Commentary: Treating Subacute Thrombus in Peripheral Arterial Disease

Intravascular thrombus is associated with prolonged procedures, more contrast use, greater radiation exposure, and a higher incidence of adverse events, including distal embolization. Thrombotic occlusions can be acute (<24 hours), subacute (>24 hours to 4 weeks), or chronic (>1 month). Acute limb ischemia (ALI) is generally the presenting symptom of an acute thrombotic event in a vessel with no supporting collaterals and is associated with high rates of amputation and death. In ALI, the immediate goal of treatment is to rapidly establish normal flow into the vessel with minimal adverse events to save the limb and reduce vascular-related death. Generally, the thrombus is less organized and has formed in situ; less frequently, it may be organized and has embolized from a proximal site. Pharmacomechanical interventions or surgical embolectomy performed emergently are important to restore flow and maintain organ viability. On the other hand, subacute ischemia is relatively less emergent, but if rest limb pain is present and the limb is marginally threatened (Rutherford category IIA), treatment becomes relatively urgent. As the thrombus ages (generally beyond 5 days), it becomes more organized with an ingrowth of smooth muscle cells, connective tissue, and capillary vessels. The more organized the thrombus, the harder it is to dissolve or remove. Since the subacute clinical presentation is less of an emergency, catheter-directed lysis becomes a viable option for treatment. Although effective, this strategy requires a higher dose of a lytic drug and multiple procedures within the same hospital stay, leading to increased bleeding and major adverse events, higher costs, and prolonged hospitalization. Another strategy in treating subacute thrombus is mechanical, with laser ablation or cutting/aspiration using newer rotational atherectomy devices [JetStream (Boston Scientific, Natick, MA, USA) or Rotarex (Straub Medical AG, Wangs Switzerland)]. This is likely to be partially effective, but additional treatments are generally required. Also, the impact of significant residual thrombus on procedure success, recurrent occlusions, and long-term results is unknown. The search for an ideal strategy for treating these subacute thrombi has led investigators to combine mechanical tools and pharmacological therapies to achieve optimal results with a low complication rate. The ultimate goal of reducing thrombus burden and enhancing lysis at a smaller dose is to achieve higher procedure success, reduce major adverse events, lessen the need for repeat procedures, shorten hospital stay, and achieve good long-term outcome. Several pharmacomechanical procedures have been adopted in treating subacute thrombi, including lytic infusion into the thrombus via direct contact with ClearWay porous balloon catheter (Atrium Medical Corporation/Maquet Cardiovascular, Hudson, NH, USA), a power pulse spray (P-PS) of lytic drug followed by rheolytic thrombectomy [AngioJet (Boston Scientific)], mechanical vibration and local lytic dispersion followed by aspiration [Trellis (Covidien, Mansfield, MA, USA)], or laser-enhanced fibrinolysis. Variable results were achieved with mostly partial thrombus resolution. Many of these studies, however, have included subacute and chronic thrombotic occlusions and therefore a more resistant thrombus, which could explain the partial response to treatment. Ultrasound-accelerated lysis of acute thrombotic occlusions has been recently reported to be effective in the treatment of submassive and massive pulmonary embolization and deep vein thrombosis. Its application in the treatment of acute and subacute arterial thrombotic occlusions has been limited, although encouraging results were noted in small observational studies. Using low-power, highfrequency acoustic pulses of varying waveforms, lysis is accelerated by increasing the contact of the lytic agent with the plasminogen receptor sites on the thrombus. This 566908 JETXXX10.1177/1526602814566908Journal of Endovascular TherapyShammas research-article2014