The pacing spikes in this figure occur at exactly 60bpm (the baseline rate), with all spikes showing ventricular undersensing and non-capture. This should not be confused withnon-pacing, which refers to the lack of delivery of a pacing spike where one is expected. This beat could be interpreted as normal device function with pseudofusion, as the spike occurs almost simultaneously with the QRS complex. With pseudofusion, the pacing spike occurs at, or shortly after, QRS onset, but before the depolarization wavefront has reached the lead dipole. The pacing spike occurs during the myocardial refractory period and therefore does not capture the ventricle. The ventricular spike occurs on the T-wave which may be potentially pro-arrhythmic, but this is not the case here, as there is no capture.
