1.4.5.4 Stent retriever device (Figs. 1.4-27, 1.4-28)
Initial attempts to achieve rapid, albeit transient, recanalization without definitive placement of a stent was accomplished by not fully releasing the self-expanding stent, so it could be withdrawn again into its sheath and retrieved when desired. The Solitaire stent (Covidien, ev3 Endovascular Inc., Plymouth, Minnesota, USA), which was originally developed for stent protection in endovascular treatment of broad-based aneurysms, proved to be particularly suitable. This is a laser-cut self-expanding stent that is attached to a guide wire with which it can be introduced and removed again through a 0.0021-inch microcatheter (Rebar, Prowler). As with coils for aneurysm treatment, the stent can be released from the wire electrolytically and can remain in place. The stents are available with various lengths and diameters, from 4 × 15 mm to 6 × 30 mm. When the stent is withdrawn in its opened state after approximately 5 minutes, animal experiments and small case series have shown that the thrombus is also removed in the stent mesh and that this leads to rapid recanalization of the vessel in around 90% of cases. Although the stent is withdrawn in its expanded state, spasm occurs rarely and dissections very rarely.
If possible, withdrawal of the stent retriever should be carried out in flow arrest through a large-lumen (8 or 9F) balloon guide catheter that is “parked” in the distal internal carotid artery and briefly opened during withdrawal of the stent.
Prospective single-center and multicenter registry studies have confirmed that using the stent retriever significantly reduces the time required for the intervention and achieves recanalization rates of 80–90%. This is paralleled by a marked improvement in the clinical results: 121 patients with acute stroke (NIHSS 18) were treated within the first 6 hours using the Solitaire retriever system in five centers in Europe. The recanalization rate was 90%, and 55% of the patients had good clinical results after 3 months, defined as mRS 0–2. This is much better than the results in the intravenous thrombolysis studies, although the latter only treated patients within a time window of 3–4.5 hours and only included patients with significantly milder cases of stroke with NIHSS scores of between 9 and 16.
Stent retriever systems are now being supplied by various companies, each with a slightly different design.
1.4.5.5 Combined intravenous thrombolysis and endovascular treatment (bridging approach)
This combined treatment approach is increasingly being used in stroke networks. In smaller hospitals, cerebral bleeding can be excluded as the cause of stroke using computed tomography, which is widely available, and intravenous thrombolysis can be started without delay. While this treatment is already taking effect, the patient can be moved to a center in which the technical facilities are then available for carrying out endovascular treatment if there is no improvement with the intravenous thrombolysis. If the patient’s condition has changed on admission to the center, and/or more than 1–2 hours has passed, the center should carry out further imaging diagnosis in order to exclude bleeding into the infarct, or in any event to document successful recanalization using the intravenous bridging thrombolysis.
Fig. 1.4–27a, b (a) A retrievable stent. (b) Documentation of the thrombus in the stent after recanalization of a thromboembolic occlusion of the middle cerebral artery.
Fig. 1.4–28a-d Acute stroke in a self-sufficient 89-year-old who called the emergency physician herself (NIHSS 19). (a) Occlusion of the right middle cerebral artery. (b) Immediate capillary recanalization after initial deployment of the retrievable stent. (c) Detailed angiography (spatial resolution 0.1 mm) of the reopened capillary lumen after compression of the thrombus onto the wall by the stent, which is still in place. (d) Complete recanalization after removal of the stent. The patient wanted to go home again the next day to look after her husband and cat.
Studies on combined intravenous/intra-arterial thrombolysis have used lower intravenous dosages (0.6 mg rt-PA/kg body weight) in order to complete the intra-arterial thrombolysis with the remaining dose of rt-PA or urokinase. It also appears acceptable to administer the full dosage of rt-PA, 0.9 mg/kg body weight, followed by endovascular treatment if recanalization does not take place, as endovascular treatment is increasingly limited to the use of mechanical recanalization techniques.
1.4.5.6 Multimodal endovascular therapy
Modern approaches to the treatment of acute stroke take into account both the location of the occlusion and also the time between the start of symptoms and the therapeutic intervention. The treatment of vertebrobasilar infarctions begins with IVT within a 4.5-hour time window. The patients should be transferred without delay to a center in which mechanical recanalization can follow if needed. If the patient has in the meantime become comatose and is showing more extensive clinical symptoms of a brainstem lesion, multimodal magnetic resonance diagnosis should be carried out first in order to allow interdisciplinary assessment of the prognosis—e.g., imminent “locked-in” syndrome—and discussion of it with relatives.
Patients with an infarct in the carotid territory should receive IVT if they are within the 4.5-hour time window and there is no occlusion of the ICA or M1/M2 segment. For patients in whom the 4.5-hour window has already been exceeded, or who present with a larger vascular occlusion (ICA, M1, and M2), endovascular therapy is prepared, with or without bridging therapy, the time window for which is 6 hours for the middle cerebral artery. The endovascular procedure is carried out with anesthesia facilities on hand, through a wide-lumen port (8F), which keeps all options open for the subsequent procedure. After diagnostic imaging of both carotid territories and the posterior circulation, a 7F or 8F guide catheter is positioned in the relevant cervical artery. If there is a combined ICA/ MCA occlusion, the ICA is initially recanalized using aspiration via the 8F catheter, with stent placement if needed. This improves perfusion of the collaterals and prevents re-occlusion. If the MCA is not already recanalized by the aspiration at this point, we follow this with IAT (< 6 h) or thromboembolectomy (< 8 h).
Depending on how much time has passed and upstream ICA conditions, occlusions of the MCA can initially be treated with IAT or aspiration (with a 4–5F catheter). IAT is carried out via a 2.4F microcatheter, the tip of which is placed in the thrombus. We infuse no more than 1 million IU urokinase via an infusion pump that distributes the dosage over a period of 90–120 minutes, with angiography being carried out via the guide catheter after 30 minutes and then every 15 minutes. The intra-arterial thrombolysis is then stopped once recanalization occurs. This makes it possible to reduce the rate of symptomatic intracerebral bleeding to less than 5%. Thrombolysis can be speeded up with careful passage and manipulation of the thrombus with the microwire and microcatheter. However, the risk of vascular perforation needs to be considered in all forms of manipulation. With persistent occlusions, or when IAT is contraindicated, mechanical procedures can be used for thrombectomy, PTA, and/or implantation of a stent as the last resort. The introduction of retrievable stents has changed the situation such that this technique can now be used as a primary form of endovascular therapy, with or without intravenous bridging treatment, since recanalization can be achieved rapidly and safely in a very high percentage of cases.
References
Alexandrov AV, Molina CA, Grotta JC, et al. Ultrasound-enhanced systemic thrombolysis for acute ischemic stroke. N Engl J Med 2004; 351: 2170–8.
Arnold M, Schroth G, Nedeltchev K, et al. Intra-arterial thrombolysis in 100 patients with acute stroke due to middle