Analysis of the P-wave
In all patients, the body-surface 12-lead ECG was recorded at a paper speed of 25 mm/s with a calibration of 1 mV = 10 mm and analyzed thoroughly for the calculation of the maximum P-wave amplitude, minimum P-wave amplitude, maximum P-wave duration, minimum P-wave duration, and PWD. For P-wave analysis, the most recent ECG recording of sinus rhythm recorded just prior to CIED implantation was used (Figure 2). P-wave duration and PWD were manually measured in all leads with an ECG magnifier being used to mark the P-wave onset and offset, respectively. The P-wave duration was defined as the time measured from the onset to the end of the P-wave deflection. The onset of the P-wave was considered to be the junction between the isoelectric line and the first visible upward or downward slope of the trace, while the return of the trace to its isoelectric line was considered to be the end of the P-wave. When a P-wave exhibited a biphasic form, the latter negative phase was also included in the P-wave duration (Figure 3A). The P-wave amplitude was measured as the height of the peak of positive deflection or the depth of the bottom of negative deflection from the isoelectrical line of the onset point.14–17 In the case of a biphasic P-wave, the P-wave amplitude was measured as the difference between the positive peak and negative bottom of the recording (Figure 3A). For P-wave analysis, durations and amplitudes of P-waves in leads II and V1 and the maximum P-wave duration in all 12 leads were used as the parameters of interest. Furthermore, PWD was calculated as the difference between the maximum and minimum P-wave durations in milliseconds within the same 12-channel ECG (Figure 3B).8,18