Pseudofusion in a dual chamber pacemaker: Is this pacemaker working properly?

A 57-year-old womanwith a history of dizziness due to episodes of complete heart block and bradycardia was referred to the electrophysiology ward for pacemaker implantation. A dual chamber pacemaker (Medtronic, Relia, Medtronic, Minneapolis, USA) was implanted. Its analysis showed normal function (atrial lead capture threshold 0.5 V at 0.4 ms, ventricular lead capture threshold 0.75 V at 0.4 ms, and P-wave and R wave amplitude sensing 2 mV and 8mV, respectively). The pacemaker was programmed in the DDDR mode with a lower rate limit of 60 bpm, atrial and ventricular output of 3.5 V and 3.5 V at 0.4 ms respectively, atrial and ventricular sensitivity of 0.5 mV and 2.8 mV respectively, a paced atrioventricular interval (pAVI) of 180 ms, and a sensed atrioventricular interval of 150 ms. The post atrioventricular blanking period (PAVBP) was 60 ms. In the first day after implantation, 12-lead electrocardiography showed episodes of pseudofusion, leading to suspicion of pacemaker malfunction (Fig. 1).