350. FUNCTIONAL RESPONSES OF SWINE ESOPHAGUS TO FOCAL CRYOTHERAPY

Abstract

Barrett’s esophagus is a premalignant condition where the squamous epithelium of the distal esophagus is replaced by columnar epithelium. Treatment involves endoscopic resection followed by ablation for complete eradication. Various ablative techniques exist including cryotherapy which utilizes a cryogen spray or balloon catheter. While efficacious, complications such as dysphagia have been reported. To better understand the underlying mechanism of how cryotherapy might damage the muscularis, isolated muscle strips were ablated and their function studied.

Isolated muscle strips with the mucosa layers removed were prepared from freshly isolated swine esophagus and placed in tissue baths where they were electrically stimulated, and contractile forces were recorded. Contractile responses were allowed to stabilize before a given muscle strip was removed for focal ablation. Cryoablation was performed with a focal cardiac ablation catheter (Freezor, Medtronic). Following ablation, the given muscle strip was returned to the tissue baths. Regression analyses were performed using temperature data from a thermocouple integrated into the tip of the ablation catheter and contractile forces after the esophageal muscle strips had recovered for 3 hours.

Ablations lasting less than 60 seconds were applied to 135 esophageal muscle strips: with an average mass of 94 mg. From the experimental data, a multiple linear regression model was generated: 71.93 + 0.4770x—0.5530y = z, where x is the minimum temperature (C), y is the time below 0 C, and z is the contractile force (normalized to preablative force, %). Our model has an adjusted R-squared value of 0.508. As expected, lower minimum temperatures and longer treatment times were associated with greater losses in stimulated muscle forces.

We were able to reproducible ablate isolated swine esophageal strips that elicited contractile responses in vitro. Lower temperatures and longer treatment times were associated with greater losses in stimulated muscle forces. Yet, the adjusted R-squared value indicates that temperature and time only partially explain the response. Future studies could be improved by accounting for variabilities in sample sizes and additionally, regression diagnostics need to be performed to check for outliers and validate model assumptions.