Non-ablative radiofrequency (RF) application to smooth muscle of internal anal sphincter (IAS) – A tissue study

Poster presented at SAGES 2013

OBJECTIVES: Non-ablative radiofrequency smooth mus-cle remodeling has been successful in the treatment of GERD in the lower esophageal sphincter – LES (Stretta) and fecal incontinence in the IAS (Secca). This unique RF therapy has demonstrated significant improvements in barrier function without evidence of stricture. However, the precise mechanism of non-ablative RF- induced smooth muscle remodeling has been unclear.

THE AIM OF STUDY: To investigate the pathophysiologi-cal mechanisms that lead to the clinical improvement demonstrated in fecal incontinence patients following non-ablative application of radiofrequency (RF) to anal sphincters (Secca procedure).

MATERIAL: A group of 20 large white pigs, mean age 181 days, weight 160 lb. were included. All animals were housed singly in cages for the duration of the study and received pig chow and water (standard protocol). Study was performed in three groups of age and weight matched pigs: FI GROUP (6 animals underwent fecal in-continence model); FI+RF (8 pigs with FI treated with RF anal sphincter remodeling Secca procedure); CONTROL (6 pigs): no treatment. The animal experimental protocol was approved by the Animal Research Committee of Agriculture University and carried out at the same site.

METHODS: Experimental model of FI was created by pudendal nerve destruction (PND) (1,0 ml of 50% ethanol injection to pudendal nerve area under PN stimulation guidance) and lateral sphincter-otomy (LS) of external (EAS) and internal anal sphincter (IAS). FI was confirmed by anorectal ma-nometry (BAP, SAP) (Pro-Medis Sphincterometer). Six weeks after FI mod-el creation the 8 animals underwent non-ablative radiofrequency application using standard Secca protocol (64 points of RF delivery). Ten weeks after RF treatment, animals were euthanized, and anal tissues harvested for pathologic evaluation. A group of 6 age and weight matched pigs served as control.

RESULTS: Microscopic evaluation of IAS revealed characteristic circular muscle bundles separated by connective tissue septae. Thinner connective tissue fascicles wrapped individual cells. The basic architecture of the IAS was maintained following RF treatment. The amount of collagen I in the septa was statistically significantly higher than collagen III after RF. There was no significant differ-ence in the thickness of connective tissue septae between the FI RF animals and the controls. An increase in the ratio of connective tissue/ smooth muscle was ob-served in FI group, com-pared FI RF and controls. In all groups the circular muscle bundles greatly var-ied in diameter from 90 μm to 580 μm. The cross sec-tion area (CSA) occupied by SMA within the bundles increased after RF as well as the number of smooth muscle fibers within the large compartments. These bundles were separated by significantly larger septae. In FI animals IAS revealed greater percentage of con-nective tissue compared to controls. The smooth muscle layer thickness and the smooth muscle fiber density within the IAS bundles increased significantly after RF. Moreover the activity of conexin 43 increased after RF. The significant increase of smooth muscle actin within the fibroblasts after RF may suggest its differentiation towards a myofibroblast (reactive) phenotype.

CONCLUSION: Non-ablative RF application to the inter-nal anal sphincter muscle relevantly influences the struc-tural arrangement of smooth muscle and connective tissue contents. The increase of the smooth muscle fibers size and number per muscle bundles as well as the collagen I and reactive myofibroblast contents within IAS septa are potentially responsible for sphincter reinforcement and remodeling. The role of Internal Anal Sphincter conexins activity and External Anal Sphincter composition after RF application require further studies.