Departments of Cardiovascular Radiology, Clinique St-Gatien, Tours, Clinique St-Hilaire, Rouen, Hôpital Européen Georges Pompidou, Paris, France
Correspondence and offprint requests to: Luc Turmel-Rodrigues, Departments of Cardiovascular Radiology, Clinique St-Gatien, Tours, Clinique St-Hilaire, Rouen, Hôpital Européen Georges Pompidou, Paris, France. Email: luc.turmel{at}wanadoo.fr
Keywords: percutaneous transluminal angioplasty; stents and prostheses; thrombectomy; vascular access thrombosis
All published series concerning percutaneous treatment of thrombosed native fistulae and prosthetic grafts report that an underlying tight stenosis is unmasked in the vast majority of cases, which means that preventive treatment of such stenoses would have avoided acute thrombosis. Vascular access stenosis and thrombosis can nowadays be routinely treated by interventional radiology techniques, which includes dilatation of stenoses with or without stent placement and many declotting techniques [1].
Vascular access dilatation and stent placement
Dilatation or percutaneous transluminal angioplasty is performed with catheters carrying inflatable balloons of different sizes (316 mm in dialysis access) and lengths (28 cm). Special balloons with rated burst pressures of 20 atm are often necessary to abolish the waist of hard fibrotic venous stenoses. Expensive balloons carrying microblades (cutting balloons) can also be used.
Stents are extremely useful in selected indications but all reports show that they are not the panacea and that their patency is limited because stenosis recurs, either in-stent or at its extremities. Increasing in-stent neo-intimal hyperplasia can make it impossible to redilate in the long term. Future access sites must therefore be anticipated before placing stents. For example a stent placed in the subclavian vein should not overlap the ostium of a patent internal jugular vein. This vein is essential for placing a future central catheter [2]. Similarly, a stent must not be placed in either brachiocephalic vein if the stent would overlap the superior vena cava and potentially cause extrinsic stenosis on the contralateral brachiocephalic trunk. The consequence would be a handicapping arm oedema when a new vascular access is placed on the contralateral limb.
There is general agreement concerning the value of stent placement for control of acute ruptures complicating dilatation when the usual technique of prolonged balloon inflation fails [3]. However, the main indication for stent placement is elastic recoil: in some instances the waisting of the stenosis is completely abolished by the inflated balloon but the venous wall collapses and the stenosis recurs as soon as the balloon is deflated and removed. This is frequently the case in central veins so that some teams think that primary stent placement is warranted in this location [4].
The disappointing results to date for covered stents lead to recommending them only for rupture control but trials with new prototypes are in progress [5].
Declotting of thrombosed accesses
This can be performed by pharmacological or mechanical means, or a combination of both. Pharmacological methods use local infusions of thrombolytics (urokinase, rTPA). Mechanical methods include manual catheter-directed thromboaspiration [6], high pressure fluid injection through catheters with multiple side holes (pulse-spray) [7], detachment and deliberate pulmonary embolization of the clots with Fogarty-type catheters [8], thrombectomy devices working on the Venturi effect or on the creation of a vortex [9] and mechanical devices with a direct mechanical action on the vessel wall [10].
Peripheral access stenosis and/or thrombosis: endovascular or surgical intervention?
Although there is general agreement on primary endovascular treatment of central vein stenoses, it is less clear whether peripheral stenoses or subsequent thrombosis should be treated by conventional surgery or by the endovascular techniques initially described and performed by interventional radiologists. An additional level of confusion is that nowadays many surgeons and some nephrologists do perform endovascular techniques.
The patients and their referring nephrologists might stipulate five requirements for treatment: minimal invasiveness, safety, effectiveness, durability and preservation of the venous reserve. Unfortunately analysis of the available literature shows that, in the vast majority of cases, neither surgery nor interventional radiology provides a positive response to these five requirements. In addition, the value of the patient's venous reserve is linked to his life expectancy: it is essential to preserve healthy veins and future access sites in young patients whereas this strategic point is less crucial in the elderly.
How to approach problems with prosthetic grafts?
It has been fairly clearly demonstrated that conventional surgery might be slightly more effective and durable than the endovascular approach for prosthetic grafts but surgery is more invasive, with consumption of normal veins at the venous anastomosis [11]. Prosthetic grafts and their complications should be marginal in Europe. However, this is not always the case since for example a proportion of 30% of grafts are reported in the Netherlands, which is less amazing since the recent publication of a Dutch surgical article promoting placement of forearm grafts even when an elbow autologous fistula is feasible [12].
However, this slight superiority of conventional surgery over endovascular techniques for prosthetic grafts is not so clear as many surgeons now dilate stenoses.
Respective success rates in native a-v fistulae with isolated stenosis
The respective roles for surgery and endovascular techniques might be easier to determine for native fistulae, which should represent the vast majority of haemodialysis accesses throughout the world. Although there is little surgical literature available, the reported success and primary patency rates after surgical revision of isolated stenosis of native radiocephalic fistulae located in the lower forearm are clearly better than those achieved by interventional radiology [1,13]. A Finnish trial even demonstrated that anastomotic stenoses at the wrist were associated with the poorest results of dilatation [14]. There is therefore enough information to claim that such stenoses should be treated surgically by creation of a new anastomosis. However, as long as a randomized multicentre trial has not confirmed the superiority of surgery in this location, it is likely that we will still see dilatation balloons or inappropriately placed stents in veins of the lower forearm.
Delayed a-v fistula maturation associated with vessel stenosis
In contrast, although again no randomized trial is available, interventional radiology has never been proven to be less effective or durable than conventional surgery for any other stenosis located in any type of native fistula [1,15]. Minimal invasiveness and better venous preservation are therefore the two arguments that support a primary endovascular approach.
In addition, it can even be claimed that interventional radiology is more effective than surgery in two instances, i.e. immature fistulae and acutely thrombosed fistulae when the underlying stenosis is not located in the lower forearm.
Delayed maturation of fistulae due to long or multiple stenoses located either on the vein or on the artery can be treated only by dilatation, with 40% primary and 80% secondary patency rates at 1 year [16]. Conventional surgery is only able in such cases to interpose prosthetic grafts or to lose decimetres of forearm veins by creation of an elbow anastomosis.
For thrombosed fistulae, many recent articles have reported excellent success rates, ranging from 76 to 94% [1,17], whereas there are very few surgical articles, with success rates below 30% when the stenosis is not located at the wrist. The results of surgery are historically so poor that two American surgical teams recently wrote that they did not even try to declot a thrombosed autologous fistula [18,19].
Importance of expertise and excellent imaging
However, the excellent results of the endovascular approach have been achieved by dedicated interventional radiologists working in angiography suites, not by physicians working with basic operating room fluoroscopic C-arms. Unlike prosthetic grafts, the vast majority of autologous fistulae must be evaluated from the feeding artery to the hand, and from the anastomosis to the superior vena cava. A concomitant precarious arterial supply to the hand or a central vein stenosis modifies strategy for stenosis treatment and there is therefore no appropriate treatment without excellent imaging. Such morphological studies can be performed only in modern angiography suites, and the patient directly referred to a dedicated radiologist has the benefit of having the fistula imaged and treated optimally in a single stage.
It is disturbing to see how recent articles published in surgical journals either ignore or express scornful opinions about the value of interventional radiology in dysfunctional and thrombosed fistulae [20]. In current practice, such surgeons can survive only with the unconscious or deliberate complicity of nephrologists responsible for the dialysed patients, which means that nephrologists are the key to any change in practice linked to local surgical dictatorships.
Conclusion
Apart from isolated stenoses in wrist fistulas, there is no argument against the fact that stenosis and thrombosis of any type of vascular access should first be treated percutaneously, given the advantages of minimal invasiveness and better preservation of venous capital. In addition, interventional radiology can save fistulae, which are unsalvageable by surgery. However, surgery must be reconsidered in cases of rapid and repeated recurrence of stenoses.
Protocols using the best of monitoring, imaging and interventional radiology and surgery will provide the best results as long as the patient, and not the pride or the financial interest of practitioners, remains the focus of the action.
Acknowledgments
The author thanks Doreen Raine for editing the english.
Conflict of interest statement. None declared.
References