Current Options in the Diagnosis and Management of Acute Limb Ischemia

Karthikeshwar Kasirajan, MD, Kenneth Ouriel, MD

Disclosures

Prog Cardiovasc Nurs. 2002;17(1) 

In This Article

Percutaneous Mechanical Thrombectomy (PMT) Devices

There exist a number of percutaneously delivered devices that can remove thrombus from peripheral arteries using a rapid stream of fluid and hydrodynamic forces to extract the thrombotic material from the lumen.[12,13,14,15] These devices include the Angiojet rheolytic catheter (Possis Medical, Minneapolis, MN), the Hydrolyser (Cordis, Warren, NJ) and the Oasis device (Boston Scientific, Boston, MA). The devices differ in the method of fluid delivery; while the Possis device uses a dedicated fluid delivery machine to achieve rapid flow rates, the latter two devices employ a standard angiographic injector. Currently, the Angiojet is the only PMT device that is approved by the Food and Drug Administration (FDA) for use in the peripheral arterial circulation.

The available devices have a number of limitations. There always exists the potential to induce distal embolization as the device is passed through the thrombus. The efficacy of the device is limited by the diameter of the cylindrical "core" of thrombus that can be extracted with each pass of the catheter; a property that is dependent on the size of the device. This limitation, however, must be balanced by the convenience of placing the device through a relatively small-bore sheath, as well as the increased safety associated with use of a smaller device in the tibial vessels. Another limitation of the currently available devices is the amount of red blood cell damage that can occur. Hemolysis with hemoglobinemia and hemoglobinuria may occur, especially with repeated passes of the device. Lastly, fluid overload can develop if one is not careful to monitor the amount of irrigation instilled intravascularly during use. Despite these theoreticl limitations, fluid overload and hemolysis have not proved to be a problem in preliminary clinical trials.[12,13,14,15]

The ability of PMT devices to rapidly restore arterial perfusion is an attractive advantage over pharmacologic thrombolysis alone. In patients with very significant ischemia that precludes the obligatory delay associated with pharmacologic thrombolysis, the PMT devices may rapidly clear a channel through the occluded segment. Partial reperfusion of the extremity may provide enough improvement in ischemia to allow complete removal of thrombus, with thrombolytic infusions thereafter. Initial thrombus debulking may also significantly reduce the dose and duration of thrombolytic agents, thereby decreasing the risk of hemorrhagic complications associated with pharmacologic thrombolysis.[6,12,13,15] Also, the devices may be employed as sole therapy in patients with contraindications to thrombolytic administration -- for instance, patients who have recently undergone a major surgical procedure.

A variety of "brushes," rotating wires, and PMT devices that simply fragment the thrombus without actually aspirating the fragments have been designed to establish arterial recanalization. This class of device includes the Amplatz Thrombectomy Device (Clot Buster) (Microvena Corporation, White Bear Lake, MN), Arrow-Trerotola PTD (Arrow International, Inc., Reading, PA), Castañeda Brush (Micro Therapeutics, Inc., Aliso Viego, CA), and Cragg Brush (Micro Therapeutics, Inc., Aliso Viego, CA) devices.[16,17,18] While these devices have gained a foothold in the treatment of dialysis access graft occlusion, clinicians have been reticent to use them in the periphery for fear of injuring the vessel wall. Additionally, a potential limitation of this class of device is the problem of distal embolization of macroparticles of thrombus.[19]

Among the PMT devices, the largest clinical experience has been with the Angiojet catheter, and currently this is the only FDA-approved peripheral arterial thrombectomy device.[6,13,14] The thrombectomy system consists of three major components: the catheter, the pump set, and the drive unit. The pump set and the drive unit are responsible for producing a controlled, high-velocity saline jet (350-450 km/hr) that is redirected at the tip of a dual-lumen catheter back into the effluent lumen of the catheter. As shown in Figure 4, the inflow lumen is a low-profile stainless-steel tube that forms a transverse loop at the distal end of the catheter and has multiple 25-50-mm diameter orifices directed retrogradely toward the inflow lumen. Saline solution from the pump drive unit is driven at 50-60 mL/min at 8000-10,000 psi, resulting in a high velocity at the catheter tip. The high velocity of the saline jets produces an area of extremely low pressure (Venturi effect) that is exposed to the intra-arterial lumen only at the catheter tip, referred to as the "gap zone." Thrombus surrounding the catheter tip is fragmented (99.8% less than 100 mm)[20] and rapidly evacuated through the effluent lumen in an isovolumic manner (fluid instilled = fluid and blood removed). Since thrombus removal is not produced by the actual mechanical force of the saline, but by an indirectly created negative pressure zone (2760 mm Hg), luminal endothelial damage is kept to a minimum.

The Angiojet thrombectomy system

Three different types of catheter designs are currently available: the CF105, LF140, "e-train," and, more recently, the "Xpeedior" catheter (Figure 5). The different catheter models were a result of design modification of the catheter tip in an attempt to improve thrombus extraction.

Tip of the Xpeedior thrombectomy catheter, demonstrating the recirculating fluid vortex that results in thrombus extraction

In vitro studies comparing endothelial denudation of the Angiojet and the Fogarty thrombectomy catheter have demonstrated significantly greater mean endothelial loss for Fogarty balloon catheter-treated vessels (58% vs. 88%).[20] Particulate embolization accounted for only 12% of the initial thrombus volume, and 99.83% were smaller than 100 mm.[20] Hemolysis equivalent to that resulting from lysis of 75 mL of blood was seen after a standard pump run, but no elevation in blood urea nitrogen or creatinine was noted.[20] Clinical trials using PMT devices for acute, limb-threatening ischemia are shown in Table 5 .

It appears unlikely that mechanical thrombectomy will completely eliminate the need for pharmacologic thrombolysis or open surgery.[12,13,18,21,22] In all but one clinical report,[14] a significant number of patients required adjunctive thrombolytic therapy for complete thrombus removal. The advantage of mechanical devices, however, lies in their ability to rapidly debulk the thrombus (Figure 6A and 6B), significantly reducing the duration of ischemia and probably increasing the exposure of the residual thrombus and distal vessels to pharmacologic thrombolytic agents. The reduced dose and time needed to achieve complete thrombolysis may result in considerable cost savings and reduced bleeding complications.[6] In patients with a contraindication to pharmacologic thrombolysis and at high risk for open surgery, PMT may represent the best therapeutic option. Braithwaite et al.[23] managed 15 patients with ALI with anticoagulation alone, due to infirmity or surgical and/or thrombolytic contraindications, and obtained dismal 30-day limb salvage and mortality rates of 33% and 60%, respectively.

Diagnostic angiogram demonstrating total occlusion of the left limb of an aorto-bifemoral graft.

Complete thrombus removal following percutaneous mechanical thrombectomy with the Xpeedior catheter.

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