In a session of the 2020 Cardiovascular and Radiological Society of Europe (CIRSE) meeting (12–15 September, virtual) focused on the hottest news in the endovascular thrombectomy space, Antonin Krajina (University Hospital, Hradec Králové, Czech Republic) shared new devices available for the procedure, and enthused about their potential in stroke management.
First describing his, hypothetical, ideal device for endovascular thrombectomy, Krajina said that it should be “easy to use and have fast access to the clot”. Stent retrievers are assessed by their ability to integrate the clot and to keep hold of it during retrieval; radiopacity of the stent retriever therefore plays an important role, Krajina stated. Additionally, he explained how there is a significant association between first-pass complete reperfusion and favourable clinical outcome, with two to three times higher odds for a favourable clinical outcome compared with complete reperfusion after multiple passes.
Indeed, his key take-home message was that clot integration is a function of delivery technique, duration of device implantation, and clot mechanics. His talk therefore detailed how device design influences these aspects of performance. In addition, he urged his listeners to “use all tricks in the attempt to remove the clot at the first pass (including aspiration via balloon guide), and detailed how the COMPASS trial results provide Level 1 data that an aspiration thrombectomy as first-pass approach is non-inferior to a stent-retriever as a first-line approach for the treatment of selected patients with acute large vessel ischaemic stroke.
The importance of device design
Comparing the Solitaire X device (Medtronic), the CatchView stent retriever (Balt), and the Embotrap III device (Cerenovus), Krajina showcased how each had platinum markers on the proximal and distal ends, explaining that these acted as radiopacity markers.
Turning to the capacity to integrate the clot, he next discussed the relative benefits of using a short (20mm) or a long (30mm) stent retriever: “A longer [stent retriever] may increase the capacity to catch the clot,” he said. This was proven by Gaurav Girdhar (Medtronic, Irvine, USA) et al in their January 2020 publication in Interventional Neurology, which concluded that stent length had a significant effect on first pass success rate (p<0.05). The authors wrote: “Longer stent retrievers may be safe and effective in improving first pass success for fibrin-rich clots in vitro and in vivo models of large vessel occlusion”. However, Krajina added that a longer stent retriever means higher friction, which in turn increases the probability of the device getting stuck and then elongating, resulting in a loss of apposition to the arterial wall. The embolisation risk of the clot is also higher with longer devices, he explained, as longer dwell times affect the likelihood of distal embolization.
“Stent retrieval length should be adjusted to clot extent,” Krajina said, citing a June 2020 paper published in Cerebrovascular Diseases from Hanna Styczen (University Hospital Essen, Essen, Germany) and colleagues. Styczen et al hypothesised that increased stent retriever length may improve the rate of complete angiographic reperfusion and decrease the respective number of attempts, resulting in a better clinical outcome. They conducted a retrospective analysis of 394 patients with large vessel occlusion in the anterior and posterior circulation treated with stent retriever mechanical thrombectomy, sorting patients by propensity matching into two groups: those treated with a short (20mm) device, and those treated with a long (30mm) device. They found that, in the anterior circulation, short stent retrievers had a significantly higher rate of first-pass reperfusion in cases with low clot burden, and in middle cerebral artery occlusions. Higher rates of favourable outcome at discharge and 90 days were observed for the short stent retriever group (p<0.001). This led them to conclude, as Krajina related to the CIRSE audience, that stent retriever length “should be adjusted to clot burden score and vessel occlusion site.” Krajina clarified: “Stents for short occlusion are appropriate if they are 20mm long; for longer occlusions, we need longer stent retrievers.”
“What position of the stent-retriever in relation to the occlusion/ embolus is the most effective?” Krajina asked his listeners rhetorically. “If it [the stent-retriever] is too –proximal and/or only partially engaged into the clot, it is less probable that we can remove the whole clot,” he explained. “If the clot is more proximal to the stent-retriever, the probability that we remove it during first-pass is higher. To verify the relationship of the clot and the stent-retriever position, we perform an angiogram after stent-retriever deployment.”
Next, Krajina discussed how to decide what diameter stent-retriever device to use to increase the probability of successfully removing the clot at first pass, 4mm or 6mm. “If you look at a diameter of the M1 segment in males, it is about 2.5mm, and the diameter of the internal carotid artery is around 3mm,” he informed delegates.
Writing in the Journal of Neurointerventional Surgery in 2018, Mark Davison (Rush University Medical Center, Chicago, USA) and colleagues said: “Compared with males, females consistently fare worse following mechanical thrombectomy for large vessel ischaemic strokes. Understanding why this gender disparity occurs may guide improvements in future treatment strategies.” In their study, they aimed to determine whether gender differences in cerebral arterial diameter correlated with clinical outcomes following stroke thrombectomy. They therefore performed an observational study of 92 consecutive acute ischaemic stroke patients (42 women) undergoing mechanical thrombectomy between June 2013 and August 2016 at a single, urban tertiary care medical centre. Catheter angiographic images were used to manually measure proximal segment arterial diameters in a standardised fashion, and medical record review was used to obtain relevant independent and dependent variables. Internal carotid artery terminus diameters for men and women were 3.08mm and 2.81mm, respectively (p=0.01). M1 segment middle cerebral artery diameters for men and women were 2.47mm and 2.18mm, respectively (p<0.0001). Nearly half (48%) the patients in the upper middle cerebral artery calibre tercile attained a favourable mRS 90-day value compared with 35% in each of the lower and middle terciles (p=0.51). Larger middle cerebral artery diameters correlated with favourable discharge disposition (p=0.21).
This led Davison et al to conclude: “These results provide limited evidence that males have larger cerebral arterial diameters than females and that larger arterial diameters may improve the odds for favourable clinical outcomes. If future studies validate these findings, arterial diameter may become a relevant variable in the design of improved thrombectomy strategies.”
However, Krajina went on to say that “More and more studies are proving that stent-retrievers with larger diameters do not appear to provide clear benefits”. Detailing a 2017 paper published in the American Journal of Neuroradiology, he reported how, in their investigation of the effects of different diameters of Solitaire retrievers on clinical outcomes, Dong Yang (Jinling Hospital, Second Military Medical University, Nanjing, China) and colleagues found “no evidence of a differential effect of intra-arterial therapy based on the size of the stent-retrievers”. Though they also found that, in patients with atherosclerotic disease, favourable reperfusion was associated with deployment of a small stent.
Demonstrating new designs for stent retrievers that he believes are improving interventionalists’ ability to successfully perform endovascular thrombectomy, Krajina introduced the NeVa stent retriever from Vesalio, which has clot pockets oriented at 90 degrees to each other that increase the first-pass effect. The Embotrap III device (Cerenovus) has an inner channel to stabilise the clot during retrieval, and an outer cage to engage and integrate the clot. With this latest re-design, the distal mesh of the Embotrap III device is also denser than previous iterations.
Access and delivery catheters and guidewires
“Besides stent-retrievers, we also need delivery catheters and guidewires,” Krajina said. In his view, the most important aspects to consider for these devices are navigability, pushability, kink resistance, and whether or not they can be assembled as a coaxial set.
A survey of Society of Neurointerventional Surgery (SNIS) neurointerventionalists that received 78 responses (approximately 10% of SNIS membership), published in the Journal of Neurointerventional Surgery, indicated an increase in aggressiveness in pursuing thrombectomy based on selection criteria. Nearly 40% of respondents (39.7%) reported using catheter aspiration thrombectomy as a frontline therapy. A further 28.2% opted for stent-retriever mechanical thrombectomy, and another 28.2% said they adopted a combined approach, utilising stent-retrievers with aspiration.
“Interventional neuroradiologists love to combine access catheters to create coaxial double, triple systems,” Krajina told CIRSE registrants, “sometimes in difficult or tortuous anatomy, referred to as a ‘tower of power’, to have enough support for intracranial catheters.” To create such a set, the length and diameter of the catheter used is important, the CIRSE audience heard: “Ideally one should use the shortest length necessary to do the job.”
Finally, he stressed that interventionalists should use balloon-guiding catheters to stop arterial flow, and to facilitate aspiration via these catheters during clot removal.