Discussion

Our study first quantitively illustrated the TEE feature of acute LAR lesion CB ablation combined procedure, and explored its influence on clinical outcomes. Our primary findings are: 1. Prominent acute LAR lesion after CB ablation combined procedure could be frequently observed, with a larger increment in width than thickness, 2. Higher LSPV nadir temperature poses a higher incidence of 2-fold wider LAR lesion, 3. Acute LAR lesion has no influence on overall combined procedure outcome, but it affects measurement of pacifier device.
LAR—also known as coumadin ridge—had long been mistaken as a thrombus attached to LAA revealed by transthoracic echocardiography (TTE). Until 2008, a 3-dimensional TTE study demonstrated that the high-echo attachment was a normal variant (16). LAR is an invagination between the left PVs and LAA. A recent cadaveric study by Piątek-Koziej et. al. (1) presented that the appearance of LAR varies, and the width of 7.9±3.2 mm and the whole wall thickness of 4.3±1.8 mm at the level of LSPV ostium. While in our study, we measured a smaller preprocedural width of 5.2±1.6 mm/5.7±2.2 mm and a larger thickness of 11.0±3.8 mm/13.1±4.1 mm at 45°/90° planes. We believe that the minor inconsistence is reasonable due to the difference between paraformaldehyde processed specimens and TEE measured intravital LAR.
Acute edematous change of LAR following ablation has been reported by several researches on combined procedure (8,9). Similarly, it was observed in almost every patient in our study, with a greater increment in width (Δwidth=3.6±2.3 mm) than thickness (Δthickness=2.6±3.5 mm). From a basic aspect, we believe that “edema” is rather imprecise albeit it subsides during follow-up. Study confirmed that lesion caused by thermal ablation is primarily composed of not only interstitial edema, but coagulative necrosis and hemorrhage (17). Besides, compared with radiofrequency (RF), cryo-energy ablates local tissue through a different mechanism that direct damage cellular structure and cause vascular failure (18). Yamashita et al. (19) compared ventricular lesion after cryo and RF ablation by MRI, and they found although the edematous change were compareble, the time-course of the cryo lesion differed from that of RF. We believe the feature of acute LAR lesion caused by cryo-ablation is different from RF, and it requires further imaging or histological confirmation.
Interestingly, we only found a higher balloon temperature correlates with a higher incidence of 2-fold wider LAR lesion at 45°. Previously, a study done by Miyazaki et al. (20) has demonstrated the acute PV edema in 10 patients via intracardiac echocardiography, while they found a lower right superior PV (RSPV) nadir balloon temperature in the group with thicker edema (−49.3 ± 0.6 vs −58.8 ± 2.0℃). However, their sample size is relatively small and they only find such relationship at RSPV. A study has shown that a high balloon temperature indicates incomplete sealing of PV (21) that could result from mismatch of small CB and large PV antrum as commonly seen in persistent AF. In this situation, further advancement of CB into PVs is required to achieve sealing, which moves CB distally to LAR. Subsequently, less cryo-energy will be delivered to LAR, and reversible vascular impairment predominates and lead to bulked lesion. We believe a more suitably matched CB with LSPV antrum could minimize the lesion size, while more well-designed studies focusing on LAR lesion size and freezing parameters are warranted to support the idea.
Although we found the LAR lesion had no influence on either early or late recurrence and clinical outcomes, the impact on LAAC with different types of LAAC device is noteworthy. In our study, there was little change of the inner ostium diameter in the presence of LAR lesion. Therefore, it had hardly no influence on measurement and closure for plug device (Watchman) that land to the inner ostium of LAA. Follow-up TEE further confirmed that only minimal residual flow occurred in 4 patients implanted with Watchman, and all residual flow presented on the inferior border rather than LAR side.
However, the outer ostium diameter reduced significantly after the procedure (Δouter ostium diameter=-3.4±4.0 mm), and it expanded to its original size in the 3rd month follow-up. In this situation, the selection of pacifier device (that requires gauge of the outer ostium) could be masked by the acute bulked lesion. During follow-up, 2 out of 9 patients implanted with LAmbre device (size 24×30 mm) developed residual flow on the LAR side. TEE reveals that both patients had distinct bulked lesion and reduced outer ostium diameter (30 mm) when performing combined procedure. Although the sample size of LAmbre combined procedure is too small to detect a statistical difference, masked outer LAA ostium interferes the selection of pacifier device size. We recommend that the size of the outer disc should refer to the measurement before ablation or a larger size outer disc should be chosen if measured after ablation. More randomized controlled studies are warranted to provide stronger evidences on choosing pacifier LAAC device during combined procedure.
Our study should be interpreted with caution. First, we uniformly applied CB ablation to achieve PVI, the conclusion cannot be extrapolated to RF and other ablation techniques. Sencondly, only 96 out of 117 TEE image series were available for measurement, the LAR lesion remained unknown in the others, and the incidence of device related event could be underestimated. Thirdly, all the TEE images were centered at LAA rather than LAR. Although the LAAC complications were precisely evaluated, the measurement of LAR and LAR lesion could be biased. Fourthly, our postprocedural images were obtained after LAAC procedure rather than instantly after CB ablation and before LAAC. Thus, the LAR could be stretched and deformed due to the expansion of LAAC device, which poses a potential bias. In addition, although we used both Watchman and LAmbre devices to explore the relationship between LAR lesion and different types of device, only 9 patients were implanted with LAmbre, which is insufficient to detect a statistical difference. Larger scaled randomized controlled studies are required to further address the issue.