Measurements of LAPW thickness
Analyzing the 298 hearts obtained from the autopsied cases, Platonov et
al. directly measured LAPW thickness and found that LAPW thickness was
2.1-2.9 mm, being thinner at the site between the superior PVs than at
the site between the inferior PVs.13 The results on
the thickness per se were concordant with our findings by ICE, but in
our real-time assessment, the thickness was thinner at the LIPV level
than at the LSPV level. It is important to note that our measurement was
done during the AF ablation procedure in a real-time fashion. Variation
in the thickness among the LA regions was observed in CT
studies.14,15 With the use of the CT scan images,
Beinart et al. reported that there was a large range of LA wall
thickness (average thickness 1.89 ± 0.48 mm, range 0.5-3.5 mm), and in
particular, the LA roof was significantly thicker than the posterior
wall and floor.15 Though CT is useful in assessing the
LA wall at various sites, its resolution is not necessarily high and
real-time assessment of LAPW thickness adjacent to the esophagus cannot
be obtained at the time of AF ablation.
In the present study, we used ICE to measure LAPW thickness during
cardiac catheterization procedure just prior to AF ablation. ICE
provides the higher spatial resolution (with a maximum spatial
resolution of 0.2-0.3 mm) compared with cardiac CT even with 256
multi-slice CT (voxel in plane of 0.8-1.0 mm and slice thickness of 0.4
mm) and cardiac MRI (1.4 mm).16,17 ICE has been
demonstrated to accurately assess in the right atrial wall thickness in
an experimental model.18CartoSoundstarⓇ produces imaging variable frequencies
from 4.5 to 11.5 MHz, thus providing near-field clarity within 5 to 7 cm
of the transducer. CartoSoundstarⓇ can provide to
visualize the detailed cardiac structure and other structures of
interest including the esophagus when introduced directly into the LA
cavity. Thus ICE with CartoSoundstarⓇ enables precise
measurement of the distance between the endocardium of the LAPW and the
outer layer of the esophagus and would provide an important information
on the LA wall thickness when delivering the RF energy to the LAPW,
especially to the thinnest site.
ICE offers visualization of the LA in a real-time fashion during the
course of the procedure and can identify all structures for ablation
accomplishment. A real-time imaging by ICE has a significant advantage
compared with CT, since there is a time interval for CT scan between the
image taking and ablative procedure, during which changes in the LA
volume may occur. The incorporation of LAPW thickness measurement and
information on the relative location of the esophagus to the LA with ICE
may be useful in accomplishing the safer ablation procedure in the LA
posterior wall, including the selection of less risk site and
application of not-excessive contact force and RF power.