Electrophysiological diagnosis: key role of entrainment
pacing
Although a minority pattern, a ”QS” unipolar electrogram was recorded at
the breakthrough site of our series of pseudo-focal ATs, confirming
previous observation by Pathik et al. Such pattern is theoretically not
compatible with an ”epi-endo” breakthrough. However, in clinical
practice, unipolar electrograms have been used on the basis of a
two-dimensional analysis that considered atrial surface only, without
including atrial depth as a third dimension. Thus, the extent to which
theory can be applied to the standard recording of a 3-mm thick atrium
is unknown, especially if the layers have been previously ablated and
are tangentially blending into one another.5 This
illustrates a limitation of high-density mapping systems if the operator
exclusively relies on activation maps based on automatic electrogram
recording and annotation.
From this respect, the present study shows that the strongest evidence
for a macroreentry is provided by conventional maneuvers as simple as
entrainment pacing. Although mostly close to a collision site, our data
show that ”epi-endo” breakthrough sites can sometimes be more than 50 mm
remote from a collision site. Hence, entrainment pacing maneuvers should
be systematically performed in ATs with centrifugal propagation in order
to rule out a macroreentry. Barbhaiya et al. have demonstrated that
entrainment pacing with a pacing cycle length of < 20 ms
shorter than TCL resulted in an extremely low risk of AT alteration or
termination.11 Due to slow conduction at the
epicardial bypass, the mean TCL was over 300 ms in our case series. This
long TCL might have even reduced the risk.