EFFECT OF CHANGE IN ESOPHAGOGASTRIC OPENING PARAMETERS ON FUNCTIONAL LUMINAL IMAGING PROBE (FLIP) IN PER-ORAL ENDOSCOPIC MYOTOMY (POEM) IN TREATMENT OF TYPE I AND II ACHALASIA ON SYMPTOMATIC OUTCOME

BACKGROUND:
Despite high success rates of per-oral endoscopic myotomy (POEM) in treatment of achalasia, many patients continue to experience symptoms. Utilization of functional luminal imaging probe (FLIP) during POEM has allowed for real-time assessment of myotomy adequacy. While studies have demonstrated association of symptoms with EGJ opening parameter thresholds after achalasia therapy, there is little data on the association of the change in EGJ opening parameters pre- and post-POEM with symptomatic outcomes. The aim of this study was to compare symptomatic outcomes after POEM based on change in EGJ opening parameters.

METHODS:
36 patients with type I/II achalasia underwent POEM with intra-procedural 16 cm length FLIP balloon with intra-POEM EGJ distensibility index (DI) threshold of ≥2.8mm²/mmHg for completion. Distensibility index (DI) was assessed at 60ml. Max EGJ-diameter (EGJ-D) was assessed at 70ml fill volume. Symptomatic outcome using Eckardt score (ES) was evaluated comparing pre-POEM and 6-month post-POEM EGJ opening on FLIP. %ΔDI was calculated via: (post POEM DI - pre POEM DI)/(pre POEM DI) x 100%. Cohorts were stratified by pre-POEM DI and EGJ-D. POEM success was defined as ES ≤3.

RESULTS:
36 patients were evaluated, mean (SD) age 51.2 (5.3) years old, 36% with type I achalasia. Mean (SD) pre-POEM DI was 1.2 (0.2) mm²/mmHg and mean (SD) pre-POEM EGJ-D was 10.4 (0.5) mm. Post-POEM mean (SD) DI increased to 4.8 (0.7) mm²/mmHg (p<0.01). Post-POEM, 17% (n=6) had DI <2.8 mm²/mmHg; 5% (n=2) had a post-POEM EGJ-D < 13mm. Mean pre-POEM to post-POEM ΔDI was an increase of 3.7 (0.7) mm²/mmHg, with an average %ΔDI increase of 373%. Post-POEM success achieved in 83% (n=29). (TABLE 1)

The largest change in EGJ opening pre- to post-POEM was in patients with pre-POEM DI <1 mm²/mmHg with mean %ΔDI increase of 434%. This was followed by patients with pre-POEM DI 1-2 mm²/mmHg and patient with pre-POEM DI >2 mm²/mmHg at %ΔDI increase of 292% and 134%, respectively (p<0.01). With EGJ-D, pre-POEM DI <1 mm²/mmHg saw mean %ΔEGJ-D increase of 88%, which was similar to %ΔEGJ-D in the pre-POEM DI 1-2 mm²/mmHg group increase of 70% (p=0.18), but increased relative to pre-POEM DI >2 mm²/mmHg group with an increased diameter of 29% (p<0.01). Post-POEM, success rates did not differ between patients regardless of degree in change in EGJ opening on FLIP (TABLE 2).

DISCUSSION:
Relative change in FLIP EGJ opening parameters pre- to post-POEM showed no difference on symptomatic outcome following POEM when all patients achieved an intra-procedural DI ≥2.8mm²/mmHg. Therefore, an absolute threshold of intra-operative DI of ≥2.8mm²/mmHg is sufficient to predict symptomatic outcome. Additional mechanisms of treatment failure other than incomplete myotomy including aperistalsis, anatomical deformities and buried spasm need to be evaluated in future studies.