Background Pacemaker implantation involves intraoperative testing of ventricular sensing using a device called a pacing system analyzer (PSA). The value obtained is expected to correspond to those taken by the pacemaker after its implantation. This study determined the latency period for sensing intracardiac electrogram (EGM) by the right ventricular (RV) lead. Methods Patients without significant heart disease and underlying intrinsic atrioventricular (AV) conduction underwent Medtronic or Abbott dual‐chamber pacemaker implantation with the RV lead positioned on the mid‐septum. Real‐time sensing data were obtained through PSA and after pacemaker implantation to evaluate latency as the time interval Q‐VS between the onset of QRS on surface electrocardiogram and the sensed EGM by the RV lead. Results Of 157 patients, 105 had narrow QRS (<120 ms) and 52 had wide QRS of complete right bundle branch block (RBBB). Both narrow‐QRS and RBBB patients had longer sensing latency through PSA (50.9 ± 24.2 and 67.8 ± 32.9 ms, respectively) than through pacemaker (18.2 ± 12.8 and 31.2 ± 14.8 ms, respectively, both p < 0.001). RBBB patients had longer sensing latency compared with narrow QRS patients, either through PSA or through pacemaker (p < 0.001). The sensing latency of Medtronic recipients was longer than those of Abbott in narrow‐QRS (p < 0.05), but not in RBBB. Conclusion We demonstrated longer RV lead sensing latency (1) through PSA than through pacemaker, (2) in RBBB than in narrow‐QRS, and (3) in Medtronic pacemakers compared with Abbott pacemakers. Knowledge of sensing latency helps the optimization of the AV delay.

Funding Acknowledgements Type of funding sources: None. Introduction Pacemaker’s ventricular sensing function relies on the analysis of the intracardiac electrogram (EGM) including the timing of the intrinsic detection. The phenomenon of ventricular sensing latency refers to the gap of time by which the intrinsic signal gets delayed to be detected compared with the surface electrogram (ECG). A pacing system analyzer (PSA) unit is needed to record the EGM during pacemaker operation, which is expected to correspond to those taken following implantation. Purpose We sought to determine the latency period for sensing EGM by the right ventricular (RV) lead, either through the PSA or through the implanted pacemaker on the same patient. Methods Patients without significant heart disease and intrinsic atrioventricular conduction underwent conventional dual-chamber Medtronic or Abbott pacemaker implantation with the RV lead positioned on mid-septum. Real time sensing data was obtained through PSA and after pacemaker implantation. The RV lead sensing latency was defined as the time interval Q-VS measured from the beginning of QRS on ECG to the released ventricular sensed (VS) event marker on either device. Results Of 157 patients, 105 had narrow QRS (&lt;120 ms) and 52 had wide QRS (≥120 ms) of right bundle branch block (RBBB). Both narrow QRS and RBBB patients had longer sensing latency through PSA (50.9 ± 24.2 ms and 67.8 ± 32.9 ms, respectively) than through pacemaker (18.2 ± 12.8 ms and 31.2 ± 14.8 ms, respectively, both p&lt;0.001). RBBB patients had longer sensing latency compared with narrow QRS patients, either through PSA or through pacemaker (p&lt;0.001). The sensing latency of Medtronic recipients was longer than those of Abbott in narrow QRS, but not in RBBB (p=0.03 and p=0.08, respectively). Conclusion We demonstrated longer RV lead sensing latency (1) through PSA than through the implanted pacemaker, (2) in RBBB than in narrow QRS, (3) in Medtronic pacemakers compared with Abbott pacemakers. Knowledge of the RV lead sensing latency helps optimization of atrioventricular delay and reduces unnecessary ventricular pacing.