Does it Work?
The central theme of this controversy is not controversial! We all agree that recanalization is the most important target for therapy in acute ischemic stroke because it undoubtedly improves outcomes. The caveats are that recanalization needs to be performed within a time window to salvage significant penumbral tissue and that safety (hemorrhagic transformation and maintenance of vascular integrity) is within reasonable limits. So where does this place mechanical recanalization with the Merci Retriever?
Since the introduction of IV thrombolysis a decade ago, we have improved our understanding significantly of the processes involved in site and responsiveness to therapy. For example, we now know that the recanalization rate for large proximal vessels is poor.1 Also, all clots are not the same. As pointed out by Saver, there is an order of magnitude difference in the volume of proximal and distal thrombi in the internal carotid/middle cerebral axis, correlating with the likelihood of successful recanalization. It, therefore, appears rational to us that decision algorithms for individual patients (IV versus intra-arterial thrombolysis versus mechanical recanalization) should be based on an understanding of individual patient pathophysiology.
Although the focus of the discussion of our protagonists has been on arterial recanalization, we would also suggest that a broader imaging strategy should include identification of the presence and extent of the ischemic penumbra.2 Clearly, expensive therapeutic efforts to recanalize vessels is probably not warranted if there is no penumbra to salvage. Hence, in the future, we will be moving toward a total evaluation of arterial and tissue status in individual patients, regardless of time of stroke onset, with the aim of individualizing therapy.
To return to our controversy, does the Merci Retriever work? In spite of his passion, Saver quite rightly tempers his comments, echoed by Wexler, that these are early days, and that large clinical trials are needed to determine the clinical safety and efficacy of this exciting technology. Even with mechanical retrieval using the Merci device, recanalization was only achieved in 46% of patients, mortality was 44%, and symptomatic intracerebral hemorrhage occurred in 7.8% of patients, comparable to IV tPA.3 Early days indeed!
An issue not raised in this controversy is the resource implication of a successful translation of this technology into practice. Obviously, few patients are likely to have access to facilities where this procedure could be used. Generalizeability will, therefore, become a real issue if further clinical trials prove that the Merci device does work with an acceptable safety profile. Stroke clinicians should be aware that primary coronary angioplasty is superior to thrombolysis for acute coronary syndromes and is routine in many centers around the world.4 We should not resile from our responsibility to our patients in pushing this technology forward.
- Received January 24, 2006.
- Accepted February 3, 2006.
Ly HQ, Kirtane AJ, Buros J, Giugliano RP, Popma JJ, Antman EM, Harrington RA, Ohman EM, Gibson CM; TIMI Study Group. Angiographic and clinical outcomes associated with direct versus conventional stenting among patients treated with fibrinolytic therapy for ST-elevation acute myocardial infarction. Am J Cardiol. 2005; 95: 383–386.
Smith WS, Sung G, Starkman S, Saver JL, Kidwell CS, Gobin YP, Lutsep HL, Nesbit GM, Grobelny T, Rymer MM, Silverman IE, Higashida RT, Budzik RF, Marks MP; MERCI Trial Investigators. Safety and efficacy of mechanical embolectomy in acute ischemic stroke: results of the MERCI trial. Stroke. 2005; 36: 1439–1440.
Derex L, Nighoghossian N, Hermier M, Adeleine P, Berthezene Y, Philippeau F, Honnorat J, Froment JC, Trouillas P. Influence of pre-treatment MRI parameters on clinical outcome, recanalization and infarct size in 49 stroke patients treated by intravenous tissue plasminogen activator. J Neurol Sci. 2004; 225: 3–9.