Percutaneous Management of Thrombosis in Native Hemodialysis Shunts



Percutaneous Management of Thrombosis in Native Hemodialysis Shunts


Dierk Vorwerk



Clinical Relevance


Percutaneous procedures for hemodialysis shunts are becoming increasingly important for interventional radiologists. A growing number of patients with renal insufficiency are enrolled in dialysis programs, the majority of them undergoing hemodialysis. In the West, this affects some 150 to 200 persons per million inhabitants. Given the increase in patients’ life expectancy, maintaining access to the vascular system continues to be a problem.1 For example, the number of long-term functioning shunts is estimated to be 15%.1 Primary patency of hemodialysis shunts is low: approximately 65% of Brescia-Cimino shunts and 50% of polytetrafluoroethylene (PTFE)-covered shunts exhibit primary patency after 1 year, and the numbers sink after 2 and 4 years to 60% and 45% for Brescia-Cimino shunts and to 43% and 10% for PTFE-covered shunts.1


In Europe, arteriovenous Brescia-Cimino shunts are the preferred primary shunts, used in conjunction with the radial artery and veins of the lower arm. Autologous veins in the proximal lower arm and elbow region are generally preferred even for renewed shunt application. For percutaneous revascularization, the choice of access site, indications, and interventional technique employed depend on the nature and location of the shunt, site of the lesion, and nature of the obstruction.


Shunt thrombosis of native fistulas is a complication not as frequent as in grafts.1 Besides an underlying stenosis that is present in almost all cases, cofactors are manifold: clotting abnormalities, thrombocytosis, disturbed fluid balance, hypotension, and aneurysmatic degeneration of the native vein causing low flow may lead to shunt thrombosis. There are, however, different types of shunt thrombosis that require different strategies of percutaneous intervention.



Indications


Indications for interventional treatment are acute or subacute occlusions in native fistulas that prevent use of the arteriovenous connection for dialysis. Relative indications are occluded fistulae in patients with a functioning renal allograft. Percutaneous intervention is contraindicated in acute infections of the vein or perivenous space. It is, however, worth trying to recanalize even thrombosed immature fistulas because there is a good chance of restoring flow and allowing development of a mature fistula after percutaneous recanalization.2,3 Natario et al. achieved clinical success in immature fistulas in 97%, with a 1-year primary patency of 51%.3 Miller et al. achieved 85% technical success in thrombosed immature fistulas, 79% clinical success, and a secondary patency of 90% at 12 months.2



Clinical Situation


Clinical examination of the shunt and especially palpation of the venous outflow tract gives an impression of the type of occlusion and its location and is an inevitable part of the clinical checkup prior to an intervention. When in doubt, sonography and duplex sonography may help determine the extent of a thrombosis and its location.


Shunt occlusions in Brescia-Cimino fistulas, especially in the very early phase, may be due to only a very short plug-like thrombus selectively obstructing the arteriovenous anastomosis or a segment of the venous outflow. In those cases, the draining shunt vein is soft and compressible at palpation. If digital manipulation to remove the thrombus fails, this type of obstruction is an ideal candidate for percutaneous transluminal angioplasty (PTA), since the small thrombus can be macerated by balloon inflation alone, and flow can be restored immediately. Treatment, however, should be started soon to avoid propagation of thrombosis.


Palpation also detects those cases where shunt thrombosis is due to an underlying severe stenosis and a subsequent small thrombus formation. If this happens close to the arteriovenous anastomosis, the amount of thrombus is usually small, and balloon dilatation alone may be sufficient for recanalization and treatment of the underlying stenosis.


Long-segment thrombosis of Brescia-Cimino fistulas present with enlarged and incompressible veins that appear rather hard during palpation. PTA alone is mostly insufficient in these cases.


Very rarely, arterial thrombosis or embolism may be a cause for shunt dysfunction. Percutaneous treatment depends on the location and amount of thrombus that has to be removed. It can vary from simple PTA to thrombolysis.





Technique


Anatomy and Approaches


The anatomy of native hemodialysis fistulas is very individual and may alter due to current arterialized blood stream, pressure, and traumatization. There are some principal forms of fistula that determine which access to the thrombosis is appropriate.



Native Lower Arm Shunts


As a rule, venous access is chosen for Brescia-Cimino shunts. The shunt vein is punctured with the patient wearing a compression bandage. A large-lumen cannula can be employed for the puncture if the vein is large and well palpable, and a regular guidewire (0.035 inch in diameter) can be inserted. However, the micropuncture procedure is recommended if the lumen of the vein is narrow and poorly palpable; in this case, the vein is punctured with a 22-gauge needle and a 0.018-inch wire is inserted. Subsequently, a 16-gauge plastic cannula containing a sharp-pointed needle is inserted into the shunt vein coaxially while being rotated. To prevent it from breaking, imaging must confirm that the thin wire does not suddenly kink. If the position of the plastic cannula is secure, the stylet and guidewire should be replaced by a 0.035-inch wire. A hydrophilically coated wire is well suited.


Retrograde puncture is performed in lesions near anastomoses (i.e., distal venous lesions), stenotic anastomoses, and distal arterial stenoses.


Antegrade transbrachial arterial access as a “backdoor” entrance may be necessary in exceptional cases if the operator does not succeed in probing a stenosis or occlusion near the anastomosis via a venous access. In this case, the brachial artery is punctured in an antegrade manner at the level of the elbow joint, and after thorough probing of the artery supplying the shunt—normally the radial artery—a 4F catheter is inserted. The stenosis is overcome using the wire and catheter, and the wire is then guided out via the venous puncture site as a pull-through approach. The intervention is then performed via the venous site to avoid over-enlarging the arterial puncture.


For occlusions in the proximal segments of the draining veins, the shunt vein is punctured antegrade at a peripheral puncture site. If a proximal lesion cannot be probed via the peripheral access, or if probing is prevented by a dissection or perforation, there is still the option of attempting the passage in a retrograde direction via a second access closer to the trunk.



Native Upper Arm Shunts


In lesions near the anastomosis, retrograde puncture of the upper cephalic vein is performed at a position near the trunk. If the lesion is located more centrally, a puncture site is chosen close to the anastomosis (Figs. 117-1 and 117-2). A double access is often advisable in thromboses of upper arm shunts, whereby the puncture can be made in the thrombosed venous portion and thrombectomy first performed on one segment via retrograde access and then the second segment via antegrade access.




Ipsilateral puncture of the internal jugular vein with retrograde probing has been described as an alternative access to the brachiocephalic vein.4




Technical Aspects


Percutaneous Treatment


Published literature describes a number of approaches to treating clotted native fistulas:



Frequently a combination of methods becomes necessary to finalize a case. All methods have been used with success, and interventional radiologists should be familiar with several of them to achieve best possible results.



Thrombolysis


Thrombolysis is (relatively) infrequently described to treat native fistulas. Rajan et al.5 described their experience in 25 fistulas with 30 episodes of occlusion, including 19 forearm radiocephalic fistulas in 18 patients and 6 upper arm brachiocephalic fistulas in 6 patients. Lytic therapy with urokinase or recombinant tissue plasminogen activator (rtPA) was administered as a bolus into the fistula in 24 cases, with the exception of one case in which a 16-hour infusion of rtPA was initiated. Clinical success was achieved in 73% of cases (22 of 30). All patients were followed for a maximum of 66 months (mean 12 months). Primary patency rates were 36% at 3 months and 24% at 1 year. The assisted primary patency rate was 40% at 3 months and 32% at 6 months. The secondary patency rate stabilized at 3 months was 44%. Patency rates after clot removal were not significantly different between upper and lower arm fistulas.


Schon and Mishler6

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Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on Percutaneous Management of Thrombosis in Native Hemodialysis Shunts
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