Characterization of micro-invasive trabecular bypass stents by ex vivo perfusion and computational flow modeling.

Micro-invasive glaucoma surgery with the Glaukos iStent® or iStent inject® (Glaukos Corporation, Laguna Hills, CA, USA) is intended to create a bypass through the trabecular meshwork to Schlemm's canal to improve aqueous outflow through the natural physiologic pathway. While the iStent devices have been evaluated in ex vivo anterior segment models, they have not previously been evaluated in whole eye perfusion models nor characterized by computational fluid dynamics. Intraocular pressure (IOP) reduction with the iStent was evaluated in an ex vivo whole human eye perfusion model. Numerical modeling, including computational fluid dynamics, was used to evaluate the flow through the stents over physiologically relevant boundary conditions. In the ex vivo model, a single iStent reduced IOP by 6.0 mmHg from baseline, and addition of a second iStent further lowered IOP by 2.9 mmHg, for a total IOP reduction of 8.9 mmHg. Computational modeling showed that simulated flow through the iStent or iStent inject is smooth and laminar at physiological flow rates. Each stent was computed to have a negligible flow resistance consistent with an expected significant decrease in IOP. The present perfusion results agree with prior clinical and laboratory studies to show that both iStent and iStent inject therapies are potentially titratable, providing clinicians with the opportunity to achieve lower target IOPs by implanting additional stents.

Second-generation trabecular meshwork bypass stent (iStent inject) increases outflow facility in cultured human anterior segments.

PURPOSE: To determine whether a second-generation trabecular meshwork (TM) bypass stent (iStent inject) influences outflow facility in cultured human anterior segments. DESIGN: Prospective laboratory investigation using normal human donor eyes. METHODS: Human anterior segments (n = 7) were placed in perfusion organ culture. One or 2 iStent inject stents were inserted into the TM within the nasal and/or superior quadrants using a specially designed injector. Anterior segments were returned to culture and perfused for an additional 24 hours. Morphology of the TM and Schlemm canal (SC) was assessed by scanning electron microscopy (SEM) and 3-dimensional micro-computed tomography (3D micro-CT). RESULTS: Insertion of 1 iStent inject into the nasal or superior quadrant of the TM increased outflow facility from 0.16 ± 0.05 µL/min/mm Hg to 0.38 ± 0.23 µL/min/mm Hg (P < .03, n = 7), with concurrent pressure reduction from 16.7 ± 5.4 mm Hg to 8.6 ± 4.4 mm Hg. Addition of a second iStent inject further increased outflow facility to 0.78 ± 0.66 µL/min/mm Hg (n = 2). SEM showed the iStent inject flange compressed against the uveal region of the TM, the thorax securely inserted within the TM, and the head located in the lumen of SC. Dilation of SC was noted around the iStent inject head and SC cell disruption was observed at the iStent inject insertion site. 3D micro-CT confirmed iStent inject placement. CONCLUSION: iStent inject, a second-generation bypass stent, increased outflow facility in human anterior segment culture. The iStent inject is a promising new device to lower intraocular pressure via TM bypass.

Histologic evolution of high-intensity focused ultrasound in rabbit muscle.

RATIONALE AND OBJECTIVES: The purpose of this study was to examine the histologic evolution over time of rabbit skeletal muscle thermally ablated with high-intensity focused ultrasound. The objectives included determining the extent and focality of damage created by this noninvasive, transcutaneous ablative technology. METHODS: Transcutaneous, thermal ablation with an external focused ultrasound transducer was applied to the paraspinous muscles of 19 rabbits. At varying times, up to 100 days after therapy, single sonications were examined histologically. RESULTS: Initially, only subtle staining changes were identified within lesions. In the chronic phase (day 51-100), the muscle was replaced or infiltrated by variable amounts of scar and fat similar to degenerative muscle disorders. Histologic changes were limited to the tissue within the intensity focus of the transducer and were not seen in intervening tissues. DISCUSSION: The current study took a systematic approach to study the long term, in vivo histologic effects of single HIFU lesions in a nonregenerative tissue. This experience in muscle tissue will provide a basis for understanding ultrasound effects for clinical applications such as treatment of uterine fibroids, cardiac tissue, and sarcomas.

Initial experience with a novel focused ultrasound ablation system for ring ablation outside the pulmonary vein.

INTRODUCTION: Atrial fibrillation has been shown to initiate from triggers within pulmonary veins. Several studies have documented that electrical isolation of those triggers can lead to maintenance of sinus rhythm. The complication of pulmonary vein stenosis has limited the utility of delivering ablation energy within the pulmonary vein. We utilize a focused ultrasound catheter ablation system for delivery of transmural ablation lines proximal to the pulmonary vein ostium. METHODS: Nine dogs (weight 30-39 kg) were anesthetized and ventilated. Through a transseptal approach, pulmonary veins were engaged with the focused balloon ultrasound catheter. Ultrasound power was delivered at 40 acoustic watts outside the pulmonary vein ostium, focused 2 mm off the balloon surface, with a depth of approximately 6 mm, for 30-120 seconds. Following ablation, lesions were histopathologically analyzed. RESULTS: Of nine animals studied, fourteen pulmonary veins were ablated. We found successful delivery of near circumferential and transmural ablation lines in 6/14 pulmonary veins. In each of the six circumferential ablations, successful alignment of the ultrasound transducer along the longitudinal axis of the parabolic balloon occurred. The final four ablations were conducted with an enhanced catheter design that assured axial alignment. Of these ablations, all four were circumferential. The remaining 8 pulmonary veins had incomplete delivery of lesions. In each of these veins the ultrasound transducer was misaligned with the balloon axis when therapy was delivered. CONCLUSION: Focused ultrasound ablation is a new means of performing pulmonary vein isolation. This method provides delivery of lesions outside the vein, limiting the risk of pulmonary vein stenosis for the treatment of atrial fibrillation.