Guide to Endoscopic Selection for Per-Url Endoscopic Myotomy Procedures. Per-Url endoscopic myotomy is standard of care as a procedure for treatment of achalasia. There are multiple studies and educational resources discussing optimal approach, electro-surgical unit settings, and accessories for POM. However, there are currently no resources discussing the choice of endoscope to use. Our goal is to provide a comprehensive review of common endoscope choices, along with their advantages and disadvantages. There are multiple factors one needs to consider when choosing an endoscope to use for POM. The distal outer diameter of the scope may impact maneuverability within the tunnel. The accessory channel size is particularly important for suctioning during dissection and myotomy, especially when there are devices in the channel. The location of the channel also plays a pivotal role in tunneling, myotomy, and ergonomics of dissection. The working length of the scope may limit which accessory devices can be used. Tip angulation impacts maneuverability and is particularly important in cases with atypical anatomy. Finally, scope length, weight, and size are also important ergonomic considerations. Distal disposable attachments are important devices to use during POM, and they create distance between the distal tip of the scope and the lumen, as well as provide traction. There are multiple vendors which make various flat plastic caps that come in different sizes to accommodate most scopes. Some flat caps have a 4mm working distance with a small side hole to facilitate fluid exit from the cap. There are also tapered tip caps with a 7mm tip length. These may have the advantage of facilitating tunnel entry and maneuverability. Accessory devices such as injector needles, knives, hemostatic forceps, and hemostatic clips are typically compatible with all gastroscopes. However, there are certain devices that may not be compatible with slim colonoscopes due to their length. There are new intermediate-length slim colonoscopes that can eliminate this disadvantage. One of the most important characteristics of an endoscope is the size of the accessory channel. Scopes with a 3.2mm channel have superior suction capability compared to a 2.8mm channel. This is most apparent when there are devices in the channel. This becomes valuable in cases of bleeding or those with significant fibrosis requiring more injection into the submucosa during tunneling and subsequent pooling of fluid. The following video demonstrates the superior suction ability of a 3.2mm channel scope as seen on the left compared to a 2.8mm channel scope on the right. Both scopes have a 2.8mm compatible device, in this case a 4mm hemostatic forceps, and are attached to max suction. 50cc of saline is in both cups, and after 15 seconds one can see there is no saline in the cup on the left while hardly any liquid is removed from the cup on the right. Now we will highlight scopes from three different vendors and discuss their advantages and disadvantages for the use in POEM. The following table highlights key differences of various characteristics of the scopes. In general, diagnosis gastroscopes are commonly used for POEM given their relatively smaller distal and insertion tube outer diameters. Importantly, the accessory channel is 2.8mm for this vendor's gastroscopes, and the channel location is at 7 o'clock. There are thin colonoscopes with comparable distal outer diameters, however key differences are the larger 3.2mm working channel, the location at 5 o'clock, and the superior tip angulation capabilities. Of note, there is an intermediate length colonoscope, which is between the length of the standard colonoscope and gastroscope. The diagnostic gastroscopes made by vendor 1 come in two different outer diameter sizes, both with 2.8mm accessory channels. These scopes are compatible with all caps and standard accessory devices. The device comes out at 7 o'clock. For interior approaches, tunneling can potentially be easier and safer as the knife is aimed at the muscle layer. The shorter length of the scope is more ergonomically friendly and allows for more efficient device passage into the scope. We recommend using this scope in the setting of a narrow caliber esophagus. While this is likely the most commonly used scope for POEM, it may not be optimal for cases with anticipated bleeding, fibrosis, or a torturous esophagus, or in cases where pushability is important. Vendor 1 also makes two versions of a slim colonoscope, which has a similar distal outer diameter to the diagnostic gastroscopes, but a larger insertion tube. One key advantage of the scope is the superior tip angulations in the down, left, and right directions. The length of the scope may preclude passage of certain accessory devices, and the excess length outside the patient may be bothersome to some endoscopists during the procedure. The larger 3.2mm suction channel is particularly valuable, especially in situations with bleeding. The 5 o'clock location with a 6 o'clock waterjet is useful in posterior tunneling when encountering pooling of water posteriorly, and the location is also helpful in optimizing knife functioning and efficiency with scope torquing. The scope may be more optimal for cases requiring more pushability and maneuverability, as well as for situations with anticipated bleeding or fibrosis. One drawback is less optimal ergonomics given the scope length, weight, and dial size. The intermediate length of the scope eliminates some of these disadvantages. This is the preferred scope of one of the authors, who has used the scope for over 30 cases with a 100% success rate. Vendor 2 makes a few different gastroscopes which can be used during POEM. The differences with the diagnostic gastroscopes compared to Vendor 1 are the slightly different accessory channel location and the marginally longer working length, but instrument channel size is the same at 2.8mm. The larger diagnostic scope has a zoom feature, which may have some use during the procedure for certain endoscopists. The diagnostic gastroscope made by Vendor 2 is shown here. The distal end and shaft diameter, length, and channel size are similar to diagnostic gastroscopes from Vendor 1. However, one difference is the accessory channel location being closer to 6 o'clock. Like the slim colonoscope, the location improves optimizing knife functioning and efficiency with scope torquing. Like the diagnostic scopes made by Vendor 1, this scope is useful for cases with a narrow caliber esophagus. The optics are slightly different compared to Vendor 1 as well. Finally, the diagnostic gastroscopes made by Vendor 3 are highlighted in the table below. Key features to note are the 3.2mm instrument channel with a 9.9mm distal outer diameter, as well as the 5 o'clock channel location. The diagnostic gastroscope made by Vendor 3 is demonstrated here. While the distal end is similar in size to the 9.9mm diagnostic scopes from the other vendors, the key advantage is the 3.2mm instrument channel. To our knowledge, other than the slim colonoscopes made by Vendor 1, there are no other gastroscopes on the market in the United States with an instrument channel larger than 2.8mm. The device channel is closer to 5 o'clock. This scope has similar advantages to the slim colonoscope with the channel size and location, however has a smaller insertion tube size and working length. In conclusion, factors to consider when choosing which upper endoscope to use for poems include indication of the procedure, esophageal anatomy, accessory channel size, channel location, and tip flexibility. Endoscopes with a 3.2mm accessory channel have superior suction ability with devices in the scope, but aside from the slim colonoscope from Vendor 1, there are no diagnostic gastroscopes on the market with a 3.2mm working channel in the United States to our knowledge. Endoscopes with an accessory channel close to 6 o'clock may have more advantageous aspects for dissection and night functioning given natural alignment with the endoscope and a neutral location in plain dissection. Slim colonoscopes have some limitations with device compatibility and ergonomics, however intermediate length colonoscopes eliminate some of these disadvantages. This is one of the author's preferred scopes, while other authors favor gastroscopes for the optics and ease of use. If difficulty with one type of scope, endoscopists can consider the merits and demerits of other scopes to help troubleshoot a situation or to improve procedural efficiency.

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esophageal anatomy