Occlusion of acquired renal arteriovenous fistula with transcatheter electrocoagulation

Enhanced occlusion of vessels combining retrievable, detachable coils as differential electrodes with percutaneous, intravascular radiofrequency electrocoagulation. An experimental study

RATIONALE AND OBJECTIVES

The authors evaluate the feasibility to accelerate occlusion of high-velocity flow vessels by a combination of transcutaneous coil placement and application of radiofrequency current.

METHODS

Piglets (n = 8) were anesthetized and acutely instrumented via cutdowns in both carotid and one brachial arteries. Two identical cylindrically shaped coils (length, 3 mm; outer diameter, 2.4 mm; inner diameter, 1.4 mm) were mounted on titanium-nickel core wire and placed via 3-French Nylon catheters in both iliac arteries. The coils were kept connected to the delivery wire, which is isolated from the surrounding tissue by the catheter. The first-placed system served as control, the contralateral coil was connected to a radiofrequency generator closing electrical circuit via an external indifferent electrode. Angiograms via the brachial artery demonstrated the adequate placement of the coils and the status of the iliac arteries without and with current application. In 6 of the 8 cases, 25 watts of radiofrequency current were applied repeatedly over 10 seconds to the coil on one side at 4-minute intervals until occlusion was demonstrated. In 2 of 8 cases. 25 watts were applied continuously over 30 seconds. The coils were detached from the wire the catheters removed. Additional angiograms were performed after 5, 15, 45, and 60 minutes to show the patency of the control setting.

RESULTS

Complete occlusion was achieved in all cases after a maximum of three consecutive applications of current for 10 seconds. The control remained patent for a minimum of 45 minutes. On gross and histologic examination the arteries on both sides remained intact. Disruption and charring occurred only after continuous application of current over 30 seconds.

CONCLUSIONS

It is feasible to use detachable coils in conjunction with high-frequency electrocoagulation to promote coil fixation and accelerate occlusion of vessels with high blood flow.

Experimental evaluation of a new instrument for transcatheter electrocoagulation

A new coaxial electrode catheter design has been tested in 19 renal arteries of pigs with excellent results, i.e. 100 per cent thrombosis. One vessel ruptured. The electrode (anode) is situated on a thin inner catheter and after electrolysis it is pulled back into a shielding outer catheter. This should reduce downstream embolization. Usual currents have been 8 to 10 mA at 10 V and doses of 16 to 36 C have been used depending on the size of the artery. In the single case of rupture of the vessel a current of 20 mA was used. The method appears to be ready for clinical testing.

Evaluation of the anode and cathode for transcatheter electrocoagulation

The effect of changing the size and position of the anode and cathode during direct current Transcatheter Electrocoagulation (TCEC) was evaluated in dogs. The results showed that there was no difference in the time required for vessel occlusion when the size and position of the electrodes were changed. However, there were differences noted in the amount of voltage needed to maintain the constant current. Based on these results, for TCEC we recommend positioning the largest possible guidewire anode against the vessel wall. The cathode should be a highly lubricated sponge covered Bovie ground plate.

Transcatheter embolization of traumatic renal arteriovenous fistula

An iatrogenic renal arteriovenous fistula was treated by transcatheter embolization with particles of absorbable gelatin sponge. Recurrent massive hematuria was successfully controlled. The procedure was easily accomplished with minimal loss of renal parenchyma. Surgery, which usually requires partial or total nephrectomy, was avoided.

Vessel occlusion with transcatheter electrocoagulation

Transcatheter intravascular electrocoagulation for therapeutic occlusion of vessels has been experimentally developed and successfully used clinically as an alternative to, and in conjunction with, more routine methods of vessel occlusion. A constant current power source and a steelguide wire anode are used for the occlusion. The subject is grounded with a standard bovie plate insulated from the skin by a highly lubricated sponge. Permanent occlusion of strategic vessels at accurately controlled sites has been achieved with little risk of embolization of non-target areas. There has been minimal damage to vessel walls, and complete occlusion has been possible despite heparinization and/or thrombocytopenia. One limitation is the inconstant ability to position the anode precisely at the desired site of occlusion. Also, a long time may be required (up to one hour) to occlude larger vessels with presently available anodes. Wider use must await refinements in development of the anode material and in its delivery system.