Abstract and Introduction
Abstract
In recent years, endovascular self-expanding stents have become a viable option for neurointerventionalists treating acute ischemic stroke. Timely intervention for stroke could mean the difference between complete recovery and significant morbidity or death. Since 2006, a handful of clinical trials have demonstrated the potential of self-expanding stents in dependably achieving quick revascularization. These devices are expanding in utilization as new designs offer greater procedural flexibility and better clinical results. We discuss these clinical investigations, focusing on the procedural capabilities and limitations of each self-expanding stent design.
Introduction
Despite advances in therapy, stroke remains the third leading cause of death in developed countries. An estimated 795 000 strokes occur annually in the USA, with ~15%–30% of survivors suffering permanent disability. The total estimated financial burden associated with stroke in the USA rose to $73.7 billion in 2010. Current treatment modalities for acute ischemic stroke (AIS) include pharmacological and mechanical thrombolysis, although these strategies are still being perfected. Intravenous tissue plasminogen activator (tPA) is the only FDA-approved pharmacological intervention in the setting of acute stroke. The National Institute of Neurological Disorders trial found that this therapy benefited patients with AIS if tPA was administered within 3 h of symptom onset; more recent data have extended this therapeutic window to 4.5 h. In the field of endovascular intervention, two mechanical devices have gained FDA approval for the treatment of acute stroke. The Merci clot retrieval device (Concentric Medical, Mountain View, California, USA) has shown promise, achieving 69.5% vessel recanalization (Thrombolysis In Myocardial Infarction (TIMI) grade 2–3 flow) with adjuvant intra-arterial tPA in the Multi-MERCI trial. Additionally, the Penumbra thromboaspiration catheter (Penumbra, Inc., Alameda, California, USA) achieved an 81.6% recanalization rate (TIMI grade 2–3 flow), though a significant number of complications (intracranial hemorrhage (ICH) rate of 28% within 24 h of treatment) were observed in the Penumbra Pivotal Stroke Trial.
In light of the limitations of these currently approved therapies, stenting devices have become an increasingly attractive treatment option for AIS. Modern endovascular stenting began with the work of Charles Dotter in the 1960s, and in 1983 Dotter and Andrew Cragg published simultaneous studies demonstrating coil-shaped stents used to treat arterial stenosis. Through the 1980s and 1990s, cardiologists developed balloon-mounted stents (BMSs) to treat chronic and acute coronary diseases. Continuing the upward anatomical trend, BMSs were used in the mid- to late 1990s to treat carotid artery stenosis and intracranial aneurysms. Despite the extensive use of stents to obliterate acute occlusions in coronary arteries, similar neurovascular interventions did not become common until 2006. These first case studies detailed how BMSs could treat AIS in a similar manner to acute coronary interventions. Later that year, Levy et al demonstrated the feasibility of this technique in a series of 19 patients with AIS. Their efforts led to a 79% recanalization rate (TIMI grade 2 or 3), with only one ICH and mortality of 26%. A statistical analysis later in 2006 by Gupta et al showed that stenting with angioplasty was an independent predictor of recanalization in occluded intracranial arteries. The results of these studies preempted the design of stents intended specifically for use in the neurovasculature. Eventually stents designed for the express purpose of recanalization of stenotic intracranial arteries emerged. These self-expanding stents (SESs) constitute a promising advance in therapy for AIS. These devices and others like them, potentially provide improved capability in obtaining timely arterial reperfusion, as evaluated in several clinical reports published in the past few years. We discuss the development and study of these stents, highlighting modifications in design and delivery mechanisms that have increased safety and efficacy.
The reader is referred to Table 1 for details of each clinical study, including recanalization rate, complications and mortality.