Acute changes produced by the different ablation energies
In our study, the LA wall thickness was found to increase similarly at
the level the PV ostia following ablation when using RF or laser balloon
energy, while no increase in wall thickness was observed when using the
cryoballoon. While acute development of tissue oedema is well known
after RF, 9,19,20, limited data are available
regarding acute tissue changes after laser energy
delivery13,21,22. Apart from the lack of direct
contact of the energy source with the tissue (the optical fiber
delivering arc of laser energy is in a balloon), laser energy as with RF
produces tissue damage through heating and is delivered in a
point-by-point fashion. Thus, it is not surprising that the two energy
modalities might share similar mechanisms of tissue injury, including
acute wall thickness increase from oedema. In the study by Mangrum et
al13, a significantly more pronounced wall thickening
was observed after RF ablation than after laser ablation, however a
lower RF power was used.
In another IVUS study11, tissue oedema was reported in
90% of the PVs after cryoablation (and similar number of freezes per
vein). Of note, in this study dissection-like changes were also
observed, together with oedema, in most of the PVs, while in our study
dissection-like changes were observed only in one vein after cryoballoon
ablation and, interestingly, this occurred in the context of acute wall
tissue thickening. It could be hypothesized that in these veins the
oedema was due to the mechanical injury associated with dissection,
rather than being a direct consequence of cryoenergy delivery. In the
sequential process of tissue injury produced by
cryoenergy23,24, tissue oedema is thought to occur
only at a late stage, once the tissue has thawed, following freezing,
and has become hyperaemic, and to gradually progress over subsequent
hours25. Concordantly, early PV imaging in our study
showed no acute wall thickening suggestive of development of oedema.
The different morphological changes produced by the different ablation
energies could suggest different mechanisms of lesion failure. Recent
data suggest that the adjustment of the ablation settings based on
baseline LA wall thickness can improve the procedure outcome and reduce
the risk of collateral injury12. A further adjustment
based on the acute wall thickening produced by energy delivery for
ablation could also be beneficial when using RF or laser energy and
could potentially highlight gaps between lesions.
Apart from acute wall thickening, we observed a reduction of the
thickness of the PV muscular sleeve after PVI catheter ablation.
Myocardial sleeves are known to extend from the left atrium into the PVs
walls and to be a source of focal activity triggering
AF26. The thickness reduction after ablation could
indicate damage, translating to elimination of the PV potentials and
acute electrical isolation of the vein and may also explain why it is
often impossible to get local capture during pacing to demonstrate
exit-block. Whether durable PV isolation correlates with a certain
degree of wall thickness reduction or complete disappearance of the
muscular sleeve after catheter ablation is unclear. We did not observe a
correlation between degree of wall thickness increase or muscular sleeve
thickness reduction after the first catheter ablation procedure and
evidence of PV reconnection at the second catheter ablation procedure,
however only a small number of PVs were checked with a second ablation
procedure in our study.