2.1 P-wave measurements
The surface 12-lead ECG (TraceMasterVue®, Philips) obtained just before and immediately after implantation (filtered at 0.05-150 Hz, 10 mm/mV, 25 mm/s) were analyzed, and the sinus and paced P-waves at 60 bpm were measured with digital calipers with quadruple magnification (Figure 1). Sinus P-wave onset was defined as the point of initial upward or downward deflection from the baseline and the offset as the return of the waveform to the initial baseline. Paced P-wave onset was defined as the point of the stimulus artifact visualization. Some examples are represented in Figure 2. IAB in the sinus P-wave was defined as partial when the P-wave duration was ≥120 ms, and advanced when the duration was ≥120 ms and presented a biphasic pattern in the inferior leads. All measurements were performed by two expert cardiologists blinded to baseline patient characteristics. The study protocol was approved by the ethics committee of our institution and conforms to the ethical guidelines of the 1975 Declaration of Helsinki.