Treatment of acute stent thrombosis with local urokinase therapy using catheter-based, drug delivery systems: a case report

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.

Stent thrombosis: historical perspectives and current trends

Coronary stents are now implanted in more than 70% of percutaneous coronary revascularization procedures. Early enthusiasm for improved acute angiographic results and limited restenosis was dampened initially by a high rate of stent thrombosis and later by the increased bleeding complications of aggressive and complex anticoagulation protocols designed to lower the stent thrombosis risk. More recently, routine high-pressure deployment strategies and anti-platelet drug regimens have lowered the incidence of stent thrombosis to approximately 1% without an increased bleeding risk. The timing of stent thrombosis has also changed from a median of 4-5 days to a median of 1 day after the stent procedure. Risk factors in earlier studies included stenting for threatened or abrupt closure, smaller vessels, longer lesions, and possibly left anterior descending artery lesion location. Modern studies have shown a slightly increased risk for multiple stent use, residual dissection, and smaller final lumen. Optimal therapy for stent thrombosis includes emergent revascularization and anti-thrombotic treatment, although the clinical consequences remain dire despite successful reperfusion. The use of platelet glycoprotein IIb/IIIa inhibitors, especially in high-risk situations may further reduce the incidence of stent thrombosis.

Thrombosis and Hemostasis in Cardiology: Review of Pathophysiology and Clinical Practice (Part I)

The adverse consequences of thrombosis are per haps nowhere more evident than in clinical cardiology. Throm bosis and hemostasis are primary issues in the management of patients with atrial fibrillation, prosthetic heart valves, severe left ventricular dysfunction, and coronary artery disease. Clini cal trials have defined a crucial role for anticoagulation with warfarin in patients with atrial fibrillation to reduce the inci dence of stroke. Anticoagulation with warfarin and aspirin in combination offers significant protection from systemic emboli in patients with mechanical prosthetic valves, without a sub stantial increased risk of hemorrhage. The risk of systemic emboli may also be reduced by anticoagulation in patients with severe left ventricular dysfunction. Disturbance of the normal balance of hemostasis is a major factor in the pathophysiology of coronary artery disease. Antiplatelet therapy, antithrombin agents, anticoagulants, and fibrinolytic agents have been used to prevent and treat acute coronary thrombosis and to prevent reocclusion following thrombolysis and interventional therapy. Guidelines are presented for antithrombotic therapy in the prac tice of clinical cardiology.

Local delivery of heparin with balloon angioplasty: results of a prospective randomized trial

PURPOSE

To evaluate the effectiveness of local delivery of heparin via hydrogel-coated balloons in the treatment of vascular stenoses associated with hemodialysis access.

MATERIALS AND METHODS

This was a randomized, prospective trial comparing treatment with hydrogel-coated balloon catheters delivered with heparin coating (n = 33) and without (n = 26). All patients were undergoing hemodialysis, and all stenoses involved the venous anastomosis of a dialysis graft or a native vein. The heparin-treated balloons were soaked in concentrated heparin and delivered in a protected manner to help prevent washout of heparin.

RESULTS

The mean primary patencies were 143 days with heparin treatment and 214 days without heparin (P = .174). The mean assisted primary patencies were 165 days with heparin and 194 days without (P = .315). The mean secondary patencies were 351 days with heparin and 384 without (P = .81).

CONCLUSION

In this population with this technique, the treatment outcome of venous outflow stenosis in patients with dialysis grafts is not improved with local delivery of heparin.

Contemporary stent designs: technical considerations, complications, role of intravascular ultrasound, and anticoagulation therapy

A number of studies have shown the benefits of stent placement over balloon angioplasty for the treatment of focal, native coronary artery, and saphenous vein graft disease. Although the number of stent designs available for clinical use has increased dramatically, the late clinical benefit of stenting over balloon angioplasty has yet to be shown in diffuse disease, complex bifurcation stenoses, or smaller (2.5-mm) vessels, each of which may require unique stent designs and adjunct therapies not currently available or extensively studied. The purposes of this review are to discuss the various stent designs currently available for clinical use, outline the known complications associated with these stents, assess the contribution of intravascular ultrasound, and describe current antiplatelet and antithrombotic therapy used after stent use.

Coronary angioplasty and intracoronary thrombolysis are of limited efficacy in resolving early intracoronary stent thrombosis

OBJECTIVES

This study sought to evaluate treatment of early intracoronary stent thrombosis.

BACKGROUND

Although refinements in intracoronary stent implantation technique and pharmacologic treatment have reduced the frequency of early stent thrombosis, stent thrombosis remains a feared complication of this procedure. Optimal treatment for stent thrombosis is still undefined.

METHODS

Twenty-nine patients (44 stents) with early (< or = 30 days) coronary stent thrombosis over a 5-year period at our institution were identified. Treatment and outcome of stent thrombosis were analyzed.

RESULTS

Mean (+/- SD) time from implantation to stent thrombosis was 6.1 +/- 5 days. Twenty-three patients were treated with catheter-based therapies (angioplasty alone in 14, angioplasty and intracoronary urokinase in 7, intracoronary urokinase alone in 2). Flow was restored without residual thrombus in 11 (48%) of the catheter-treated patients (6 of 14 with angioplasty alone, 4 of 7 with angioplasty and urokinase, 1 with urokinase alone). Of the 23 patients, 2 died despite restoration of anterograde flow, and 9 were referred for emergent or urgent bypass surgery because of residual thrombus and refractory angina despite restoration of blood flow. Of the remaining six patients, five were treated medically and one with coronary bypass surgery; three died. Acute myocardial infarction evolved in 26 patients (90%), including 20 (87%) of the 23 catheter-treated patients.

CONCLUSIONS

Stent thrombosis is associated with severe adverse outcomes. Although catheter-based therapies are effective in restoring patency in a majority of patients, patients are referred frequently for coronary bypass surgery because of residual thrombus and refractory angina. These findings suggest that alternative or adjunctive therapies for stent thrombosis are needed.