hz and 300 Hz. A modified X, Y, and Z lead system
was used to trigger signal averaging from the P-wave. The signal was
passed through a P-wave recognition program to eliminate atrial
extrasystole, and a signal of 200 beats with an error vector magnitude
of <0.4 µV was obtained. The following two ALP parameters were
evaluated: root mean square voltage during the terminal 20 ms
(RMS20) and filtered P-wave duration (PWD).
RMS20 and PWD data were automatically calculated by the
system. Positive ALP was defined as an RMS20<2.2 µV and/or a PWD >115 ms. The standard value
was based on an analysis of 120 healthy individuals.10