What causes the pseudodelta wave in pacing?

The pseudodelta wave in pacing is specifically caused by the simultaneous capture of both the target myocardial tissue and the surrounding myocardium. This phenomenon occurs when the pacing electrode stimulates not only the intended area (typically the ventricles, in the case of ventricular pacing) but also nearby myocardial fibers. When these adjacent fibers are activated alongside the target fibers, it produces a distinctive morphology seen on the electrocardiogram, characterized by an additional wave component resembling a delta wave.

This situation can arise in various pacing scenarios but is particularly evident during instances where the pacing threshold is sufficient to reach beyond the desired capture zone to include adjacent tissues. It is important to note that this is not a result of pacemaker malfunction, incorrect lead placement, or insufficient output from the pacemaker. Instead, it is a reflection of the interaction between the pacing stimulus and the myocardial anatomy surrounding the pacing site, leading to the unique waveform changes observed. Understanding this concept is crucial for interpreting electrocardiograms and managing pacing strategies appropriately.