Comparison with Previous Studies
LA WTs have been evaluated in post-mortem studies, revealing a
significant variation in the WTs among regions, patients, and
studies.1,2 Most of these studies reported average
thickness of LA myocardium between 1.0 and 5.0 mm with a range from 0.5
to 12 mm.1,2 The results in this study were almost
within this range but the average WT values were slightly thicker than
those in previous post-mortem studies. We measured the distance between
endocardial and epicardial boundary, which might be greater than the
actual muscular thickness in histological examinations. Fresh tissue
specimens also shrink after formalin fixation, causing a reduction of
WT. These factors likely contribute to the difference in the WT
measurement between previous histological studies and our ICE study.
Cardiac CT imaging has been used to evaluate LA WT in AF
patients,2,6-8 and therefore we compared the ICE-based
WTs measurements to cardiac CT-based WT measurements in the same
patients to validate the accuracy and reliability of our method; the
ICE-based WT measurements were almost similar to, or slightly thicker
than, the cardiac CT-based WT measurements in our study, suggesting the
similar accuracy of these measurements. The CT-derived WT averages
approximately 1.0-3.0 mm in previous reports. Of note, when viewed
alongside the results of the pathological studies in the similar
location, the CT measurements are reportedly lower than the histological
measurement.2
The left-PV anterior segment, the LLR, had the thickest wall among all
segments in this study. Cabrera et al. have reported that this region
has a folding structure with the thick muscle ranging from 2.2 mm to
12.3 mm.9 The morphology can be flat, round, or
pointed, as seen in this study (Figure 4).9 A previous
CT study has also shown that the LLR had the thickest walls in the area
surrounding the PV, which is consistent with our
results.6
ICE provides higher spatial resolution (0.2-0.3 mm) than cardiac CT (0.4
mm-) and MRI (1.4 mm-)2,10 and therefore seems to be a
good modality for the WT evaluation in the LA. ICE was used to assess
right atrial WTs in an experimental study.11 However,
it has not been used to assess WT in the LA of AF patients, likely
because of the invasive nature of this examination. The ICE has been
limited to use in procedures where its value has been clearly
established. The ICE catheter is usually placed in the RA for the
trans-septal puncture during AF ablation. In this study, the ICE
catheter was advanced into the LA, allowing clearer visualization of the
anatomy of the area surrounding the PV and reducing the angulation
errors of the view perpendicular to the LA/PV surface for the WT
measurement. Nevertheless, this assessment lacks a gold standard and
merits further evaluation.