RF Thermal Energy Systems

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Background

RF ablation techniques are not new to medicine. RF energy has been used over the decades to treat a variety of medical disorders ranging from tumor ablation to accessory A-V pathway disruption in patients with Wolff-Parkinson-White Syndrome. The effects of Stretta RF on the GEJ are incompletely elucidated to date but appear to be a combination of focal tissue remodeling and/or afferent vagal neurolysis.

Earlier studies to determine the effect of RF energy on tissue alteration in the GEJ were performed on porcine and canine models. Histopathic assessment was inconclusive in the pig study whereas the dog model demonstrated marked muscle hypertrophy and fibrosis (Utley et al, 2000). Segments of tissue from the gastric cardia showed a significant increase in thickness after RF energy delivery. However, an endoscopic ultrasonogram (EUS) study in a small group of patients performed prior to and 6 months following RF treatment showed no significant alteration in the wall thickness in the GEJ region (Dibaise et al, 2002).

A second potential mechanism for RF effect may be disruption of the vagal mechanosensory mechanism, which triggers tLESrs (ie, neurolysis). Human studies have shown a significant reduction in the frequency of distention-induced tLESrs at 3 and 6 months in a group of 20 patients following Stretta treatment (Tam et al, 2003). The postprandial tLESr rate diminished from a mean of 6.8 to 5.2 per hour during a 3-hour postmeal recording period. In this study, it should be noted that the RF energy delivery to the cardia was more intense than currently recommended. A most recent preliminary report suggests RF energy may also effect sensory factors in the GEJ zone (Ark et al, 2003). A group of 13 patients were examined before and 3 and 6 months after RF treatment for GERD. The Bernstein acid perfusion test (infusion of 0.1 HCl into the mid-esophagus for 30 minutes) was performed as part of the investigation. Before RF treatment all patients had a positive symptomatic response during the acid infusion test. Six months after RF therapy, 4 patients became insensitive to acid infusion, and the mean time before symptoms were experienced by the patients during acid infusion was prolonged significantly from 9 ± 6 to 17 ± 1 minutes.

Device:Stretta System

Curon Medical Inc (Sunnyvale, CA) received approval from the FDA to market the "Stretta System" for treatment of

GERD in April 2000. The Stretta System consists of a 4-channel control module generator for automated modulation of RF energy output while constantly monitoring tissue temperature and the RF delivery catheter. The circuitry is completed by an electrode pad applied to the back and connected to the control module.The catheter RF delivery component consists of a distal inflation balloon covered by 4 electrode strips or sheaths positioned radially at 90° increments. (The catheter system can be continuously irrigated with water during RF energy delivery from ports adjacent to the needle entry sites.) Within each delivery sheath is a curved 5.5 mm needle electrode that is deployed into tissue during balloon distention. During the flow of RF current between the needle and surrounding tissue, thermocouples in the base and tip of the nickel-titanium catheters provide constant feedback information to the control module about the tissue temperatures. The computerized control algorithm continuously ensures optimal target tissue temperature of 85°C at the electrode tip and below 50°C at the mucosa. This provides spherical thermal lesions in the tissue surrounding the tip while the overlying mucosa remains relatively unaffected by RF injury.

Procedure

Anatomic distances from the squamocolumnar junction (SCJ) to the incisor teeth are obtained at initial endoscopic examination. Following placement of a guidewire, the endoscope is removed and the Stretta catheter is inserted over the wire and positioned 1 cm above the SCJ based on the interval markings on the shaft of the instrument relative to the electrode sites. The electrodes are deployed during balloon inflation (2.5 psi) into the muscle of the GEJ. RF energy is delivered for 90 seconds; reduction in the electrode impedance is displayed on the consul screen as the electrodes penetrate into muscle. Following completion of the initial set of lessons, the balloon is deflated, the needles retracted, and the catheter is rotated 45°. A second set of lesions are made in the same axial plane establishing a circular ring of 8 RF thermal burns. Three additional rings are created in a similar manner at 0.5 cm above the SCJ, at the SCJ, and 0.5 cm below. Following this, the catheter is inserted into the stomach, the balloon is inflated to 25 cc and the ensemble is retracted against the hiatus and the electrodes are deployed once again. Two "pull-back" rings of 12 lesions are formed subsequently in the cardia. Optimally, 14 lesion sets (56 RF sites) are delivered during a total of 21 minutes of active RF therapy (Figure 13-2).

In the initial open-label report of 47 patients treated with the Stretta procedure, conscious sedation involved midazolam (mean 6.7 mg; range 2.0 to 13.5) and either fentanyl (mean 13.4 mg; range 75 to 275) or meperidine (mean 114 mg; range 12.5 to 300). Multiple lesion sets were created (mean 13.8 ± 2.5) with a mean total procedure time

Gerd Stretta Ablation
FIGURE 13-2. Stretta System (Curon Medical Inc, Sunnyvale, CA) radiofrequency thermal energy system.

of 69 ± 17 minutes. In this report, the RF energy delivery time was 52 ± 10 minutes (Triadalfilopoulos et al, 2001).

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