Endoscopic submucosal dissection (ESD) is an advanced endoscopic technique used to remove superficial gastrointestinal (GI) tract neoplasms. This technique has advantages enabling en bloc resection regardless of the tumor size [1]. The resection margins of tissue removed en bloc can be accurately evaluated in all directions by pathologists. Thus, local recurrence can be reduced by determining whether the lesions are completely resected [2]. Despite these advantages, ESD is not popular worldwide because of technical difficulties and high-risk complications. Thus, various types of endoscopic knives have been developed to overcome these technical difficulties; these include insulated tip knife-type (IT knife, IT knife 2, and IT knife nano), needle knife-type (hook knife, dual knife, flex knife, B-knife, and hybrid knife), and grasping scissor knifetype (SB knife, SB knife Jr, and Clutch cutter knife) [1,3]. These endoscopic knives have helped remove lesions more safely and effectively but can cause intraprocedural or postprocedural bleeding because of the electrosurgical current.

Bleeding is one of the most common complications associated with ESD, as intraprocedural bleeding interferes with precise endoscopic resection under a clear view of the operating field, which can lead to longer procedure times or an increase in the frequency of complications, such as perforation [4]. The incidence rates of immediate and delayed bleeding associated with gastric ESD are approximately 22% and 4.5%–5.5%, respectively [5-7]. A recent meta-analysis showed that the incidence rates of immediate and delayed bleeding associated with colorectal ESD are 0.82% and 1.7%, respectively [8].

Lasers generate heat and cause edema in the vessel wall, resulting in hemostasis [9]. Therefore, attempts have been made to reduce the risk of bleeding associated with these laser properties by using several types of lasers, including carbon dioxide (CO₂) laser [10,11], Nd: YAG laser [12], thulium laser [13], and diode laser [14], for endoscopic procedures.

The diode laser system has been used as a surgical instrument for incising and dissecting tissue and for achieving hemostasis. However, no study has yet performed ESD using the 1,940-nm diode laser system. A new medical fiber-guided diode laser system (FDLS) designed for endoscopic procedures emitting a high-frequency 1,940-nm wavelength is expected to offer high-precision cutting with simultaneous hemostasis. Thus, this study aimed to evaluate the feasibility of the application of the FDLS for performing ESD in the GI tract of an animal model.

This study was designed as a prospective animal pilot study. Herein, the feasibility of endoscopic application of the FDLS in ESD was evaluated in ex vivo and in vivo porcine models. An ex vivo porcine model was used first to confirm the feasibility of FDLS application for ESD, followed by an in vivo porcine model to assess its clinical applicability.

ESD is one of the most technically difficult endoscopic procedures. According to the recently updated guidelines of the Japan Gastroenterological Endoscopy Society, understanding anatomical features and familiarity with the basic techniques of polypectomy, endoscopic mucosal resection, endoscopic hemostasis, and clip suture are the minimum requirements before starting ESD [15]. Novices must practice using ex vivo or in vivo animal models or in the clinic under a supervisor to perform ESD more safely and efficiently. Several animal and clinical trials reported that at least 30 cases of gastric ESD should be performed to achieve an acceptable technical level [16,17]. However, one study reported that a high technical level cannot be reached until more than 240 cases of colorectal ESD have been performed [18].

Several factors increase the difficulty of ESD, including intraprocedural bleeding, paradoxical scope control, non-lifting lesions, perpendicular submucosal approach, ineffective gravity countertraction, and submucosal fibrosis [19]. The incidence of intraprocedural bleeding during ESD is >20% [20], and proper management of bleeding plays a critical role in successful ESD because it interferes with precise cutting under clear vision.

Several studies have evaluated the clinical effectiveness and applicability of various types of laser devices capable of precise tissue cutting without intraprocedural bleeding during ESD. Cho et al. [13] reported preliminary results of gastric ESD using thulium laser. Ten patients underwent ESD using thulium laser without an endoscopic knife, and the curative resection rate was 90% (9/10). No active intraprocedural bleeding, delayed bleeding, or perforation was detected. Preliminary results of gastric ESD were also reported with the use of CO₂ laser in ex vivo and in vivo porcine models. En bloc resection was achieved in all eight gastric ESD (five ex vivo and three in vivo) cases, and there was no perforation, MP layer injury, or uncontrollable hemorrhage observed during the procedures [11].

The diode laser system has been used for a variety of surgeries, such as prostate disease surgery [21], endovenous ablation treatment [22], tonsillectomy [23], and laser-assisted laparoscopic partial nephrectomy [24], and has proven to be effective for tissue excision and hemostasis. Tang et al. [14] demonstrated the feasibility of ESD using diode laser in an animal model. Eight cases of esophageal ESD were performed using the synchronous 980/1,470-nm dual-diode laser system, achieving a 100% en bloc resection rate without perforation. The procedure speed of ESD was significantly faster using the dual-diode laser system than using a conventional endoscopic knife (0.27 cm²/min vs. 0.21 cm²/min, p=0.001). In addition, fewer intraprocedural bleeding points were detected, and the use of hemostatic forceps was significantly less frequent in the diode laser ESD group than in the conventional ESD group. However, studies on diode laser-assisted ESD are very rare. The 1,940-nm diode laser system, as demonstrated in tonsillectomy, is capable of precise excision of the mucosa and submucosa without intraoperative bleeding; however, no studies related to endoscopic procedures have been published [23]. To apply these advantages of diode laser to ESD, we conducted gastric or colorectal ESD using a specially designed fiber optic laser catheter that enables tissue cutting through the endoscope working channel, similar to an endoscopic knife.

In our ex vivo study, en bloc and complete resections were achieved in all 10 cases of colonic ESD using the FDLS. Perforation occurred in the first case of colonic ESD because it was initially difficult to maintain the proper cutting direction using the FDLS. Afterwards, only minor MP layer injuries occurred, without any perforations in the remaining cases. As the operator adapted relatively quickly, the number of MP layer injuries (0.2±0.4 vs. 1.4±1.9) and procedure time (25.2±8.1 min vs. 40.8±12.2 min) were lower and shorter, respectively, and the procedure speed (1.04±0.21 cm²/min vs. 0.70±0.31 cm²/min) was faster in the last five cases than in the first five cases.

In our in vivo study, the en bloc resection and perforation rates were 100% and 12.5%, respectively, although most endoscopists had no experience with ESD using the FDLS. No intraprocedural bleeding occurred; however, MP layer injuries were more frequent during rectal ESD (25% grade 1, 25% grade 2, and 25% grade 4 injuries) than during gastric ESD (50% grade 1 injury). These results probably occurred because the colon wall is thinner than the stomach wall, and the colon lumen is narrower than the stomach lumen, making endoscopic manipulation difficult.

Based on the results of our study, FDLS-guided ESD has some advantages, such as a low risk of bleeding and safe cutting in the area of submucosal injection. Intraprocedural bleeding did not occur in this study. If it had occurred, it is expected that hemostasis would have been achieved with the FDLS using the non-contact technique without changing to other hemostasis devices. The FDLS enabled cutting the mucosa or submucosa very safely after the submucosal injection because the output wavelength of a 1,940-nm laser coincides with the absorption peak of water. In addition, the high absorption coefficient of a 1,940-nm laser allows a shallow penetration depth, enabling precise ablation with less thermal damage [23,25]. When the resected specimens were evaluated histologically, the cutting surface was observed accurately enough to judge whether the lesion was completely excised (Fig. 5).

However, there were some disadvantages when using this device. The FDLS-guided ESD technique differs from the conventional ESD technique. Conventional needle-type ESD knives enable tissue resection of any tissue in contact with the metal tip; however, the apex of the tip can be used to resect the tissue when using the fiber-optic laser catheter. This limitation made it technically difficult to secure an appropriate resection plane when the lesion was in a perpendicular position. Thus, it was important to maintain a safe resection plane parallel to the MP layer during submucosal dissection.

Some limitations of this study should be discussed. The sample size was small, and we did not reflect the condition of the patients’ breathing or heartbeat. We selected the optimal location for the ESD procedure and did not compare it with the use of conventional endoscopic knives. Despite these limitations, this is the first study to investigate the usefulness of the 1,940-nm FDLS for gastric and colorectal ESD. Large animal trials or human clinical trials are needed to confirm the advantages of this device over conventional endoscopic knives.

In conclusion, the 1,940-nm FDLS was capable of yielding a high en bloc resection rate without intraprocedural bleeding during gastric and colorectal ESD in an animal model.