Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3609_Библиотеки_им_академика_М_И_Перельмана

Plain balloon angioplasty is commonly the initial method employed to address stenotic lesions, which are often due to intimal hyperplasia. These venous stenoses can usually be resolved with pressures up to 20 atmospheres, though very high pressure, non-compliant balloons with burst pressures up to 40 atmospheres are also available to treat particularly recalcitrant lesions [5]. PTA of venous outow and juxta­anastomotic stenosis have 1-year primary patency rates rang­ing from 28% to 72% and secondary patency rates at 1year between 68% and 96%, with optimal results achieved when using 4–6mm balloons [8]. However, these high pressures can lead to further intimal hyperplasia due to trauma to the vein, with 15% of patient experiencing rupture of the weak venous wall [8]. The risks of using high-pressure dilation has prompted some surgeons to use a cutting balloon prior to dilation to allow for the use of lower pressures which range from 6 to 8.4 atmospheres [9, 10]. Two randomized clinical

Even in the absence of focal stenoses, some vascular access sites fail to mature, which can be due to overall small size of the venous outow or inadequate vein size. Balloon­assisted maturation (BAM) has been described, which involves serial dilation of the venous outow using relatively low pressures (8–12 atmospheres), with each dilation lasting <15s. BAM is performed multiple times with an average of 2 weeks between each procedure [16, 17]. Early studies reported an increase in volume ow rates in half (54.7%) of patients receiving BAM [16], with a shorter duration to mat­uration in patients receiving BAM (119days vs. 146days in those not receiving BAM); however, this was not signicant (p= 0.73) [17]. More recent studies include a randomized clinical trial which showed shorter maturation time in the BAM group compared to the non-BAM group (3.7weeks vs.

Stenosis in the vascular access circuit can lead to the devel­opment of thrombus in the circuit and complete cessation of ow. Endovascular treatment can be offered to patients with either an AVF or AVG; however, if the vascular access was created within the past month, then endovascular manage­ment can lead to disruption of the anastomoses [6]. It is also important to note that delayed clot removal of more than 2–3days in an AVF is associated with a higher risk of failure, while an AVG thrombectomy can still be successfully per­formed up to 2weeks after thrombosis [6]. One hypothesized mechanism of this observation is that thrombus will adhere more to a native vessel wall than to a prosthetic graft. Thrombolysis and mechanical thrombectomy are the two main types of endovascular treatment for thrombosed vascu­lar access circuits.

Thrombolysis can be performed using several thrombo­lytic agents, including urokinase, streptokinase, or tissue plasminogen activator (tPA), with technical success of thrombolysis alone ranging between 38% and 80%. As such, thrombolysis is usually combined with mechanical throm­bectomy [6]. Several thrombolysis techniques have been described, including “Lyse-and-wait”, pharmacomechanical thrombolysis (PMT), and pulse-spray thrombolysis. The “Lyse-and-wait” technique involves injecting a thrombolytic agent into the thrombus with manual compression of the inow and outow vessels of the vascular access circuit. After a certain wait time to allow the thrombolytic agent time to activate within the thrombus, an angiogram is performed to assess for thrombus resolution [20]. The “wait” time var­ies between different studies, though the average time is usu­ally between 10 and 15 min, since the half-life for both urokinase and tPA are similar and range between 7 and 20min [21]. One study assessed an extended wait time for tPA inltration that averaged 18.6h and ranged between 2 and 40h [22]. This time-extended method had an 82% pri­mary patency rate at 12months and 63% at 24months; how­ever, this method was not compared to the traditional wait times so it is not known if this extended wait time provides any benet over shorter wait times [22]. Another technique is PMT, which involves injecting a lytic agent into the throm­bus and then performing either balloon maceration of the

There are several devices for mechanical thrombectomy, which can be divided into two broad categories: (1) direct wall contact devices and (2) hydrodynamic rheolytic devices that do not have contact with the vessel wall [6]. Direct wall contact devices include the Fogarty thru-lumen embolec­tomy catheter (i.e., “over-the-wire balloon”) (Edwards Lifesciences) and the Cleaner XT Rotational Thrombectomy System (Argon Medical Devices, Plano, TX), which has a rotating sinusoidal wire that macerates the thrombus within the vessel [6]. The use of the Fogarty balloon along with thrombolysis had a median of 434days of primary patency [26]. This lysis-assisted balloon (LAB) thrombectomy tech­nique was also found to be relatively safe, with one study reporting a 6.6% complication rate [26]. Most of these com­plications were minor, including prolonged bleeding from the puncture site, venous rupture successfully treated with balloon ination, and arterial embolization successfully treated with catheter aspiration [26]. In one study, the Cleaner XT device had an 88% success rate with a 65% primary patency rate and a 76% secondary patency rate both at 1month [27]. One of the complications reported is the risk of AVF rupture which occurred in 3 out of 17 patients; however, none of the ruptures led to loss of the vascular access circuit [27]. Hydrodynamic rheolytic devices create a vortex by uti­lizing high-speed uid jets to break the clot and create a negative pressure gradient which, along with aspiration, removes the thrombus fragments, all without any contact with the vessel wall [6]. There are several devices on the market with the most widely used and studied being the AngioJet (Boston Scientic, Marlborough, MA) and the Indigo System (Penumbra, Alameda, CA). In a systematic review of articles assessing the efcacy of the AngioJet device in the treatment of vascular access circuit thrombosis, the adjusted mean primary patency rates were 64.6% and

30.5% at 1 and 12months, respectively [28]. The complica­tion rate was 15.1% and most were bleeding and hematomas (13.5%), vein ruptures (7.9%) which were treated with stent grafts, and arterial emboli (7.1%) none of which resulted in limb loss [28]. The rest of the complications were considered minor as they did not result in any further intervention and included bleeding and hematoma, fever, transient arrhythmia not requiring treatment, contrast extravasation, and device failure [28]. There were 7 recorded deaths, most of which were due to cardiac causes such as arrhythmias, myocardial infarction, and cardiogenic shock; however, these could not be attributed to the use of the AngioJet device [28]. Two studies reviewing the Indigo System found similar results.