Intraoperative FLIP distensibility during POEM varies according to achalasia subtype

Background The functional luminal imaging probe (FLIP) can be used to measure the esophagogastric junction distensibility index (DI) during myotomy for achalasia and increased DI has been shown to predict superior clinical outcomes. The objective of this study was to determine if the intraoperative DI and the changes produced by per oral endoscopic myotomy (POEM) differed between achalasia subtypes. Methods FLIP measurements were performed during POEM for achalasia at a single institution. DI (defined as the minimum cross-sectional area (CSA) at the EGJ divided by distensive pressure) was measured at three time points: after induction of anesthesia, after submucosal tunneling, and after myotomy. Measurements were reported at the 40 mL fill volume for the 8 cm FLIP (EF-325) and at the 60 mL fill volume for the 16 cm FLIP (EF-322). Measurements were compared using chi-square and Kruskal–Wallis tests. Results 142 patients had intraoperative FLIP performed during POEM for achalasia between 2012 and 2019 (30 type I, 68 type II, 27 type III, and 17 variant). Patients with type I achalasia had a significantly higher induction DI (median 1.7 mm 2 /mmHg) than type II (0.8 mm 2 /mmHg), type III (0.9 mm 2 /mmHg), and variants (1.1 mm 2 /mmHg; p < 0.001). These differences persisted after submucosal tunneling and final DI after myotomy was also significantly higher in type I patients (median 8.0 mm 2 /mmHg) compared to type II (5.8 mm 2 /mmHg), type III (3.9 mm 2 /mmHg), and variants (5.4 mm 2 /mmHg; p < 0.001). Achalasia subtypes were found to have similar CSA at all time points, whereas pressure differed with type I having the lowest pressure and type III the highest. Conclusion The DI at each operative step during POEM was found to differ significantly between achalasia subtypes. These differences in DI were due to pressure, as CSA was similar between subtypes. Achalasia subtype should be accounted for when using FLIP as an intraoperative calibration tool and in future studies examining the relationship between DI and clinical outcomes.