Anterior Orientation vs Posterior Orientation in Per Oral Endoscopic Myotomy POEM for the Treatment of Achalasia

Achalasia is one of the most studied esophageal motility disorders. The etiology of Achalasia is autoimmune, neurodegenerative, or viral immune. Achalasia is a consequence of the degeneration of ganglion cells in the myenteric plexus of the esophageal body and the lower esophageal sphincter (LES). The end result of the inflammatory process is the loss of inhibitory neurotransmitters nitrous oxide and vasoactive intestinal peptide causing the imbalance between excitatory and inhibitory neurons. This results in failure of the lower esophageal sphincter (LES) to relax and is associated with aperistalsis of the esophageal body, leading to difficulty swallowing, food and fluid stasis; regurgitation of undigested food, fluid and saliva; and weight loss. Achalasia is an incurable disease and treatments are only focused on the relaxation of the lower esophageal sphincter in order to allow for passage of food fluid and saliva into the stomach. It has an estimated prevalence of 10 cases per 100,000 populations and an incidence of 1-3 cases per 100,000 populations per year in the Western world.

The armamentarium of Achalasia treatment includes pharmacologic management with the use of calcium channel blockers, nitrites, phosphodiesterase inhibitor (sildenafil), anticholinergics, and beta-adrenergic agonists; endoscopy using botulinum toxin injections just above the squamocolumnar junction or pneumatic balloon dilation of the lower esophageal sphincter; open Heller Myotomy, laparoscopic Heller Myotomy, and Per Oral Endoscopic myotomy (POEM). Per oral endoscopic myotomy (POEM) is the most recent innovative treatment in the armamentarium of Achalasia treatment. Per oral endoscopic myotomy (POEM) is a natural orifice transluminal endoscopic surgery (NOTES) approach to a Heller myotomy for the treatment of Achalasia. In 2008, POEM was first performed successfully in a human subject by Haruhiro Inoue in Japan. The POEM was performed on a 36 year old patient without any documented post-operative complications. In 2009, Stavros Stavropoulos at Winthrop University Hospital (WUH) performed the first per oral endoscopic myotomy (POEM) procedure outside of Japan. The POEM was performed on a 42 year old male without documented post-operative complications. The subject had a marked improvement in objective manometric and barium esophagram findings; and improvement in subjective dysphagia score. Consequently there has been a rapidly increasing volume of POEM procedures performed in Japan, China, and throughout the United States. Stavropoulos at Winthrop University Hospital has the highest single-operator volume in the United States. The performance of POEM is still in evolution with various centers around the world performing variations on technique.

The International Per Oral Endoscopic Myotomy Survey (IPOEMS) was conducted by Stavropoulos and Savides during the July 2012 annual meeting of Natural Orifice Surgery Consortium for Assessment and Research (NOSCAR). This survey was conducted to address the scarceness of POEM literature at the time. IPOEM provided a "snapshot" of the status of POEM worldwide. The survey included 5 Asian, 7 North American, and 4 European expert centers with a combined total of 841 POEM procedures performed by July 2012. At the time most centers (14) performed right anterior myotomy (2 o'clock orientation) with only a few of centers performing posterolateral myotomy (5 o'clock orientation) determined using the usual endoscopic convention of 12 o'clock representing the most anterior aspect of the esophagus on endoluminal view.

The esophagus in humans is a complex structure with multiple muscles, nerves, vascular, and lymphatic components. Branches of the vagus nerve and visceral branches of the sympathetic trunk provide nerve fibers to the esophageal plexus. The vagus nerve delivers two fiber types to the esophageal plexus: preganglionic parasympathetic fibers and afferent fibers. These vagal fibers in the esophageal plexus reform to make the anterior vagal trunk (left vagus) and the posterior vagal trunk (right vagus). The anterior and posterior terms for the vagal trunks are used in relation to the esophagus. The visceral branches of the sympathetic trunk delivers two fiber types to the esophageal plexus: sympathetic postganglionic fibers and the afferent fibers. The afferent fibers originating from the sympathetic trunk are primarily involved with pain. The critical anatomical component of the esophagus in the treatment of Achalasia is the lower esophageal sphincter. Per common convention, the most anterior point of the LES point is assigned as the 12 o'clock position. The strong oblique sling fiber component is centered at 7o'clock on the posterolateral wall and wraps over the anterior and posterior walls at 11 o'clock and 5 o'clock, respectively. The weaker circular clasp fiber component location is centered at 2 o'clock to 3 o'clock. The question of investigating the optimal orientation to perform the myotomy is unique to POEM. Open Heller myotomy and laparoscopic Heller myotomy are limited to the anterior aspect of the esophagus. Myotomy orientation is constrained by the anatomical locations of the left bronchus, left atrium and spine. Anterior orientation is forced between the 1 o'clock - 2 o'clock position secondary to the locations of the left bronchus and left atrium between 10 o'clock -11 o'clock and 12 o'clock - 1 o'clock, respectively. Posterior orientation is forced between the 4 o'clock - 5 o'clock positions secondary to the location of the spine located between 8 o'clock-9 o'clock positions .The sling fibers maintain the angle of His and are a significant antireflux barrier. Stavropoulos et al, reported on a single operator series of 284 POEM subjects at Digestive Disease Week in May 2016. A statistical difference was found in the number of subjects requiring narcotics post POEM procedure Subjects who had an anterior myotomy were less likely to require narcotics post POEM procedure than those subjects who had a posterior myotomy, 35% versus 53% respectively (p=0.007).

To date, there have been no prospective randomized controlled studies conducted comparing anterior versus posterior myotomy technique in POEM analyzing perioperative pain, procedure duration, incidence of mucosotomy, capnoperitoneum, and the postoperative sequelae of gastrointestinal reflux disease (GERD).