2.4 Electrocardiographic measurements
Baseline patient characteristics were collected retrospectively. The
surface electrogram was recorded by the GE CardioLab Electrophysiology
recording system (GEHealthcare Inc, Marlborough, MA) at 100 mm/s. We
measured two parameters, which are the intrinsic QRS duration (iQRSd)
and the paced QRS duration (pQRSd). The iQRSd was defined from the first
deviation from isoelectric line to the last deviation of the QRS complex
in the 12 leads. The pQRSd was measured - for SLBBP - from the onset of
the first sharp vector of the QRS complexes crossing the baseline and -
for NSLBBP - from the onset of the sharpest deflection to the end of the
last deflection of the complex in the 12 leads, respectively. All two of
these parameters were measured by Cardio Calipers 3.3 (Inconico, Inc,
New York, NY). Three continuous QRS complexes on the lead V1 were
measured and the averaged values were reported. The electrocardiographic
recording and measurements were performed and analyzed by two
independent and experienced ECG specialists.