Self-Expanding Stent for Recanalization of Acute Embolic or Dissecting Intracranial Artery Occlusion

Discussion

A recapturable self-expanding stent can be used as either a permanent stent placement or an endovascular temporary bypass method to entrap thrombus against the vessel wall for recanalization in the acute occlusion setting of a major intracranial artery.^4–7 This strategy of using a recapturable self-expanding stent may provide immediate recanalization of an acutely occluded artery. This early restoration of flow may more quickly promote endogenous or pharmacologic thrombolysis. If blood flow through the occlusion site is restored, as seen in patients in this series, the thrombus entrapped by the stent may dissolve due to the GP IIb/IIIa antagonist and/or a small amount of thrombolytics. Furthermore, once reperfusion to the ischemic brain tissue is restored, it allows us enough time to preclude or to minimize the dose of thrombolytics to completely dissolve the remaining entrapped thrombus. A mean of 150,000 U (range, 100,000–300,000 U) of urokinase was used in 8 of 9 patients, which was a very small amount, considering the large amount of thrombus burden at the ICA terminus or proximal MCA. Moreover, in the remaining patient, only GP IIb/IIIa antagonist without thrombolytics was sufficient to prevent reocclusion and to dissolve the entrapped thrombus.

In the cardioembolic occlusion at the ICA terminus, recanalization is very difficult with intra-arterial strategies as well as IV rtPA because of the large amount of thrombus burden. The causes of the 5 ICA terminus occlusions included in our series consisted of 4 cardiogenic embolisms and 1 traumatic dissection. In all 4 cases of cardioembolic occlusion from the ICA terminus extending to both the proximal MCA and ACA, immediate recanalization could be achieved by partial deployment of the stent, despite a large amount of embolus burden. This immediate recanalization may be the most important advantage of the stent placement in acute stroke. Another possible advantage of the stent strategy for recanalization is to prohibit distal migration of the embolus. In our experience, distal migration of the embolus was frequently observed as the embolus dissolved and became smaller during intra-arterial thrombolysis with rtPA or urokinase; one example was the migration of the embolus from the ICA to the MCA. When applying mechanical thrombolysis by using a microwire or balloon, we also frequently observed distal migration/embolization of the embolus or macerated clots. Although the macerated emboli were relatively easily dissolved by thrombolytics or endogenously, it was sometimes problematic in that those emboli frequently occluded the arterial branches supplying the eloquent area of the brain. On the other hand, complete or partial deployment of a self-expanding stent spanning the entire embolus is less likely to cause distal migration or embolization of the embolus. In our patients, there was no distal migration or embolization of the entrapped embolus visible on the angiogram.

One may be concerned that a self-expanding stent may not have sufficient radial force to recanalize the occluded artery. However, initial recanalization was successful in all of our patients, including cardioembolic (n = 7), artery-to-artery embolic (n = 1), and arterial dissection (n = 1). This suggests that a self-expanding stent with low radial force may be sufficient to entrap the embolus against the vessel wall, causing immediate recanalization of acute embolic or dissecting occlusion.

There were only 2 case series regarding the use of self-expanding stents for recanalization in acute stroke in the existing literature, in which recanalization rates with self-expanding stents were 79% and 89%, respectively. ^2,3 In the experimental embolism model, the TIMI 2/3 recanalization rate with self-expanding stents was 91%.⁸ Although it is impossible to directly compare our results and those of the previous 2 case series because of the small number of patients, we guess that the case selection may affect the rate of recanalization. In our patients, the cause of acute arterial occlusion was not arteriosclerotic stenosis but rather obviously emboli or dissection. In the previous 2 series, the causes of acute occlusion were not mentioned; therefore, those cases might have included arteriosclerotic in situ occlusion at the pre-existing stenotic portion of the artery. In our opinion, a self-expanding stent may be less likely to be effective in the recanalization of acute arteriosclerotic in situ occlusion with pre-existing stenosis because of its low radial force.

Recapturability of the Enterprise stent is an important advantage in its use for recanalization of acute strokes. As mentioned in 2 innovative case reports, the recapture of the stent after thrombolysis has several possible advantages over permanent stent placement.^4,5 In our case series, however, recapture was successful in 3 of the 7 attempted cases. One possible explanation is the difference in time from deployment to attempt to recapture between the successful and the failed cases. In the 4 failed cases, the time was ≥120 minutes whereas the duration of our 3 successful procedures and the other 2 reported procedures^4,5 was ≤30 minutes. The longer the stent is partially deployed, the greater is the possibility of microclot deposition within the stent-delivery catheter. This may increase friction and difficulty during the recapture of the stent. In the acute phase of a stroke, 1 of the major concerns regarding the use of the stent is in-stent thrombosis due to the lack of antiplatelet premedication. In our series, in-stent thrombosis occurred in 2 patients, both of whom received only urokinase, not the GP IIb/IIIa antagonist. This suggests that the GP IIb/IIIa antagonist may be essential in stent placement for the recanalization of an acute stroke with lack of antiplatelet premedication. Another major concern is the possibility of increased risk of fatal intracranial hemorrhage associated with procedural and/or postprocedural antiplatelet medication. Although only a small number of patients were included, there was no symptomatic intracranial hemorrhage in our series. The possible risk and efficacy of self-expanding stents for the recanalization of recalcitrant intracranial artery occlusion warrants further study.