(Circulation. 2001;104:2.)
© 2001 American Heart Association, Inc.
Editorials |
Carotid Filters
New Additions to the Interventionist’s Toolbox
From the Division of Cardiology, Department of Medicine, Rhode Island Hospital, Brown University, Providence, RI.
Correspondence to David O. Williams, MD, Division of Cardiology, APC 814, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903. E-mail dowilliams{at}lifespan.org
Key Words: Editorials • carotid arteries • atherosclerosis • stents
Although percutaneous, catheter-based treatment for atherosclerotic arterial obstruction began in the peripheral circulation, usage became widespread only after coronary application. The procedure’s abilities to relieve angina and either spontaneous or provoked myocardial ischemia and to achieve prompt reperfusion in myocardial infarction are well-documented.1 Even selected patients with advanced, multivessel coronary disease can expect outcomes similar to those provided by the more invasive bypass surgery.2 3 4 Now, enthusiasm for catheter revascularization is circling back to arteries beyond the coronary circulation.
Among these new targets are the carotid arteries, which are well recognized as sources for cerebral emboli, a major cause of stroke. Surgical endarterectomy is performed for severe, symptom-related carotid atherosclerosis and, in selected asymptomatic patients, it seems superior to medical treatment alone in preventing stroke.5 6 7 Using approaches and techniques developed from coronary intervention, clinician-investigators have demonstrated that balloon angioplasty and stent deployment are feasible for narrowings involving the internal and external carotid and its bifurcation. Initial observational results are encouraging to the point where a direct comparison of catheter-based therapy to carotid endarterectomy has begun in the form of a large, multicenter, randomized, clinical trial.8
Distal embolization of atherosclerotic debris as a consequence of balloon angioplasty has been an issue of concern since the inception of the procedure. Fearful of emboli, Andreas Gruentzig drained, filtered, and examined blood from the coronary sinus when he first performed coronary balloon angioplasty in man (Andreas Gruentzig, MD, personal communication, August 1978). With the exception of degenerated saphenous aortocoronary vein grafts and native arteries with substantial intracoronary thrombus, however, clinically significant embolization resulting from balloon angioplasty alone or with stent deployment is not a major concern in the coronary circulation.
Such may not be the case with carotid intervention. Strokes, both major and minor, are acknowledged complications of carotid stenting, and the mechanism now seems to be embolic, rather than the acute occlusion or dissection that was observed during the early balloon angioplasty experience.9 Of special note are the success and complication rates of carotid artery stenting that have been observed with the development of the technique. As reported by Roubin et al,10 success rates of 98% are now achievable, and the incidence of minor strokes seems to be declining. What does not seem to be declining, however, is the incidence of procedure-related major stroke. Thus, in the first year of their experience, the major stroke rate was 1%; the rate was 1.2% in their fifth year. This issue is one of substantial concern given the grave consequences of major stroke, the low rate observed with alternative therapy, and recognition that avoidance of stroke is the reason for doing the intervention in the first place.
In this issue of Circulation, Reimers et al11 report their experience of performing carotid stent implantation with the aid of filter devices. These devices are miniaturized baskets or sieves that are attached to the guidewire used for delivering balloon and stent catheters. They are located near the distal end of the wire, downstream from the site of balloon inflation and stent implantation. When fully expanded, these filters capture any upstream debris. Special retrieval catheters collapse the filters and enable removal without loss of trapped material. The present report describes an experience using distal filter protection devices in 84 patients treated with carotid stents. From a procedural perspective, device placement was possible in all but 3 attempts. Debris was visible within the filters in 53% of cases. One minor stroke (1.2%) was observed over 30 days of observation. There were no major strokes.
What conclusions can be drawn from this report? First, the investigation demonstrates that temporary deployment and retrieval of distal protection devices in the carotid circulation is feasible and safe. Second, carotid stenting results in the embolization of visible, atherosclerotic debris, and some or possibly all of this material can be captured and removed with a distal protection device. Of significance, embolization was observed in at least half of the patients.
Are there important questions that remain unanswered? Certainly. The real purpose of distal protection is to prevent embolization sufficient to cause stroke. Given the relatively small number of patients studied, coupled with the low 1% stroke rate in the absence of distal protection, a much larger investigation will be required to determine whether stoke is less likely with distal protection than without it. Could stroke develop even if these devices successfully trap all macroscopic material? Hypothetically, yes. A shower of small particulate matter could cause microvascular obstruction. Furthermore, particles or vasoactive substances contained within plaque or thrombus could cause intense, prolonged vasospasm and subsequent cerebral infarction. Of the various devices available, is there one that is superior? Although 3 separate devices were evaluated, data to characterize performance differences are lacking. With this new information in hand, can carotid stenting now be considered equivalent to endarterectomy? This critical question still needs to be answered by a head-to-head comparison in the form of a randomized clinical trial. Given the information presented by Reimers et al,11 however, such an investigation should consider including distal protection devices in the carotid stent arm. The field of percutaneous vascular intervention is dynamic12 and, for comparisons to be legitimate, technical advances should be incorporated into formal scientific studies.
In the final analysis, the findings of this brief report are encouraging and provide support for the further evaluation of percutaneous catheter-based therapy for cerebrovascular disease.
Acknowledgments
The author thanks Arlene S. Grant for her assistance in the preparation of this manuscript.
Footnotes
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
References
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