Mechanical Thrombectomy Devices Supplement Thrombolysis

Managing thrombosis comprises a critical part of vascular patient care, because the development of thromboses poses considerable risk throughout the body, frequently precipitating stroke, myocardial infarction, compromised circulation and ischemia. Sites at particular risk for thromboses formation include dialysis access grafts, ischemic lower extremities with native artery or bypass occlusions, iliofemoral deep veins, cerebral arteries and coronary bypass grafts, which are prone restenose and to seed distal thromboemboli.
Percutaneous revascularization of thrombus-containing lesions has an increased incidence of adverse events such as abrupt vessel closure, periprocedural myocardial infarction and death. Various pharmacologic agents and mechanical approaches have demonstrated modest angiographic success with significant periprocedural complications.
The pharmacological treatment of thrombosis has advanced in recent years with the growing familiarity with tissue plasminogen activators (rt-PAs), the market withdrawal and return of urokinase, and the advent of newer agents such as tenecteplase and plasmin-based products. Despite these developments, many patients remain refractory to pharmacotherapy. Moreover, the collective costs of such therapy are daunting among those in whom thrombosis can be treated in-hospital by large doses of lytic agents.
In those patients non-responsive to pharmacotherapy, the application of mechanical trombectomy devices (MTDs) is expanding to encompass a greater range of thrombotic sites. These devices fall into two broad categories, those that fragment the thrombus, with or without clot removal and those that contact the vessel wall.
The advantages of MTDs can include faster reperfusion of ischemic limbs, potentially shorter hospital stays than those required for lytic drug administration alone, and lower rates of rethrombosis. MTD therapy also may provide comparative advantages of safety by leading to fewer bleeding complications, because they can reduce lytic drug doses, or eliminate them altogether. This theoretical advantage, however, must be balanced against device risks such as distal embolization, hemolysis, and vessel wall damage, the likelihood of which varies with each specific device and application.
Mechanical thrombolytic devices have become the mainstay of percutaneous treatment of clotted dialysis grafts. Properly used, they are faster, safer and equally or more effective than chemical lysis. This was one of the main findings presented at the recent conference of the Cardiovascular and Interventional Radiological Society of Europe (CIRSE 2003).
Surgical literature indicates that removing wall-adherent material (clot and pseudointima) is not only desirable but also essential for improved patency of these grafts. Currently, only two wall-contact devices are approved by the FDA for de-clotting synthetic dialysis grafts: the Arrow-Trerotola percutaneous thrombolytic device from Arrow International, Reading, Penna. and the Akonya Eliminator from IDev Technologies, Houston.
In a broader category, the AngioJet (Possis Medical, Inc., Minneapolis) is the only thrombectomy system currently approved for peripheral arterial applications; although many other MTDs have been used off-label for this purpose. The AngioJet is a dual lumen catheter designed to rapidly remove blood clots with minimal vascular trauma. In April 2000, March 1999 and December 1996, Possis received FDA clearances to commence United States marketing of the AngioJet System, for removal of blood clots in leg arteries, native coronary arteries and coronary bypass grafts and access grafts used by patients on kidney dialysis, respectively. The AngioJet System is typically used in conjunction with other medical devices, such as angioplasty balloons and stents (both bare metal and drug eluting), and drugs, such as thrombolytics and platelet inhibitors. Possis also markets the XMI, XVG, Xpeedior and AVX catheters. Each of these catheters features the company's proprietary Cross-Stream Technology.
When compared with urokinase in the randomized VeGAS 2 Trial, AngioJet therapy yields greater angiographic success with a lower incidence of 30-day major adverse events.
The Trellis, manufactured by Bacchus Vascular, Inc., Santa Clara, Calif., is a novel drug infusion device designed for isolated thrombolysis. A thrombus is isolated between two occlusion balloons while the thrombolytic is mechanically dispersed with an oscillating wire and then aspirated. Theoretically, isolated thrombolysis enables single-setting thrombolysis by delivering a high concentration of thrombolytic agent while preventing systemic dispersion. Adjunctive procedures may be performed in the same single setting. Data from a voluntary company registry for isolated thrombolysis have indicated lower hospital costs due to reduced ICU stay and lytic dosing, and no reported bleeding complications. Bacchus reports that a future registry is planned. The Trellis is approved for use in the peripheral vasculature.