Pseudofusion Beats

Report:

Atrial pacemaker rhythm 64/min 2

SVEB 3

Pseudofusion beats 4

Nonspecific ST/T changes 1

Comment:

The QRS complexes are normal except for the ventricular pacing spikes at their onset. They are not fusion beats – the SVEB is preceded by an atrial spike only and looks just the same. They are called pseudofusion complexes because what takes place is mere superimposition of signals rather than any physiological reality. In some minds, however, this concept is less clear: Wagner’s new edition of Marriott’s Practical Electrocardiography defines fusion as “merging of waveforms (i.e., P and T waves) together”10. The only reason that Marriott is not turning in his grave is that he’s still living!

There is no pacemaker malfunction: the ventricular electrode just misses out on sensing the native QRS and being inhibited. Pseudofusion beats are quite common in paced patients and are not routinely reported; neither are the true fusion beats. In this case, because they occurred all the time, the AV interval was reprogrammed to a slightly longer one and the ventricular pacing spikes disappeared (below). Saves the battery.