Neurology India, Vol. 59, No. 3, May-June, 2011, pp. 373-375
Topic of the issue: Editorial
Mechanical recanalization therapies for acute stroke: Advances and uncertainties
Shaloo Singhal, Velandai Srikanth, Thanh G Phan
Department of Medicine and Stroke Unit, Monash Medical Center, Monash University, Melbourne, Australia
Correspondence Address: Velandai Srikanth Department of Medicine, Level 5, Block E, Monash Medical Center, Monash University, Melbourne Australia email@example.com
Date of Submission: 22-Mar-2011
Code Number: ni11112
Stroke remains a major source of morbidity and mortality around the world, carrying with it a significant socioeconomic burden. A resurgent interest in aggressive endovascular intervention in acute stroke treatment has been stimulated by new developments in catheter and stent designs and the publication of several studies ,,, showing improved clinical outcomes from timely arterial recanalization. In this issue of Neurology India, Huded et al. present a case report demonstrating the successful use of the SOLITAIRE stent as a temporary endovascular bypass in a patient with acute carotid and ipsilateral middle cerebral artery occlusion. This report evokes a debate on the use and success of mechanical recanalization therapies in an acute stroke.
Temporary Endovascular Bypass
In the temporary endovascular bypass technique, a self-expanding stent (SES) is deployed and then recaptured after successful vascular recanalization has been restored, trapping the clot with it. This presents a novel technique, as immediate flow is restored within the vessel, thus salvaging precious penumbral tissue while avoiding the complications of permanent stent placement such as restenosis. Kelly et al.  first described a case report of this procedure in 2008, wherein an Enterprise stent successfully recanalized a right M1 occlusion after intra-arterial (IA) abciximab and rt-TPA had been unsuccessful. In recent times, Cohen et al.  described four cases of severe ischemic stroke, on a National Institute of Health Stroke Scale (NIHSS), of 18, 24, 22, 24, in whom the SES first achieved a transient bypass and then was used as a thrombectomy device. Complete recanalization was achieved in 60 minutes, required only one removal attempt, and no other thrombolytic agents. One of their patients was a 45-year-old man, with a left carotid 'T' occlusion, presenting within three hours with an NIHSS of 22. A Solitaire stent was deployed across the entire occluded middle cerebral artery (MCA) and internal carotid artery (ICA), before being retracted with the clot enmeshed. Flow was subsequently restored and the patient recovered with an NIHSS of only 2, after a week.
The safety of mechanical embolectomy was evaluated in 2004, in the single arm Mechanical Embolus Removal in the Cerebral Ischemia (MERCI) I trial,  in which 30 patients with acute stroke were treated with the MERCI clot retrieval device. Recanalization was achieved in 43% of the patients using the MERCI device alone, and in 64% of the patients who had adjuvant IA rt-PA. Recent modification to the MERCI device has increased recanalization to 70% in patients with adjuvant rt-PA in the multi-MERCI trial.  Despite there being a trend toward decreased mortality and improved clinical outcomes, these differences were not statistically significant. The MERCI device is currently approved by the FDA for thrombectomy in acute stroke. Other such devices may also come into the picture with studies, such as the Solitaire, with the intention of a thrombectomy (SWIFT) study in progress. This trial compares the efficacy and safety of the SOLITAIRE device with that of the MERCI device for thrombectomy in acute stroke.
In this issue, although Huded et al.  present a single case report of radiological success using the SOLITAIRE device for temporary endovascular bypass; we remain unclear on the patient's eventual clinical outcome. To illustrate the importance of this matter, we present another case of a 68-year-old gentleman who presented with right carotid and middle cerebral artery occlusion to our center. Despite having a completely occluded right ICA and MCA, he achieved full recanalization of these arteries solely with IV rt-TPA [Figure - 1], recovering from an initial severe deficit to be relatively free of disability (mRS 2). Although multiple case reports do present a compelling case for success of the SOLITAIRE device, both as a temporary endovascular bypass and thrombectomy device, we cannot be sure of its true efficacy without a dedicated randomized clinical trial, evaluating not just radiological recanalization, but more importantly, the clinical outcomes.
Vertebral Artery Ostium Stenting
Another important concept in recanalization is raised by Kojuri et al.  in this issue of Neurology India. They look at percutaneous transluminal angioplasty and stenting of the vertebral artery ostium (VAO). They have included patients with posterior circulation symptoms attributable to the VAO stenosis, as well as aymptomatic individuals. Although only having a short follow-up time (14 months), they have a large number of patients (n = 89) with a low complication rate (2.2%) such as dissection. Vertebral artery stenosis occurs most frequently at the vessel origin as it arises from the subclavian artery.  Surgery at this site is challenging and often associated with complications,  and therefore, endovascular stenting offers a less invasive alternative for recanalization of VAO stenosis.
To date, the Carotid and Vertebral Artery Transluminal Angioplasty Study (CAVATAS)  has been the largest trial comparing endovascular treatment with medical therapy in vertebral artery stenosis. Despite only having eight patients in each arm and a mean follow-up time of 4.7 years, the trial reveals that both groups are more likely to have a carotid territory stroke or myocardial infarction rather than a recurrent vertebrobasilar stroke. This suggests that evaluation of efficacy in such studies must include other major vascular events and stroke in other arterial territories, with the occurrence of vertebrobasilar stroke as endpoints, possibly as a combined endpoint. The study by Kojuri et al.  would have been more informative if such data had been measured and reported.
A known complication of VAO stenting is that of restenosis (defined as > 50% of arterial diameter). The Stenting of Symptomatic Atherosclerotic Lesions in the Vertebral or Intracranial Arteries (SSYLVIA) study  was a prospective, multicenter, single arm study assessing the safety of the Neurolink Stent system, comprising of balloon angioplasty and a stainless steel stent. In their sample (n = 61), six patients had VAO stenosis. Among these, restenosis occurred in 67% (defined as > 50%) of these patients at six months. In another study, Hatano et al.  stented 108 symptomatic and nine asymptomatic patients with severe VAO stenosis. Of the 104 patients that underwent repeat angiography at six months, 10 (9.6%) had restenosis, with a further two patients developing restenosis at a later point.
Another important point to consider is that, Kojuri et al. used non-drug eluting stents (NDES) in their patients. In literature, the frequency of occurrence of in-stent restenosis > 50% for VAO stenosis with NDES has ranged from 28 - 48%. ,,, In a retrospective comparison, Ogilvy et al. found a recurrent in-stent restenosis in 38% (9/24 patients) with NDES, as opposed to 17% (2/12 patients) restenosis in patients with DES. Interestingly, over 90% of the patients in both groups reported symptom improvement despite radiological progression. Other case reports ,, of VAO stenting with DES boast a low procedural complication and restenosis rate, as well as, low stroke recurrence. However, it remains unclear whether these improved outcomes are due to intervention or concurrent anti-platelet therapy. Despite their promise, these results are difficult to interpret in the absence of randomized trials, particularly given the fact that the natural history of the extra-cranial vertebral artery disease remains relatively unknown. The 5 - 11% risk of stroke or death in symptomatic vertebrobasilar disease is gleaned from patients with intracranial rather than extracranial stenoses.  Also the inclusion of asymptomatic patients with VAO stenosis in the interventional trials may lead to an inflated positive outcome, as they may have had a low or even negligible stroke risk to begin with. Of late, the American Heart Association recommended medical management only for asymptomatic carotid disease.  Asymptomatic carotid and vertebral disease may in fact represent a more diffuse process of atherosclerosis, and therefore, may be better managed with a systemic rather than focally oriented approach.
In conclusion, new mechanical recanalization therapies such as temporary endovascular bypass and VAO stenting provide an exciting new forefront in the field of interventional stroke. However, without sufficient data on the natural history of these conditions and a relative paucity of randomized controlled trials, we are yet to understand the true impact of these interventions with regard to patient outcomes.
Copyright 2011 - Neurology India
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