Cath Lab Digest

Introduction
Peripheral vascular disease (PVD) is thrombogenic.¹ There is a high frequency of elderly patients, diabetics, hyperlipidemics and smokers, conditions associated with hypercoagulation, in patients presenting with PVD. In addition, patients with PVD have a heightened inflammatory state, leading to plaque rupture and subsequent acute and subacute thrombosis and embolization, a mechanism similarly seen in unstable coronary syndromes. Furthermore, patients with PVD have a higher incidence of coexistent coronary disease, myocardial infarction (MI), congestive heart failure and arrhythmias, conditions associated with thrombo-embolism. Finally, occlusions in the peripheral vasculature are likely to contain atherothrombus, usually multilayered acute and/or subacute.

The angiographic presence of thrombus depends on the acuity of the presentation. For instance, fresh thrombus is the hallmark of acute limb ischemia (ALI), present in 100% of these patients. In a recent study, thrombus was present in 16.7% of a PVD population, with 34.4% of these patients having had a recent onset of symptoms.² In contrast, only 3% of patients had angiographic thrombus in an elective population undergoing renal, iliac and femoral percutaneous interventions, with long occlusions excluded.³ Despite these differences, angiography considerably underestimates the true presence of thrombus, particularly in patients with chronic occlusions.

The presence of thrombus in the peripheral vasculature is associated with multiple complications, including amputation, death, higher re-occlusion rates, urgent/ emergent surgical revascularization, embolization, longer procedure times (Figure 1), prolonged hospitalization, and the need for the use of a high level of anticoagulation, generally associated with increase in major bleeding. Effective and safe treatment of thrombus is therefore of critical importance to reduce complications during peripheral percutaneous interventions (PPI).

The approach to treating thrombotic lower arterial disease depends considerably on the acuity of the presentation. Generally patients are divided into three categories:

1. Acute Presentation. This generally occurs within hours of presentation and is associated with rest limb pain and a pulseless foot. The vessel is typically occluded with a thrombus that has occurred on top of mild to severe lesions.

Collaterals are generally minimal or none. The mechanism of acute thrombosis is mostly plaque rupture followed by in-situ thrombosis or migration of a clot distally. In addition, and not infrequently, embolization of a proximal thrombus in patients with MI, arrhythmias and congestive heart failure is seen. Thrombi in these patients tend to be fresh, and an emergent intervention is needed to salvage the limb. This presentation is referred to as acute critical limb ischemia (ALI).

2. Subacute Presentation. This generally occurs within days to a month. The patient typically presents with accelerated limb pain, with minimal activity or at rest. The underlying lesions are usually severe. A high frequency of total occlusions is seen. Typically patients have collaterals, but not enough to sustain adequate lower extremity circulation at rest or with minimal activity. In subacute presentations, there is a high likelihood that a recent thrombus is present, probably organized, and likely overlying additional subacute and chronic thrombus. The presentation of these patients is analogous to unstable coronary syndromes. Patients typically have limb pain with minimal activity [Rutherford-Baker classification (R-B) III], or at rest such as in critical chronic limb ischemia (CLI).

3. Chronic Presentation. This generally occurs within several months to years. The presentation is typically moderate to severe claudication (R-B II and III). In this population, underlying chronic occlusions can occur in about a third of patients. Collaterals are well-developed but remain suboptimal to keep the patient symptom-free. The presence of angiographic thrombus in this patient population is low, but it is our experience that organized thrombus is likely to be present in the majority of chronic occlusions. These patients are analogous to stable angina patients.

As noted, the clinical presentation of the patient is a substantial factor that influences lower extremity thrombus treatment and will affect the technique and anticoagulant of choice periprocedurally. The anticoagulant should be able to prevent further platelet and thrombin activation, reduce macro/micro thrombus downstream, be very effective in penetrating and dissolving existing thrombus, have lower reocclusion rates and be associated with low bleeding complications. Techniques utilized need to effectively restore flow, minimize procedure length, dissolve thrombus in association with the anticoagulant, reduce embolization downstream and have favorable long-term results.

Taking all of the above factors in consideration, we suggest the following algorithms for the treatment of patients with thrombotic lesions. We understand that more research is needed to validate these recommendations, which are based on the best currently available data.