The purpose of percutaneous mechanical thrombectomy devices is to soften, fragment, and extract occlusive thrombus. They may be used without adjunctive thrombolytic therapy, although many patients require both modalities for effective treatment. The therapies are complementary; the device is capable of reducing or eliminating the thrombus burden as well as modifying the clot to expose more surface area to the lytic agent. There are a variety of technologies to accomplish this. Suction, ultrasound, fluid, and mechanical methods have been developed (Table 1). Suction catheters represent the first generation of these devices and are used to simply evacuate the clot by placing a vacuum at the tip of any large catheter buried within the clot and withdrawing the catheter with the attached thrombus. This procedure is moderately effective for the extraction of short, fresh clot but is generally of little benefit as solo therapy for the treatment of acute ischemia from long or adherent thrombus. TABLE 1 Commonly Used Percutaneous Mechanical Thrombectomy Devices Several degrees of severity of lower extremity ischemia can accompany acute arterial or graft occlusion (Table 2). Patients in categories I and IIa have limbs that are not immediately threatened and should be considered for fibrinolytic therapy. Those in category IIb must be carefully evaluated for the most expeditious method of restoring blood flow. Because lysis of even fresh thrombus often requires infusions of 3 hours or more, many investigators hesitate to attempt percutaneous intraarterial lytic therapy in patients with critical ischemia and deterioration of neuromuscular function because the activation of plasminogen may initially be slow. Additionally, as lysis begins to soften the thrombus, there may be distal embolization. These emboli will respond to continued therapy but will transiently worsen distal perfusion. Therefore, patients with advanced ischemia who have readily accessible, short thrombi may be better served by operative intervention if it can be performed expeditiously. Patients with more extensive thrombosis or involvement of smaller vessels not amenable to mechanical thrombectomy should be considered for percutaneous thrombolytic therapy. Patients in category III, with advanced ischemic changes and absent neurologic function, often require primary amputation. TABLE 2 Clinical Categories of Acute Limb Ischemia
Percutaneous Mechanical Thrombectomy and Fibrinolytic Therapy for Acute Thrombosis of Lower Extremity Arteries and Grafts
Percutaneous Mechanical Thrombectomy Devices
Device
Manufacturer
Mechanism of Clot Disruption
Ekosonic Catheter
EKOS
High-frequency ultrasound
Angiojet Thrombectomy System
Medrad
Rheolytic fluid dynamics
Trellis Infusion Catheter
Bacchus Vascular
Direct physical disruption
Indications for Thrombolytic Therapy
Patient Selection
Description and Prognosis
FINDINGS
DOPPLER SIGNALS
Sensory Loss
Muscle Weakness
Arterial
Venous
I. Viable
Not immediately threatened
None
None
Audible
Audible
II. Threatened
a. Marginal
Salvageable if promptly treated
Minimal (toes) or none
None
(Often) inaudible
Audible
b. Immediate
Salvageable with immediate revascularization
More than toes, associated with rest pain
Mild, moderate
(Usually) inaudible
Audible
III. Irreversible
Major tissue loss or permanent nerve damage is inevitable
Profound, anesthetic
Profound, paralysis (rigor)
Inaudible
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