In this retrospective study, we examined the safety and effectiveness of a modified STR technique for removing migrated emboli in the M2, M3, A2, and A3 segments during mechanical thrombectomy for acute LVO. Although a prospective randomized study has not yet conclusively established the safety and effectiveness of mechanical thrombectomy beyond the proximal segment, the American Heart Association and American Stroke Association (AHA-ASA) currently recommend it as a viable treatment option for selected patients. This recommendation is based on evidence from subgroup analyses of five randomized trials and meta-analyses [8, 20, 21]. Some studies have also suggested that untreated distal occlusions could progress into significant ischemic areas [4, 6–8, 21]. Interestingly, recent reports have demonstrated favorable outcomes with a higher reperfusion rate in distal arterial occlusions, such as M2-3, A2-3, and P2-3, using smaller instruments and experienced techniques. These reports did not show statistical differences in procedure-related complications, such as symptomatic ICH, vascular dissection, or perforation, compared to the treatment of proximal occlusions. Furthermore, they indicated clinical improvement by achieving better TICI scores through effective treatment of DVO [11–13, 15, 20].
Refining the approach to secondary DVOs that manifest during a procedure is crucial, given their conceptual distinctions from primary DVOs. Despite these differences, secondary DVOs often manifest with severe clinical symptoms, aggravated neurological deficits, larger ischemic extents, and increased clot fragility.[10] In a pioneering meta-analysis of safety and efficacy outcomes related to mechanical thrombectomy involving STR and aspiration in secondary DVOs, Rodriguez-Calienes et al. examined data from 14 studies encompassing 291 patients. Their findings revealed favorable outcomes, with a successful reperfusion rate (mTICI, ≥ 2b) of 82% and a symptomatic ICH rate of 6% [22].
Liu and colleagues identified a distinctive interaction between thrombus and stent retriever in the context of utilizing primary stents for DVOs and observed that the connection is superficial rather than the thrombus merging into the stent retriever, particularly when the embolus partially extends into the stent through its mesh [6]. In such cases, the stent, with its smaller diameter and narrower mesh, grips the embolus during partial retrieval. In our modified STR approach for local DVOs, the primary objective is to reduce the frictional force between the stent and the parent artery, minimizing the risk of vascular injury during the procedure. From our perspective on the modified STR technique in the local DVO, the aim is to decrease the frictional force between the stent and the parent artery, thereby minimizing the potential for vascular injury during the procedure. To achieve this, we recommend using stents like Trevo ProVue 4 x 20 mm and Solitaire Platinum 4 x 20 mm for vessels with a diameter of 2 to 4 mm. However, when applied in vessels with a diameter of 2 mm or less, retrieving the entire stent with its original radial force can often induce traction or shearing stress on the targeted vessels. Considering that migrated clots in distal vessels are usually fragmented into smaller sizes than primary clots, the radiopaque property of these stents allows operators to control friction at the M2 to M3 and A2 to A3 segments by adjusting the covering length of the microcatheter. After fully deploying the stent at the DVO to enhance clot entrapment, the microcatheter can be re-sheathed while providing local compression on the stent, confirmed by jammed resistance in the retrieval system.
The deployment of low-profile stents and aspiration catheters, such as Baby Trevo, Catch Mini, various intermediate catheters, and Penumbra 3 or 4 Max, has shown promising outcomes in terms of both successful recanalization rates and one-pass success rates in cases of DVO [11–13, 20, 23]. Consistent studies have reported a meaningful success rate in vascular recanalization (TICI ≥ 2b), approximately ranging from 76–85%. This underscores the efficacy of these low-profile devices in effectively reopening obstructed blood vessels. Furthermore, the one-pass success rate, indicating successful vascular recanalization in a single attempt using these devices, has been reported to be approximately 48–60%. In a comparative analysis of favorable outcomes associated with these innovative low-profile devices in DVO treatment, our research reveals highly comparable and, in some respects, more impressive results. Specifically, it demonstrated a significantly higher success rate of mTICI 2c-3 reperfusion, accomplishing this outcome in 23 of 24 patients (95.8%) at the final recanalization stage, coupled with a superior one-pass success rate of 70.8%.
Based on the available data, the reported rates of complications associated with supplementary procedures for secondary DVO align with findings from previous thrombectomy investigations [22, 24–26]. Specifically, procedure-related vascular injuries have been reported in approximately 1–2% of cases, while post-procedural hemorrhagic tendencies have been observed in 4% of instances. Notably, this study identified the incidence of vessel spasm and dissection to be less than 1%, with these complications effectively addressed without resulting in severe consequences. Moreover, severe hemorrhagic changes linked to the procedure were also found to be less than 1%, indicating a low risk of significant bleeding complications. The occurrence of asymptomatic ICH was relatively rare, and importantly, no instances of neurological deterioration were observed in the patients. These findings robustly support the contention that the modified STR procedure represents a generally safe option, characterized by low complications and a favorable risk profile.
When restoring blood flow to salvage brain tissue within an appropriate timeframe, the overall vascular distribution plays a crucial role in determining the extent and progression of cerebral infarction [27, 28]. Several studies have reported that the initial status of collateral circulation significantly influences the size and scope of cerebral infarction, as well as the ultimate clinical outcomes following mechanical thrombectomy [29, 30]. In the 24-hour follow-up diffusion-weighted image results assessing the occurrence of cerebral infarction after modified STR, individuals with good collateral status (8 cases) experienced partial infarction in 1 case, those with moderate collateral status (9 cases) exhibited partial infarction in 1 case, complete infarction in 2 cases, and those with poor collateral status (7 cases) had partial infarction in 1 case and complete infarction in 6 cases. At the 3-month follow-up, neurologically favorable outcomes were observed in 12 out of 13 cases without local infarction, 2 out of 3 cases with partial cerebral infarction, and 2 out of 8 cases with complete cerebral infarction. This suggests that, under certain circumstances with favorable initial collateral circulation, additional intervention with modified STR for DVO may lead to improved clinical outcomes.
Furthermore, it offers advantages in terms of efficient time management and cost-effectiveness. Reported average procedural times for small-profile stents ranged from approximately 70–80 min, while aspiration catheters with a small diameter demonstrated procedural times of approximately 42–67 min for primary DVO [11–13, 31]. In this specific context, the average procedure time for the modified STR technique was 23.2 ± 14 min, indicating a notably shorter duration compared to previous results targeting DVOs. These variations naturally depend on the preparation of the guiding and additional devices. Essentially, the stent initially employed for LVO can be utilized for secondary DVO without the need for additional tools. This repetitive use not only provides financial benefits to specific patients but also offers a practical solution for DVO, particularly in countries with limited reimbursement policies for available devices.
This study has some limitations that should be considered. First, the retrospective design and relatively small sample size limit the generalizability of our findings. However, it is important to note that all data related to angiographic or clinical outcomes were prospectively registered in a core lab, ensuring the validity of the collected information. Second, the decision to perform the modified STR technique at the new embolic territory was based on the discretion of each neurointerventionalist, which may introduce a selection bias. Nonetheless, it is worth mentioning that all physicians involved in the study had extensive experience in performing mechanical thrombectomy for over 10 years, and the technique was a consensus among them in similar situations. Although the modified STR technique demonstrated promising application and reliable results for secondary migrated emboli beyond the proximal segment, further investigation is warranted to assess its specific benefits. Prospective comparisons with small-profile devices in primary DVO cases would provide a more comprehensive understanding of its efficacy and safety.