POEM represents an incisionless method to duplicate the traditional surgical myotomy by the ingenious concept of creating a submucosal tunnel that allows one temporary access to the mediastinum and esophageal muscle, including the LES, before the tunnel entrance is securely closed. Thus, the elements of POEM technique are as follows: (1) mucosal incision, (2) submucosal tunnel creation, (3) esophageal myotomy, (4) LES myotomy, and (5) entry point closure (Figs. 6.2 and 6.3). The entry point site varies depending on the indication, but is typically 10–15 cm proximal to the GEJ [6].

As demonstrated in the IPOEMS study, there is no consensus regarding orientation [8]. Some centers perform POEM anteriorly at the 2 o’clock position (in the usual convention of the posterior wall centered at 6 o’clock) as initially advocated by Inoue, although he appears to have recently changed his preferred approach to a posterior approach [11]. Other centers, such as Winthrop in New York and Zongshan in Shanghai, have favored a posterior orientation at the 5 o’clock position. Various theoretical advantages have been proposed for one approach over the other. Since the posterior approach may cut some of the more powerful sling fibers of the LES compared to anterior myotomy, which is limited to the shorter and weaker clasp fibers, we have argued as early as 2013 that “one could speculate that centers employing a posterolateral approach (5 o’clock orientation), thus cutting a portion of the posterior sling fibers, may achieve higher efficacy in dysphagia relief but possibly at the cost of increased reflux” [8, 16].

It should be noted that in certain situations an anterior or posterior orientation is forced by a prior HM (in which case a posterior approach is selected to avoid postsurgical changes/scarring), or lesions such as ulcerations due to food stasis, pulsion diverticula, and severe angulation of the lumen. No prospective, randomized, comparative data have been published to date. Our group is currently near completion of enrollment of patients in a single-center, randomized study comparing anterior and posterior orientation.

We recently presented preliminary data from a retrospective comparison of anterior and posterior POEMs in our large, single-operator series using data from a prospectively maintained database [17]. In this study, we analyzed all POEMs performed at our center from October 2009 to October/2015, 248 consecutive POEMs (120 anterior, 128 posterior), all successfully completed, with no aborted POEMs or surgical conversions. No learning curve bias was expected as we performed a similar percentage of anterior POEMs in the first 3 years of our series (48/91, 53%), as in the last 2 years (72/157 46%). There were no differences in the Eckardt score, including failures (post-POEM Eckardt score >3, 5/110 anterior vs. 4/117 posterior, p = NS), accidental mucosal injuries (including non-transmural minor blanching, 29% vs. 23%), or prolonged stay of >5 days (one patient in each group). There was no difference in significant adverse events (AEs), but it should be noted that there was a paucity of such events in our series, with no leaks, no tunnel bleeds, and no surgical/IR interventions. Posterior POEM was significantly faster overall (97 min anterior, 79 min posterior, p = 0.0007) including a faster closure (suturing 177, clips 71) (9.6 min anterior, 7.9 min posterior, p = 0.02). More patients had pain requiring narcotics in posterior POEM (17% anterior vs. 27% posterior, p = 0.007). There was a trend for less acid exposure in anterior POEM: +BRAVO studies (21/58 (36%) anterior vs. 29/58 (50%) posterior, p = 0.13) and reflux esophagitis (22/57 (38%) anterior vs. 33/60 (55%) posterior, p = 0.076).

Once orientation and location is selected, the submucosal space is expanded by saline injection to allow the endoscope to enter. An incision is made in the esophageal mucosa over this saline cushion, and a tunnel is begun with an electrosurgical knife inserted through the instrument channel. When the tunnel is deep and wide enough to permit introduction of the cap-fitted endoscope, it is then inserted and tunneling is continued with electrocautery distally toward the stomach. Usually, epinephrine is not utilized to avoid ischemia of the mucosal flap that may lead to necrosis. The endoscope is advanced as submucosal dissection is continued, and a tunnel is created within the submucosa from the middle esophagus to the gastric cardia. Meticulous care is taken not to tear the mucosal “roof” (or “floor,” depending on the approach) of the submucosal tunnel.

The myotomy is generally performed after the tunnel creation, but recently, a technique has been described where the submucosa and muscularis are dissected simultaneously, possibly resulting in shorter procedure times [18, 19]. Some operators prefer the triangle-tip (TT) knife (Olympus, Center Valley, PA, Fig. 6.4a), while others, such as our group at Winthrop and the Shanghai group, prefer the multifunctional hybrid knife (HK) that can perform submucosal injection and dissection (ERBE, Tubingen, Germany, Fig. 6.4b). In their randomized controlled trial of 100 patients comparing POEM performed with the TT knife versus the HK [20], the Shanghai group reported that the HK produced significant decreases in POEM procedure time (22.9 vs. 35.9 min) (p < 0.0001) and fewer minor bleeding episodes, with no differences in complications or treatment success. This improvement in procedure times was mostly attributed to fewer exchanges of accessories. Similar results were also reported in a case–control study comparing the TT knife and the HK [21].

The incision site may be closed effectively with either clips or endoscopic sutures. Our group published data of a retrospective comparison of clips and suturing indicating similar closure times and cost for suturing versus clips [22]. Another US surgical group using much smaller numbers in a retrospective analysis of only 5 cases per group reported very long closure times with suturing (mean of 33 min), which, in their analysis, resulted in higher overall cost for suturing despite similar equipment cost to clips [23].

Infection is prevented by meticulous removal of retained food from the esophagus prior to beginning the tunnel, secure closure of the esophagotomy, and prophylactic systemic antibiotics. Many centers also perform antibiotic lavage of the tunnel prior to closure as recommended by Inoue [6].

There is significant variation in technique between POEM operators in terms of entry point (site and orientation), myotomy length, submucosal injection, mode of dissection, myotomy depth, and closure methods, all of which may vary depending upon procedure indication, operator preference, local expertise, etc. In addition, ancillary procedures to confirm adequate myotomy length may vary [24]. For instance, a myotomy of 5 cm length should suffice for most patients with Chicago Classification Achalasia types I and II, but an extended myotomy ranging to at least 15 cm may be necessary in type III achalasia patients, diffuse esophageal spasm, and jackhammer esophagus [25, 26].

A greater curvature (extended gastric) myotomy may be considered in subjects with prior HM or POEM [27]. Extension of the myotomy to the cardia is important, even without prior Heller procedure, to ensure complete LES ablation. A variety of indicators that suggest that the GEJ or cardia has been reached include the following: (1) endoscopic measurements (using the markers on the endoscope to measure depth of insertion from the incisors); (2) narrowing of the submucosal space at the GEJ with resistance to endoscope insertion caused by the LES, followed by prompt expansion of the submucosal space in the cardia with increased overall vascularity of the submucosa; (3) slender palisade vessels along the mucosal flap, indicating the distal-most aspect of the esophagus; (4) spindle-like veins on the surface of the muscularis propria near the GEJ; (5) large-caliber, arborizing, perforating vessels in the cardia (usually branches of the left gastric artery); (6) aberrant inner longitudinal muscle bundles at the GEJ originating from circular muscle fibers and inserting into circular muscle fibers after a short course of 2–3 cm; and (7) visualization of a blue hue on intraluminal inspection of the mucosa of the cardia (due to the blue color of the injectate) [12].

A transillumination auxiliary technique, initially described by Baldaque-Silva and colleagues, allows confirmation that the tunnel was extended into the cardia by inserting an ultrathin endoscope transnasally in parallel with the orally inserted gastroscope used to perform the POEM procedure. The ultrathin scope is advanced to the level of the stomach and placed in the retroflexed position with visualization of the cardia, while the gastroscope is kept within the tunnel with its tip at the tunnel terminus. The light intensity of the thin endoscope is diminished, and the light from the gastroscope within the submucosal tunnel is identified, thereby confirming its position in the cardia [28]. Inoue’s group compared this technique to conventional identification of the cardia by the indicators listed above in a prospective randomized controlled trial with 100 consecutive achalasia patients undergoing POEM. POEM was completed with high rates of technical and clinical success in both groups, with low adverse events, but the double-scope transillumination group had myotomy extension in 34% of cases, which led to an increase in the length of the cardiomyotomy from 2.6 to 3.2 cm (p = 0.01) [29]. Despite the extension of the myotomy in a third of the patients in the transillumination group, suggesting that the final length of the cardiomyotomy of the control group may have not been of adequate length in a third of patients, there were no differences in clinical success rates, and no differences in postprocedure gastroesophageal reflux disease (GERD), thus raising doubts about the clinical utility of the double-scope method. Some drawbacks of this technique are that it may require two operators, is cumbersome, requires a second endoscopy tower and endoscope, and adds significant time to the procedure (17 min in this study). However, this technique may be beneficial for difficult cases such as those on patients with sigmoid end-stage achalasia or for operators early on the POEM learning curve.

Another technique for reliably identifying an adequate myotomy extension into the cardia involves the use of fluoroscopy. Kumbhari reported using either a hemoclip attached to the GEJ or the fluoroscopically guided placement of a 19-gauge needle on the skin at the level of the GEJ to help accurately assess the length of the myotomy in 24 consecutive patients undergoing the POEM procedure. Based on the fluoroscopic information, the submucosal tunnel was extended in 21% of patients, with minor increases in procedure time (4 min for the hemoclip group and 2 min for the 19-gauge needle group) [30]. Another group has also reported on the use of fluoroscopy to ensure proper orientation and extension of the tunnel into the cardia particularly in challenging cases with sigmoid esophagus [31].

Adequacy of LES ablation may also be assessed by real-time measurement of the GEJ distensibility with a balloon-based imaging probe (EndoFLIP, Crospon Ltd, Galway, Ireland) that uses impedance planimetry and can been used during the procedure to assess the adequacy of the myotomy via measurements that include GEJ cross-sectional area (CSA), minimal diameter, compliance, and distensibility [32–36].

Patients are kept nil per os until a water-soluble contrast study is performed when the patient is awake to exclude a leak, though it has little bearing on ultimate efficacy [37]. Most patients can be discharged soon after the tolerance of food.