Chapter 46 RADIOFREQUENCY TREATMENT FOR THE MANAGEMENT OF GENUINE STRESS URINARY INCONTINENCE

Genuine stress incontinence (SUI) affects a substantial and increasing proportion of the female population.¹^–⁴ It is well accepted that SUI is often associated with substantial quality-of-life disruption and desire on the part of the sufferer for improvement in or resolution of attendant symptomatic bother. A recent outcomes analysis suggested that women seeking therapy for genuine SUI would accept symptom improvement as an important and positive outcome aspect even if cure were not obtained.⁵ The referral and usage trends for surgical interventions such as colposuspensions and suburethral slings suggest that, for women with less advanced symptoms, factors including patient fear or reluctance about surgical morbidity rates, recovery times, and other lifestyle concerns cause these procedures to be employed in a relatively small percentage of the overall affected population.^2,^6,⁷ In addition, despite minimal invasiveness and positive safety profiles, nonsurgical modalities have in many cases been plagued with unfavorable compliance rates and chronic treatment requirements, as well as questionable effectiveness and durability.^8,⁹

For the large population of less symptomatically bothered patients who desire treatment for their condition, the application of radiofrequency (RF) energy to the endopelvic fascia has been proposed as a new category of less invasive, first-line surgical intervention. In other disciplines, RF microremodeling has been shown to be well suited for the treatment of disorders characterized by the inappropriate passage of luminal contents through a dysfunctional anatomic and/or physiologic barrier, for example in fecal incontinence ¹⁰ and gastroesophageal reflux disease.¹¹ The RF energy procedure aims to treat genuine SUI by correcting the laxity and elasticity of the fascial “hammock”¹² supporting the urethra and bladder neck via thermally induced tissue shrinkage and contraction.¹³ Specific heating of the endopelvic fascia denatures collagen fibers, causing acute contraction (shrinkage) of the treated tissue while also stimulating a fibrotic response.¹⁴ In subsequent weeks, collagen in-growth and scar tissue formation further shrink and stabilize the endopelvic fascia, reducing its compliance to intra-abdominal pressure increases and stabilizing the position of the bladder neck.¹⁵ This summary introduces the theoretical principles behind RF treatment of genuine SUI and reviews available literature describing approaches and results of currently available RF modalities.

THEORETICAL PRINCIPLES

The pathophysiology of genuine SUI is generally attributed to loss of passive support of the urethra due to tissue injury, stretching, or loss of stability, and/or lack of functioning neurologic control of the muscles of the pelvic floor and urethra.^12,¹⁶^–¹⁸ Passive support weakness may provide inadequate support to the urethra, resulting in urethral hypermobility and poor urethral compression during stress events and periods of increased physical activity, leading to urine leakage.¹⁹^–²¹ A compounding effect of passive support failure is displacement of the urethra, which results in unequal distribution of sudden intra-abdominal pressure to the bladder and urethra, with the bladder pressure overcoming the pressure within the descended urethra, thereby further contributing to episodes of uncontrolled urine loss.

Developers of RF treatment hypothesized that if the collagen-rich endopelvic fascia in women with genuine SUI could be shrunk, and thus stabilized, through a direct application of controlled heat, these non-neurologic continence mechanisms could be positively affected and continence restored. It was envisioned that this could be accomplished via a minimally invasive approach with a very low associated risk of surgical complications.

ENERGY-TISSUE INTERACTIONS

The ability of heat to effect shrinkage of collagen-containing tissue is a function of several characteristics of the collagen molecule, which is triple-helical and fibrillar in structure. The intramolecular hydrogen bonds, or cross-links, that maintain the triple-helical configuration are thermally labile, whereas the intermolecular bonds that maintain the fibrillar structure are thermally stable. Heat in the range of 60°C to 80°C will disrupt the intramolecular cross-links, causing the helix to unwind, while the heat-stable fibrillar structure remains intact. This results in shrinkage on the longitudinal axis along with swelling of the fibrils.¹³

The clinical use of RF energy to achieve tissue shrinkage via collagen denaturation is well documented in the literature.^13,²²^–²⁵ In this context, RF energy is applied to the tissue via direct contact with electrodes, and tissue heating occurs as the tissue resists the flow of the RF current. Heat conducts from high to low temperature regions in the tissue, creating a three-dimensional thermal effect. This thermal effect is specific to the amount of RF energy delivered, the tissue resistance, and the electrode configuration.

These concepts were modeled after studies demonstrating tissue shrinkage via RF energy. Hecht and colleagues described the use of monopolar RF energy to treat bovine joint capsular tissue in vivo.¹³ They found that the application of RF energy was followed by tissue reaction and concomitant degradation of collagen with the ensuing build-up of new collagen over a 12-week period, resulting in remodeling of the joint capsular tissue. The primary treatment effect was heat-induced tissue shrinkage associated with the denaturation of collagen; maximal shrinkage occurred at temperatures ranging from 60°C to 80°C. Posttreatment histologic evaluation revealed that thermal effects were localized to the region of RF energy application. Subsequent evaluations showed a tissue healing response characterized by fibroblast and capillary proliferation that ultimately resulted in complete tissue healing at 12 weeks. Chen and associates performed a series of experiments on fresh bovine heart tendons.²⁶ The tissue was mounted in a tension-free holder, and the amount of shrinkage was measured as a function of time and temperature. The study showed that maximal tissue shrinkage occurred only if the thermal treatment time and temperature exceeded a certain threshold. Notably, a temperature of 70°C effected near-maximal shrinkage when applied for a minimum of 30 seconds. Temperatures lower than 70°C demonstrated significantly diminished capacity for effective shrinkage regardless of the duration of the heat application. This information was used to develop an RF energy treatment algorithm for shrinking the endopelvic fascia to restore continence in women with genuine SUI.