Simple mathematical equation to predict distance to gastroesophageal junction through the submucosal tunnel during peroral endoscopic myotomy

Background and aim Accurate estimation of the distance to the gastroesophageal junction (GEJ) through a tunnel during per oral endoscopic myotomy (POEM) is technically challenging. The methods currently employed are often insufficient, and resultant errors may lead to incomplete myotomy and/or prolonged procedure times. Our hypothesis states that the additional distance while traversing the tunnel is directly proportional to the widest esophageal diameter; and is calculated by the formula X = Y + CZ (X = distance to the GEJ through the tunnel, Y = distance to the GEJ through the lumen, Z = widest esophageal diameter, C = arithmetic constant). This study evaluates the validity and accuracy of this hypothesis. Patients and methods This was a prospective single-center study with 80 patients, 12 in the pilot group and 68 in the study group. In the pilot group, Y was recorded during esophagogastroduodenoscopy (EGD) before POEM, Z on barium swallow/contrast enhanced computed tomography (CECT), and X was measured during POEM. Using the formula, mean C (SD) was calculated. In the study group, ‘C’ was substituted in the equation to predict the GEJ distance through the tunnel (Xp) before POEM. The operator was blinded to Xp and recorded the true Xt during POEM. The correlation between Xp and Xt was calculated. Results In the pilot group, the mean distances (cm, SD) for X, Y, and Z were 42.58 (3.33), 39.83 (3.08), and 4.39 (1.16), respectively. The calculated mean C was 0.63 (0.11). In the study group, the mean distances (cm, SD) for Y, Z, Xp, and Xt were 40.45 (2.58), 4.99 (1.43), 43.57 (2.68), and 43.54 (2.78), respectively. The Xp and Xt values demonstrated a high correlation (r = 0.97, P = 0.000). Conclusions Formula X = Y + CZ reliably predicts the GEJ distance through a tunnel during POEM. It is user friendly and requires no additional resources.