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.