In an in vitro stroke model comparison, the use of the Cover accessory device (Lazarus Effect) in conjunction with a stent retriever resulted in higher successful recanalisation rates, no embolic events and proved to be more effective than the use of a conventional guide catheter or a balloon guide catheter.
The recently CE mark approved Cover device is a nitinol braided mesh that surrounds the stent retrieval device and its captured thrombus during retrieval to help prevent clot fragmentation and embolisation.
In their investigation, published in the Journal of NeuroInterventional Surgery, Maxim Mokin and colleagues used a previously developed cerebrovascular model with intracranial circulation based on patient derived anatomy, into which they introduced fresh clot into the middle cerebral artery, to compare rates of target vessel recanalisation and embolisation in new (non-affected and distal) territories (areas in which clot had not been introduced) achieved with a stent retriever (Solitaire flow restoration device, Medtronic) in conjunction with the use of a conventional guide catheter (control group), a balloon guide catheter (BGC group), and the Cover device (Cover group).
According to the investigators, the Cover device is employed as follows: “First, the stent retrieval device is delivered and unsheathed to capture the thrombus. Next, the stent retriever delivery microcatheter is removed. The Cover device is loaded and delivered over the 0.014-inch stent retriever. An intermediate catheter can be used to facilitate the delivery process in cases with tortuous anatomy of the intracranial vasculature. Withdrawal of the stent retriever causes the mesh of the Cover device to invert, wrapping around the stent retriever and protecting the clot from fragmentation.”
In the study, the control group consisted of thrombectomy experiments performed using a conventional guide catheter (6F Cook shuttle, Cook Medical), which was placed into the segment corresponding to the cervical internal carotid artery. In the BGC group, thrombectomy was performed with an 8F balloon guide catheter (Merci, Concentric Medical/Stryker Neurovascular, or Cello, Covidien/Medtronic). The balloon was inflated prior to withdrawal of the stent retriever, and manual aspiration was applied using a 20mL syringe. Finally, in the Cover device group, an intermediate catheter was utilised (0.057 inch distal access catheter, Concentric Medical/Stryker Neurovascular) to facilitate delivery of the Cover device. The investigators write that no aspiration was applied through the intermediate catheter of the guide catheter while thrombectomy was attempted.
Primary outcomes included the degree of recanalisation and the occurrence of emboli in a new, previously unaffected territory in which clot was not introduced.
The authors report on a total of 51 thrombectomy experiments (20 in the control group, 20 in the BGC group and 11 in the Cover device group). “Successful delivery and inversion of the Cover device around the stent retriever was achieved in all cases. Successful recanalisation (TICI 2b-3) on first pass was achieved in 50% of control cases, 45% of BGC cases and 91% of Cover device cases.” This is quite impressive, the authors say, given the fact that most previous stent retrieval trials required multiple passes for final results.
They further state that the rate of successful recanalisation was similar between the control group and the BGC group, occurring in 10 of 20 versus nine of 20 experiments, respectively (p=0.020). In comparison, successful recanalisation was achieved more frequently in the Cover device group, occurring in 10 of 11 experiments.
No embolisation of new territories was seen with the use of the Cover device. On the other hand, the authors report that embolisation occurred in five (25%) experiments from the control group and in three (15%) experiments from the BGC group.
Mokin et al state, “Our in vitro results demonstrate that the use of the Cover device was more effective than the use of the BCG with respect to reducing the number of embolic events, thus leading to higher recanalisation rates. Moreover, adjunctive use of the Cover device does not prolong the duration of the interventional procedure.”
Study author Adnan Siddiqui (University at Buffalo, State University of New York, Buffalo, USA) spoke to NeuroNews about the way forward.
What is the next step in your research?
The recent trials have demonstrated that stent retrieval has clearly passed superiority to intravenous thrombolytics or best medical therapy. However, when we look at good outcomes they achieve only 35% in unselected cohorts such as MR CLEAN and the best we can do with careful selection based on perfusion is 60% -70% as shown in SWIFT PRIME, ESCAPE and EXTEND-IA. This means that despite careful selection of patients most likely to benefit we are failing in up to 40%. We believe that multiple passes, clot fragmentation with emboli in non-affected and distal territories play a major role in these poor outcomes. We plan to study different strategies for rapid and complete revascularisation using this model, which duplicates not only proximal arch, cervical and intracranial tortuosity but also collaterals which naturally exist in the form of ACom and Pcom arteries.
Do you think that the Cover device, or similar devices, will be used in conjunction with stent retrievers in all thrombectomy procedures in the future?
We believe that stent retrievers are the next iterative step in the evolution of the optimal stroke revascularisation strategy. We suspect that we would need a tool kit for fastest and most complete revascularisation. Clearly, addition of the Cover device almost doubles the effectiveness of the first pass and significantly enhances embolic protection during use of current stent retrievers in our in vitro stroke model. We believe given the high degree of corroboration between device effectiveness in patients and its replication in our model that we would expect similar results in patients. We look forward to results from clinical usage of the Cover device.