Key-words:
Clot capture - mechanical thrombectomy - push-and-fluff - stent retriever
Introduction
Generally, in vitro training for neuroendovascular intervention is challenging. Practicing coil embolization and liquid injection using simple equipment is difficult. For example, the push-and-fluff technique [[1]] depends on a physician's skill. Conversely, the confront clot scrambling method (CCSM)[[2]] can be repeatedly performed to practice mechanical thrombectomies at any location and time using inexpensive equipment. One advantage of the CCSM is that it allows the degree of stent dilatation to be evaluated by direct visualization. In this experimental study, we evaluated the accuracy of the CCSM using an equitable automatic withdrawal machine to optimize the training process for beginners.
Materials and Methods
Six standard stent retrievers of three different brands, as used in a previous report,[[2]] are evaluated as listed in [[Table 1]]: The Trevo ProVue (Stryker, Kalamazoo, Michigan, USA; three sizes), Revive (Codman, Raynham, Massachusetts, USA; one size), and Solitaire 2 (Medtronic, Irvine, California, USA; two sizes).
Table 1: The Trevo ProVue (Stryker, Kalamazoo, Michigan, USA; three sizes), Revive
Confront clot scrambling method
Experiments were performed in dry conditions at room temperature. A piece of urethane gel was used as a model thrombus to circumvent the konjac-associated risk of spoilage during the humid season in Japan. A polyvinyl chloride tube (5 mm in diameter and 20 cm long) was used to model the vasculature. A 15-mm long sham clot was placed in the middle part of the tube. Thereafter, two stent retrievers were simultaneously navigated and deployed from each side to reach come into contact with the sham clot [[Figure 1]]. Then, both stents were simultaneously withdrawn from each end with an equal force generated by an equitable automatic withdrawal machine [[Figure 2]]. It was determined that the stent, which successfully removed the sham clot, had superior clot-retrieval ability [[Figure 3]].
Figure 1: Schematic illustration of the confront clot scrambling method showing an artificial positioned in the middle of the tube. Then, two stent retrievers were inserted (one from each side) to contact the clot. Next, each stent was simultaneously withdrawn with the same speed, from each end, using automatic withdrawal machines
Figure 2: Photographs of the equitable automatic withdrawal machines. Black arrows indicate actuator machines. The stent delivery wires were simultaneously withdrawn to the opposite side at speed of 1.0 mm/s. Black arrowhead shows the over-hang charge-coupled device video camera
Figure 3: Photographs of the confront clot scrambling method using the machines with two stent devices. (a) The state just after stent deployment. Both stents were simultaneously deployed. The right stent was deployed using the push and fluff technique. (b and c) When both stents were withdrawn, with the same force from each end using the machines, the clot was retrieved by the right stent
Automatic withdrawal machines
Multiple machines, each using a linear actuator to pull a wire with a constant velocity, were fabricated and tested. The linear actuator comprised a stepping motor, a ball screw to convert the rotational motion of the motor into linear motion, and a linear guide. It was capable of linear movement for a distance of 120 mm. The deployed stents were simultaneously withdrawn at a speed of 1.0 mm/s. All trials were monitored via an overhanging charge-coupled device video camera (Dino-Lite Digital Microscope AM-2001; AnMo Electronics Corporation, New Taipei City, Taiwan).
Standard and adjunctive techniques
Several adjunctive techniques were compared with several stents as in a previous report: [[2]] a standard deployment, 5-min wait, and the push-and-fluff method.
Results
The results of the machine-guided CCSM with different stent retrievers are shown in [[Table 2]]. For all three stent brands, it was noted that a 5-min wait after deploying the stent was more effective compared with simple deployment with immediate retrieval. Furthermore, the push-and-fluff technique resulted in a higher strength with all retrieval devices.
Table 2: Results of confront clot scrambling method with stent retrievers
Discussion
In this study, the results obtained from the machine-guided CCSM were comparable to those of the conventional method. The manual withdrawal can be affected by operator-specific factors, whereas machine-guided withdrawal led to uniform results. Therefore, the CCSM appeared to be an accurate and reliable technique. In addition, the results showed that the adjunctive push-and-fluff technique resulted in higher strength than the alternatives. Although this technique is an established adjunctive technique for closed-cell stents, the results show that it is also effective with the Solitaire stent, which employs a rolled-sheet design.
In addition, the results of the present study showed that the stent that was deployed first was generally stronger than the one that was deployed after it. On the contrary, the success of the push-and-fluff technique depended on the physician's skill. Therefore, by deploying a stent with the push-and-fluff technique second, the effects of the physician's maneuvering can be effectively confirmed. The degree of stent dilatation could be readily observed by direct visualization. For example, when the pushing force was too strong, the stent tended to bend distally or slip away. Because actual endovascular clot retrieval requires extremely fine maneuvering against internal vessels, repeated training is critical, particularly for beginners. The CCSM can be repeatedly performed; thus, this process can be facilitated at any location or time using low-cost equipment.
In this study, CCSM was not performed in an actual clinical setting, which is one of the limitations of the study. Further investigations are required to confirm our findings and evaluate other vascular models and sham clots. Moreover, a quantitative evaluation is warranted to compare each technique and stent.
Conclusion
The present study aimed to perform one-to-one competitive analyses of stent retrievers during clot capture using CCSM and equitable automatic withdrawal machine. Our results confirm the accuracy and reliability of the CCSM. Although the push-and-fluff technique is the most effective adjunctive technique, it depends on the physician's skill. However, these are preliminary findings in a simulated model with several limitations. The results should be validated by quantitative evaluations to further optimize the stent retrievers and evaluate adjunctive techniques.
