(a) Prominence of the spine seen posteriorly in the esophagus. (b) Schematic representation of esophageal landmarks and myotomy location. LHM laparoscopic heller myotomy
Technique
POEM has evolved significantly since inception with varying technical approaches based on the indication and per endoscopist preference. To understand the concept of POEM, it is critical to understand the anatomy of the layers of gastrointestinal wall – mucosa, submucosa, muscularis propria (inner circular and outer longitudinal muscle layers), and adventitia/serosa. It is important to note that the esophagus lacks a serosal layer unlike other parts of the GI tract. The beauty of POEM lies in the expansion of the microscopic submucosa to a space large enough to pass a >1 cm diameter upper endoscope with a distal attachment/cap, to perform myotomy under the protective net of the mucosal flap [3]. The technique for esophageal POEM is discussed here (Fig. 18.2a–e and Video 18.1), though the concept remains the same for other sites in the GI tract (the pylorus and rectum described elsewhere in this book).
Fig. 18.2
(a) Mucosotomy and endoscope entry into the submucosal space. M mucosa, SM submucosa, CM circular muscle, LM longitudinal muscle. (b) Submucosal tunnel extended beyond the GE junction and into the cardia. (c) Start of myotomy distal to the site of mucosal entry. (d) Myotomy extended to the cardia. (e) Mucosotomy closure [3]
Mucosal Incision
A distal attachment cap is fitted onto the tip of the endoscope, which helps to improve endoscopic visualization and accuracy of dissection during the procedure, in addition to facilitating entry into the submucosal space. A mucosal site for entry into the submucosal space is first chosen about 10–12 cm from the GEJ or based on the desired length of myotomy, which can vary depending on the indication (e.g., longer myotomy performed for type III achalasia). Any visible mucosal vessels or esophageal tortuosity is avoided when choosing the site for mucosal incision which may make submucosal entry challenging.
An injection needle is used to inject saline-methylene blue mixture (or saline-indigo carmine) at the site of the desired mucosal entry to create a submucosal lift (Fig. 18.3). Some endoscopists also add epinephrine (0.5–1 mg/100 ml of fluid) in the injection solution. After injection, an endoscopic knife is used with blended current (Endocut, ERBE USA, Marietta, GA) to make a 10–20 mm longitudinal mucosal incision. A transverse incision is used by some endoscopists as well, but less commonly since a longitudinal incision is easier to close at the end of the procedure. The mucosal incision is performed in the 1–2 o’clock position for an anterior myotomy or in the 4–5 o’clock position for a posterior myotomy (Fig. 18.4a, b).
Fig. 18.3
Submucosal injection
Fig. 18.4
(a) Incision for anterior myotomy . (b) Incision for posterior myotomy
We typically use Endocut Q: effect 3, duration 1 and interval 1 for the mucosotomy, but other variations such as Endocut Q: effect 2, duration 1 and interval 6, or effect 3, duration 2 and interval 4, or other settings can be used as well. The procedure can be performed with any endoscopic knife, based on endoscopist preference, usually a triangle tip knife (Olympus America, Center Valley, PA) or a hybrid knife (ERBE USA, Marietta, GA). Tang et al. showed shorter procedure time and less frequent device exchange with hybrid knife as compared to triangular tip knife, despite similar rates of procedure success and adverse events [4].
After mucosal incision, the exposed submucosa is dissected to create space for advancement of the endoscope. Special attention needs to be paid to identify the esophageal wall layers at this site and to not accidentally cut the underlying muscle layer since this would result in a full-thickness esophageal perforation at the site of mucosotomy. The endoscope is then carefully inserted into the submucosal space via the mucosotomy.
Submucosal Tunneling
Once the endoscope with the distal cap is in the submucosal space, the region is diligently inspected to confirm orientation of the esophageal wall layers. The loose submucosal tissue (stained blue after injection) has a characteristic blue “cotton candy” appearance (Fig. 18.5), with the mucosa on one side and the white muscle fibers on the other side. A submucosal tunnel is created with frequent injection of saline-methylene blue (or indigo carmine) solution and careful dissection of submucosal tissue using spray coagulation (effect 2, 50 W) or Endocut Q (effect 3, duration 1 and interval 1; or effect 3, duration 2 and interval 4) or forced coagulation (effect 2, 50 W) (ERBE USA, Marietta, GA). During tunneling, submucosal dissection should be performed with the knife closer to the muscle layer rather than toward the mucosal layer to avoid inadvertent mucosal perforation. The submucosal tunnel should extend at least 2–3 cm into the cardia beyond the GEJ. Extension of the tunnel into the cardia is confirmed by typical landmarks (distance from the incisors, submucosal space narrowing at the level of the lower esophageal sphincter and widening once the stomach is entered, and larger penetrating vessels and spindle veins seen in the stomach) as shown in Fig. 18.6a, b. This is also confirmed by retroflexed examination from the luminal side showing a submucosal blue bleb at the cardia bulging in the stomach (Fig. 18.7). Another strategy for confirming the location of the GEJ during tunneling is to pass a tandem ultrathin endoscope in the esophageal and gastric true lumen and visualizing transillumination from the endoscope in the submucosal tunnel [5]. Kumbhari et al. recently described fluoroscopic visualization of an endoscopically placed GEJ clip or fluoroscopy-guided placement of a 19G needle on the skin as marker for GEJ. The authors reported extension of the tunnel by a mean of 1.4 cm in about 20% cases while adding 2–4 min to total procedure time [6].
Fig. 18.5
Submucosal tunnel showing the submucosa stained blue
Fig. 18.6
Submucosal tunnel extending to the cardia showing (a) spindle veins and (b) penetrating vessels
Fig. 18.7
Retroflexed view of gastroesophageal junction showing bluish bleb extending into the cardia
Intervening submucosal vessels are coagulated with spray or forced coagulation with the dissection knife or with a Coagrasper (Olympus America, Center Valley, PA) with soft coagulation (effect 5, 50 or 80 W, ERBE USA, Marietta, GA).
Gentamicin lavage of the submucosal tunnel can be performed before beginning the myotomy but is not mandatory. Bayer et al. showed no major infectious complications post-procedure with or without gentamicin lavage, though leukocyte count and CRP levels were lower in the lavage group suggesting a possible reduction in systemic inflammatory response [7].
Myotomy
Tunneling is followed by endoscopic myotomy. Myotomy is started about 2 cm distal to mucosal entry site to avoid esophageal perforation or leak at the mucosotomy site. Just as for submucosal tunneling, the choice of electrosurgical settings during myotomy are variable as well, mainly dependent on endoscopist preference. Spray coagulation (effect 2, 50 W) or Endocut Q (effect 3, duration 1 and interval 1; or effect 3, duration 2 and interval 4; or effect 2, duration 1 and interval 6) or forced coagulation (effect 2, 50 W) (ERBE USA, Marietta, GA) can be used, but these are often modified based on the endoscopist, indication and location for myotomy, and the presence of scarring from prior interventions. The location, type, and direction of myotomy is evolving and being studied extensively.
Anterior Versus Posterior Myotomy
Anterior myotomy (2 o’ clock position, lesser curve side of the stomach) was the original location described in early Japanese literature as an extrapolation of the ventral approach during laparoscopic Heller myotomy (LHM) (Fig. 18.8a and Video 18.2) [1]. A posterior myotomy, on the other hand, is performed at the 4–5 o’clock position (Fig. 18.8b and Video 18.1).
Fig. 18.8
(a) Anterior myotomy. (b) Posterior myotomy
Partial-Thickness, Full-Thickness, and Progressive Myotomy
Partial-thickness myotomy involves selective incision of the circular muscles only, preserving the longitudinal muscle layer (Fig. 18.9a and Video 18.1), while a full-thickness myotomy is an incision of both the circular and longitudinal layers (Fig. 18.9b and Video 18.3). A progressive myotomy is a partial-thickness myotomy proximally in the esophagus which then blends into a full-thickness myotomy distally in the esophagus and at the level of the GEJ and cardia. A progressive myotomy toward the GEJ has been shown to reduce procedure time with similar efficacy and adverse events [8].
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