Thrombolysis in acute lower limb ischaemia

Increasing injection frequency enhances the survival of injected bone marrow derived mesenchymal stem cells in a critical limb ischemia animal model

Critical limb ischemia (CLI) is one of the most severe forms of peripheral artery diseases, but current treatment strategies do not guarantee complete recovery of vascular blood flow or reduce the risk of mortality. Recently, human bone marrow derived mesenchymal stem cells (MSCs) have been reported to have a paracrine influence on angiogenesis in several ischemic diseases. However, little evidence is available regarding optimal cell doses and injection frequencies. Thus, the authors undertook this study to investigate the effects of cell dose and injection frequency on cell survival and paracrine effects. MSCs were injected at 10⁶ or 10⁵ per injection (high and low doses) either once (single injection) or once in two consecutive weeks (double injection) into ischemic legs. Mice were sacrificed 4 weeks after first injection. Angiogenic effects were confirmed in vitro and in vivo, and M2 macrophage infiltration into ischemic tissues and rates of limb salvage were documented. MSCs were found to induce angiogenesis through a paracrine effect in vitro, and were found to survive in ischemic muscle for up to 4 weeks dependent on cell dose and injection frequency. In addition, double high dose and low dose of MSC injections increased vessel formation, and decreased fibrosis volumes and apoptotic cell numbers, whereas a single high dose did not. Our results showed MSCs protect against ischemic injury in a paracrine manner, and suggest that increasing injection frequency is more important than MSC dosage for the treatment CLI.

Consultations on Patients with Venous or Arterial Diseases

Advances in vascular biology and drug development, as well as improved interventional techniques, are yielding multiple new treatments for patients with venous and/or arterial thrombosis. Hematologists who are providing consultations for these patients often participate in a multidisciplinary approach to provide optimal care. New anticoagulants, simplified and validated tests for detecting vascular disease, and improved interventional procedures can all reduce the morbidity and mortality that result from venous and arterial thrombosis. In this chapter, different aspects of the diagnosis and treatment of these disorders are addressed by a hematologist, an expert in vascular medicine, and a vascular surgeon.

The key to the prevention and treatment of venous and arterial thrombosis is anticoagulant and antiplatelet therapy. In Section I, Dr. Charles Francis, a hematologist with expertise in thrombosis and hemostasis, describes the clinical trials that have resulted in the approval of newer anticoagulants such as fondaparinux and the thrombin- specific inhibitors. He also reviews the clinical trials that have shown the efficacy of the new oral anticoagulant ximelagatran. Although currently under study primarily for the prevention and treatment of venous thrombosis, these anticoagulants are likely to undergo evaluation for use in arterial thrombosis.

Peripheral arterial disease (PAD), which affects as many as 12% of individuals over the age of 65 years, provides a diagnostic and therapeutic challenge to physicians across multiple subspecialties. Dr. William Hiatt, a specialist in vascular medicine, discusses in Section II the epidemiology and manifestations of PAD, the best ways in which to diagnose this disorder and determine its severity, and the most appropriate pharmacologic treatment.

In Section III, Dr. Mark Jackson, a vascular surgeon, describes interventional procedures that have been developed or are under development to treat arterial thrombosis. He also reviews the status of inferior vena caval filters that are retrievable.

Basic arterial techniques for peripheral arterial thrombolysis

This article is an overview of the techniques of percutaneous intervention for recanalizing acute or subacute occluded arteries. The indications and results for specific thrombolytics and interventions are discussed in subsequent articles.

Thrombolytic therapy with use of alteplase (rt-PA) in peripheral arterial occlusive disease: review of the clinical literature. The Advisory Panel

PURPOSE

The clinical literature describing the use of alteplase in the treatment of peripheral arterial occlusive (PAO) disease is reviewed.

MATERIALS AND METHODS

The literature database was acquired by a MEDLINE search using the Boolean keyword string: tissue plasminogen activator and/or rt-PA and peripheral not animal. A review was performed to identify the dose range of alteplase, technique of infusion, use of anticoagulation, clinical success rates, and risk of complications.

RESULTS

Forty-six clinical studies were identified. There are few prospective, randomized clinical trials and a lack of standardized protocols and endpoints. Use of catheter-directed infusions of recombinant tissue plasminogen activator (rt-PA) may be beneficial versus surgery in the initial management of acute limb ischemia (< 14 days) and in reducing the magnitude of subsequent surgical or percutaneous revascularization. For patients with chronic limb ischemia (> 14 days), irreversible acute limb ischemia, or advanced diabetic arteriopathy, catheter-directed infusion of rt-PA or other plasminogen activators may be unsuitable. The risk of adverse bleeding appears related to the overall dose and duration of infusion. These risks appear similar to those of urokinase. The role of heparin in increasing adverse bleeding during rt-PA therapy is unclear.

CONCLUSIONS

There is no generally accepted dose or technique for administering catheter-directed thrombolysis using alteplase; however, several studies have demonstrated its clinical safety and efficacy. Formal studies will be required to determine the optimal dose, technique of infusion, the role of anticoagulation, and complication rates when alteplase is used for PAO disease.

Exposure to thrombus diminishes endothelial derived relaxation in the rabbit carotid artery

PURPOSE

Thrombus is believed to be deleterious to intimal function. However, few studies have directly examined this effect. This study examines the effect of thrombus on endothelial-dependent and -independent vasorelaxation in the rabbit carotid artery.

METHODS

Twelve male New Zealand white rabbits (3.5-4.5 kg) were divided into two groups of six. Thrombosis was induced in group I by segmental right carotid artery ligation. Group II underwent segmental right carotid ligation immediately followed by removal of thrombus with normal saline flush through an arteriotomy. The left carotid arteries were exposed in both groups and served as internal controls. After 4 h, left and right carotid arteries were harvested, sectioned into 6-mm rings, and mounted on isometric force transducers in a physiologic bath. Thrombus was removed from the arteries in group I during the ring preparation process. Neither group I nor group II had thrombus in contact with endothelium during ex vivo testing. The arterial rings were constricted with norepinephrine (1 x 10(-4) M). Endothelium-dependent and -independent vasorelaxation to acetylcholine (Ach) and s-nitrosoacetylpenicillamine, respectively, were measured in a dose-response manner. Results were expressed as a percentage of vasorelaxation. Statistical analysis was performed using an analysis of variance.

RESULTS

Endothelial-dependent vasorelaxation, which tests for endothelial cell function, was decreased in the thrombus and endothelial ischemia group (I) compared to control as noted by vasorelaxations of 22% vs 34% at 1 x 10(-4) molar concentration Ach, and 33% vs 48% at 1 x 10(-3) molar concentration Ach, respectively (P = 0.05). By comparison, there was no difference in the endothelial-dependent vasorelaxation of the endothelial ischemia group (II) versus control. Endothelial-independent vasorelaxation, which tests for smooth muscle function, was not affected by either the thrombus and endothelial ischemia group (I) or the endothelial ischemia group (II) compared to the control group. The controls in group I and group II were slightly different. When this difference was removed, the resulting comparison of treatments in group I and group II approached significance at molar concentrations of 1 x 10(-4), 1 x 10(-5), and 1 x 10(-6) (P = 0.07, 0.06, 0.06).

CONCLUSIONS

The presence of thrombus within the rabbit carotid artery for a period of 4 h decreases endothelial-dependent relaxation. Four hours of endothelial ischemia without thrombus did not change endothelial-dependent vasorelaxation. Neither thrombus nor ischemia alone had any effect on the endothelium-independent vasorelaxation. We conclude that thrombus is deleterious to endothelial function independent of smooth muscle function in the acute setting as measured by endothelial-dependent vasorelaxation.

Prospective randomised comparative study of pulse spray and conventional local thrombolysis

OBJECTIVES

To compare the time required to achieve lysis with the pulse spray technique and the conventional slow continuous infusion technique.

DESIGN

Prospective randomised open Study.

METHODS

Eighteen patients suitable for intra-arterial thrombolytic therapy with conventional and pulse spray technique were randomised 1:1 to receive either pulse spray thrombolysis with 0.33 mg/ml rt-PA injected as a bolus of 0.2 ml or conventional thrombolysis with 0.05 mg/ml rt-PA infused at a rate of 10 ml/h.

RESULTS

The age, duration of symptoms, length of occlusion and prethrombolysis ankle brachial pressure index were comparable in the two groups. The median duration of thrombolytic therapy in the pulse spray group was 195 min (range 90-1260) compared to 1390 min (range 300-2400) in the Conventional group. The difference between the two groups was significant, p < 0.002 (Mann-Whitney test).

CONCLUSIONS

Significantly shorter time is required to achieve local thrombolysis with pulse spray compared to the conventional infusion method.

The role of thrombolysis in the management of thromboembolic disorders: a four-year review

OBJECTIVE

To examine the role of thrombolysis alone, or in conjunction with surgery and angioplasty, in the treatment of thromboembolic disorders.

DESIGN

A retrospective review of 70 patients, who received thrombolysis on 73 occasions between 1990 and 1993.

PATIENTS AND METHODS

Four groups were defined: (1) thrombolysis alone (40%); (2) thrombolysis followed by angioplasty (23%); (3) thrombolysis followed by surgery (13%) and (4) thrombolysis after failed angioplasty (24%).

RESULTS

Twenty-eight patients (40%) received thrombolysis alone of which 13 were successful. In 25 cases (36%) thrombolysis was initially successful in that it permitted further angioplasty or surgical reconstruction. This adjunctive treatment was successful in 16 cases. Overall, when used as a first-line treatment, thrombolysis was successful in 72% of cases. Success in this context includes those in which a further procedure was possible after thrombolysis. These groups included 20 occluded grafts in which thrombolysis played an important part in unblocking 13 (65%) of them. In a separate group of 17 patients (24%) thrombolysis was given after failed angioplasty and was successful on 15 (88%) occasions. Local complications occurred in 17 patients. There were three deaths. There were no intra-cerebral haemorrhages.

CONCLUSIONS

Thrombolysis alone can be used successfully. There is a large group in which thrombolysis can help to increase the success rate of interventional radiology.