ECG measurement protocol
The Carto 3 Version 6 electrophysiological mapping system was used to
measure the parameters of the QRS morphology during sinus rhythm (SR)
and VA. The lead gain was uniform with a paper speed of 100 mm/s.
Several parameters were obtained similar to previous studies: (1) R-wave
and QRS complex amplitudes in lead V1–V3 during SR and VA,
measured
from the peak of the QRS complex to the isoelectric line and the nadir
of the QRS complex; (2) R-wave duration in leads V1–V2 during VA,
measured from the
onset
of the QRS complex to the transection point between the R-wave and
isoelectric line; (3) total QRS duration during VA, measured from the
earliest onset of the QRS complex to the time of the latest activation
in any lead; (4) the precordial transition lead was defined as the
position in which the amplitudes of the R- and S-waves were equal. The
precordial transition zone (TZ) score was defined as the lead in which
the
R/S-wave amplitude ratio was 0.9–1.1. If the ratio was
>1.1,
the
TZ score was graded in decrements of 0.5 points. On the other hand, if
it was <0.9, the TZ score was graded in increments of 0.5
points; (5) R-wave deflection interval, measured from the initiation to
the peak of the QRS complex in leads V2 and V3 during VA; and (6)
amplitude of the QRS complex within the initial 40 ms in lead V2.
The
ECG parameters[3–11] proposed to predict the origin of the VA from
the RVOT or LVOT are presented in Table 1. For all cases, quantitative
measurements were performed by two observers. If there was apparent
discordance between the two observers, Dr. Jiang was consulted. In our
validation study, all 100 patients were selected from two different
hospitals, and ECG measurements were performed by observers different
from the previous study. Calculation of the parameters and statistical
analysis were performed by the Tianjin Institute of Cardiovascular
Diseases; they were blinded to the procedure. Our study protocol was
approved by the ethics committee of the hospital. Owing to the
retrospective observational nature of the study, it was not registered
on ClinicalTrials.gov.