<International Circulation>: Mechanical thrombectomy is increasingly being used for the treatment of large-vessel ischemic stroke in patients who arrive outside of the 3-4.5 hour tissue plasminogen activator time window. Could you give us a brief introduction of the use of mechanical thrombectomy in your country?
Prof. Lutsep: This is something that we have been working on for about ten years trying various ways to remove clots but it wasn’t until 2004 that the MERCI retriever was approved by the FDA. Since then， it has become the most commonly use system. The one other system that is approved is the PENUMBRA device. It applies aspiration to the clot whereas the MERCI retriever is a like a corkscrew that pulls out the clot.
<International Circulation>: Do we have evidence that these devices will improve outcomes in patients with ischemic stroke?
Prof. Lutsep: That has been one of the big questions raised because there has not been a randomized trial using these devices. The main evidence that we have is that in every single study that if the vessel opened the patients were more likely to have a favorable outcome than in the patients whose vessels remained occluded and mortality rates were much lower as well.
<International Circulation>: What is the difference between the first generation mechanical devices for clot removal， the MERCI device and the new generation device PENUMBRA system?
Prof. Lutsep: There are really two that are being asked. The MERCI device itself has been changed over time. For example， in the MERCI trial compared to the Multi MERCI trial， the design of the device was changed. Even since then there have been new iterations of the MERCI retriever device. It is still based on the corkscrew concept where it releases these loops into the clot and pulls the clot out. The PENUMBRA device works on a different basis in that it applies aspiration to the clock. Therefore， the two devices have different mechanisms.
<International Circulation>: What are the risks of treatment with the clot retriever in patients with cerebral infarction?
Prof. Lutsep: There certainly are potential risks but they have been low in the trials. One risk is that despite efforts to prevent pieces of debris from going downstream and affecting other vessels， sometimes that can happen and a piece of a clot can cause a vessel occlusion further down in the vascular bed. There are ways to reduce it from happening by blocking flow proximally to encourage the emboli to be pulled out rather than going in the wrong direction. Another risk is that as these devices are placed in the vessel they can pull on the vessel and can cause it to tear in some cases and that may or may not have consequences. What we worry about is that sometimes it can tear enough that the vessel can leak and cause a hemorrhage.
<International Circulation>: Do you think that surrogate end points (i.e. recanalization of a cerebral vessel) would be sufficient to determine approvability of a device? Neurological outcome， which should be the most important outcome in a stroke treatment trial， was a secondary end point in the MERCI study and was determined by comparing the outcome of treated patients to the placebo arm of PROACT II.
Prof. Lutsep: I am a neurologist therefore I am most interested in neurological outcomes. There are two main reasons that it has been difficult to compare the trials. We have used PROACT as a historic control. This sets a very high bar because the patients were less severely affected in PROACT than they were in the mechanical device trials because PROACT only included patients with middle cerebral artery strokes. The fact that it appeared that outcomes tended to be better than the patients in the non-treatment arm is encouraging， but you are comparing two very different things. Also， we are comparing two very different times in history and we are much better at treating strokes today. It would be ideal to have a head to head comparison and a randomized control trial. However， it is very expensive to conduct a trial like that and the longer these devices are on the market the more reluctant people are to randomize patients to lesser therapies.
<International Circulation>: Is there an ethical problem with randomizing patients to those arms with lesser therapies in that kind of trial?
Prof. Lutsep: There is still enough of a question without a randomized trial that you can argue that you could still do that. However， it is a real dilemma. Frequently， patients are transferred from far away to our hospital and it is hard to tell them that they are going to receive a lesser treatment.
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