Tale of two tube shunt trials

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Results from recent multicenter randomized clinical trials provide evidence-based information on the safety and efficacy of aqueous shunt surgery using two widely used devices.

By Cheryl Guttman Krader; Reviewed by Steven J. Gedde, MD

Miami-Results from recent studies are providing glaucoma surgeons with valuable information to guide their use of aqueous shunts.

Steven J. Gedde, MD, reviewed the 1-year outcomes from two multicenter randomized clinical trials-the Ahmed Baerveldt Comparison (ABC) and the Ahmed Versus Baerveldt (AVB) study-that compared two aqueous shunts commonly used worldwide (Ahmed Glaucoma Valve model FP-7, New World Medical; Baerveldt Glaucoma Implant model 101-350, Abbott Medical Optics) and the 5-year results from the Tube versus Trabeculectomy study (TVT) that compared trabeculectomy with mitomycin-C (0.4 mg/ml for 4 minutes) against tube shunt surgery with the same Baerveldt device in eyes with previous ocular surgery.

The ABC and AVB studies enrolled patients undergoing tube shunt placement as a planned surgical procedure. There were 276 patients in the ABC and 238 patients in the AVB study.

“The baseline and ocular characteristics of the patient populations were very similar in the two studies,” said Dr. Gedde, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami. “The study results were also remarkably similar and served to validate each other.”

In both the ABC and AVB study, the Ahmed implant group had a lower mean IOP immediately postoperatively, but patients in the Baerveldt implant group achieved greater IOP reduction at 1 year. Analyses of adjunctive medical therapy paralleled the IOP results and showed that patients in the Ahmed group required less IOP-lowering medication early in the postoperative follow-up compared with the Baerveldt group, but the Baerveldt patients required less medication with longer follow-up.

Although the two studies differed slightly in their criteria for defining surgical success/failure, results of Kaplan-Meier survival analysis showed that the surgical success rate at 1 year was higher for the Baerveldt implant in both studies.

“Several post-hoc analyses were performed in both studies to see if the outcomes changed using different IOP criteria to define success and failure,” Dr. Gedde said. “For the ABC, when failure was defined using a very stringent criterion of IOP >14 mm Hg, the Ahmed implant had a significantly higher failure rate than the Baerveldt device.”

“Interestingly, however, in the AVB study, there were no significant differences in the treatment outcomes for the two devices when the IOP failure criteria were more stringent or less stringent than the primary outcome definition,” he said.

The safety review showed that in the ABC study, the rate of both early postoperative complications (within the first 3 months postop) and reoperation for complications was significantly higher in the Baerveldt group than in the Ahmed arm. Late postoperative complications were also more common in the Baerveldt group, but the difference versus the Ahmed arm was not statistically significant. In the AVB study, the rate of interventions done at the slit lamp or in the operating room for complications was also significantly higher in eyes with the Baerveldt implant.

TVT outcomes

The TVT study enrolled 212 patients, and early postoperative data showed IOP reduction was significantly greater in eyes having a trabeculectomy with mitomycin C versus those having tube shunt surgery. However, at 6 months and visits thereafter, IOP reduction was similar in the two study arms, showing that the two procedures resulted in similar IOP control long term, Dr. Gedde said.

Both procedures also resulted in significant decreases in the need for adjunctive mediation, but the mean number of medications needed was greater early on in eyes having the tube surgery relative to the trabeculectomy arm. Over time, the need for medications increased in the trabeculectomy eyes while it remained stable in the tube arm. At 3 years and thereafter, there were no significant differences in medication use between groups.

The TVT criteria used to define failure and success were similar to those of the ABC. By Kaplan-Meier analysis, the 5-year cumulative probability of failure was significantly higher in the trabeculectomy arm than in the tube group, 47% versus 30%, respectively.

Post-hoc analyses were also performed for the TVT study to see how changing the definitions for failure affected outcomes, and the difference favoring the tube arm persisted regardless of the criteria used.

Complications during the first month after surgery were more frequent in eyes that underwent trabeculectomy than in the tube arm, but analyses of late complications and serious complications showed no significant differences between groups.

fyi

Steven J. Gedde, MD

E: sgedde@med.miami.edu

Dr. Gedde has no financial interest in the subject matter. This article is based on Dr. Gedde’s presentation at the 2012 annual meeting of the American Academy of Ophthalmology.