Endoluminal thermal occlusion of the ureter with the electromagnetic field-focusing device

In Vitro Evaluation of the Occlusive Properties of the ArtVentive Endoluminal Occlusion System Occlusion Device for Transrenal Ureteral Occlusion

PURPOSE

Current techniques for percutaneous ureteral occlusion are either technically difficult or not satisfactory because of frequent ureteral recanalization. The purpose of this in vitro study was to evaluate the occlusive properties of an "off the shelf" solution (Endoluminal Occlusion System [EOS™]; ArtVentive Medical Group, Inc., Carlsbad, CA) for transrenal ureteral occlusion.

MATERIALS AND METHODS

Both 8 and 11 mm expanded polytetrafluoroethylene-covered ArtVentive EOS devices were used in 10 porcine models. Experiments were performed in explanted porcine ureters to simulate physiologic conditions. EOS devices were deployed in a midureteral position using a transrenal approach. Contrast agent (Iopamidol 300) diluted in saline solution was infused into the renal pelvis under continuous fluoroscopic guidance. Intrapelvic pressure measurements were performed until leakage, plug dislocation, or until pelvic blow out occurred.

RESULTS

All EOS devices were deployed effectively and achieved prompt total ureteral occlusion. Ureteral leakage occurred with intraureteral pressures between 60 to 109 cm H₂O (8 mm EOS) and between 65 and 125 cm H₂O (11 mm EOS). Before leakage, tubular reflux was seen in all cases, pelvic blowout occurred in half of the cases.

CONCLUSIONS

The ArtVentive EOS occlusive device is an effective tool for "off the shelf" ureteral occlusion. Both the 8 mm and the 11 mm devices fully occluded ureters at pressure levels that are to be expected in vivo.

MR Coagulation: A Novel Minimally Invasive Approach to Aneurysm Repair

PURPOSE

To demonstrate a proof of concept of magnetic resonance (MR) coagulation, in which MR imaging scanner-induced radiofrequency (RF) heating at the end of an intracatheter long wire heats and coagulates a protein solution to effect a vascular repair by embolization.

MATERIALS AND METHODS

MR coagulation was simulated by finite-element modeling of electromagnetic fields and specific absorption rate (SAR) in a phantom. A glass phantom consisting of a spherical cavity joined to the side of a tube was incorporated into a flow system to simulate an aneurysm and flowing blood with velocities of 0-1.7 mL/s. A double-lumen catheter containing the wire and fiberoptic temperature sensor in 1 lumen was passed through the flow system into the aneurysm, and 9 cm³ of protein solution was injected into the aneurysm through the second lumen. The distal end of the wire was laid on the patient table as an antenna to couple RF from the body coil or was connected to a separate tuned RF pickup coil. A high RF duty-cycle turbo spin-echo pulse sequence excited the wire such that RF energy deposited at the tip of the wire coagulated the protein solution, embolizing the aneurysm.

RESULTS

The protein coagulation temperature of 60°C was reached in the aneurysm in ∼12 seconds, yielding a coagulated mass that largely filled the aneurysm. The heating rate was controlled by adjusting pulse-sequence parameters.

CONCLUSIONS

MR coagulation has the potential to embolize vascular defects by coagulating a protein solution delivered by catheter using MR imaging scanner-induced RF heating of an intracatheter wire.

In vitro evaluation of the occlusive properties of latex-covered amplatzer vascular plugs for transrenal ureteral occlusion

PURPOSE

To evaluate the occlusive properties of latex-covered Amplatzer Vascular Plugs (AVPs) for transrenal ureteral occlusion in vitro.

MATERIALS AND METHODS

Latex-covered AVPs type I and II (diameter 8, 10, 12, 14, and 16 mm) were used as occlusive devices. Radial force of an AVP was measured using simulated ureteral diameters of 4 to 12 mm. Occlusive properties were examined in a silicone tube (inner diameter 6 mm) with measurement of drainage time of a 40 cm water column. In complete occlusion, the maximum pressure that the plug was able to withstand was determined at different temperature levels. Statistical analysis of drainage time was performed in a general linear model (GLM) and using correlation analyses. Explanted porcine ureters were used to simulate physiologic conditions. Pressure measurements were performed until leakage, plug dislocation, or rupture of the ureter occurred.

RESULTS

Radial force depended on AVP type, size, ureteral diameter, and temperature. The 16-mm AVP II showed the highest radial force of more than 5 N (ureteral diameter 4 mm, body temperature). All AVP I showed water leakage and plug dislocation. Drainage time of the AVP II depended significantly on plug size and temperature and correlated with radial force (r=0.731, P<0.001). In complete occlusion, water leakage occurred at 500 to 1000 cm H2O and dislocation between 500 to more than 2000 cm H2O. In porcine ureters, leakage occurred at room temperature between 19 to 93 cm H2O. At body temperature, all AVP II occluded the ureter completely.

CONCLUSION

Latex-covered AVP II (diameter 8-16 mm) can effectively occlude the ureter, especially considering remodeling of the nitinol at body temperature. Large plug diameters can exert enough radial force even in dilated ureters to allow for successful occlusion. Because deployment of a 16-mm latex-covered AVP II can be technically difficult, we advocate the use of 12- or 14-mm AVP II for transrenal ureteral occlusion. AVP Is are not suitable for ureteral occlusion.