Aspiration techniques are mainly used to recanalize occlusions in the large vessels supplying the brain. Aspiration catheters with gauges of 5F and 6F are now available with a highly flexible distal third and with a curve at the tip that is preformed or can be shaped using steam or hot air. As they have a hydrophilic coating and reinforced proximal catheter shaft, they can be advanced using a telescoping technique through a 7F or preferably 8F catheter, sometimes without wire guidance, to occlusion sites in the M1 segment of the middle cerebral artery, or into the basilar artery. The siphon in the internal carotid artery usually offers the greatest resistance, as it is attached to bone and hard meninges and cannot be stretched. The tip of the aspiration catheter is advanced to the proximal end of the thrombus under imaging guidance (road map). As soon as the occlusion has been reached and blood stops flowing back through the aspiration catheter, a lockable 50-mL aspiration syringe is used to attach the thrombus to the tip of the aspiration catheter. The negative pressure that can be created with this technique at the tip of a 5F aspiration catheter is approximately 10 times greater than the suction pressure created by the Penumbra pump (see below), and it usually leads to deformation and fixation of the thrombus at the tip of the aspiration catheter. After approximately 1–2 minutes, with negative pressure being maintained and proximal flow arrest, the aspiration catheter is withdrawn. If spontaneous return flow from the guide catheter is not observed during this withdrawal maneuver, then it also has to be carefully aspirated; irrigation of the guide catheter must cease during this maneuver.
Fig. 1.4–20a-g Technique for revascularization of an acutely occluded internal carotid artery (T occlusion) in a 70-year-old patient with aphasia and right-sided hemiplegia (NIHSS 19). (a) The first-pass contrast magnetic resonance angiogram shows the occluded internal carotid artery on the left. (b) Common carotid angiogram on the left, with the stump of the left internal carotid artery. (c) The occlusion is passed with a long (3 m) 0.038” wire using a biplanar road map. (d) Passage with a 5F aspiration catheter and the 8F guide catheter during continuous aspiration. (e) Stenting, with distal protection provided by a filter-wire protection system. (f) Checking with 3D rotation angiography after aspiration and stent placement. (g) The thrombus aspirated using the 8F catheter.
The disadvantage of this technique is that the withdrawal of the aspiration catheter causes loss of access, and the segment from the tip of the guide catheter up to the occlusion has to be traversed again if the thrombus cannot be removed on the first attempt.
The Penumbra system (Fig. 1.4-22) consists of an aspiration catheter that is navigated to the front of the vascular occlusion, with an aspiration pump that ensures continuous aspiration of the thrombus, which is simultaneously fragmented inside and outside the catheter tip by a wire with an olive-shaped tip. This means that the thrombus can be suctioned out piece by piece, with the aspiration catheter being kept clear. Despite higher recanalization rates of over 80%—which have usually been achieved in combination with administration of thrombolytic agents in bridging therapy—the clinical results are not satisfactory in all cases. This is because on the one hand, the negative pressure created by the pump is relatively low, while on the other the fragmentation movement of the separator takes place outside of the aspiration catheter and thus in an area that is not visualized angiographically and/or by the road map. Although the separator wire is relatively soft, vascular injury, dissection, or spasm can occur quite rapidly if the tip of the aspiration catheter is directed at the vascular wall while passing a curve, so that the separator has no space available, or if the occlusion (as is often the case) is located in a vascular bifurcation towards which the tip of the aspiration catheter is directed. In addition, if there are small perforating branches that originate immediately in front of or inside the occlusion, thrombus fragments may be pressed by the separator itself into still-patent branches beyond the bifurcation, or may be washed back into reopened side branches during the recanalization procedure. The aspiration catheters supplied by Penumbra also had relatively small lumens, although there is now a 5F system recently added.
Fig. 1.4–21a-c Acute occlusion of the internal carotid artery after heart surgery. (a) Lateral digital subtraction angiography image of the internal carotid artery. (b) The recanalized internal carotid artery after aspiration. (c) Deformation of the thrombus due to forced aspiration through the 5F aspiration catheter.
Fig. 1.4–22a, b The Penumbra aspiration system, with microcatheters in various sizes, corresponding separators, and the aspiration system. The thrombus is broken up by advancing and withdrawing the separator, and the fragments are continuously aspirated.
Mechanical retriever systems
Since 2000, there have been increasing numbers of publications describing small series and case reports of successful recanalization of cerebral vessels using microinstruments that were initially developed to manage complications during endovascular procedures. In individual cases, the grasping instruments developed for the purpose (such as microsnares and micro-alligator clips) can be used to grasp compact thrombi and remove them from the vessel. Numerous mechanical thrombectomy systems have been developed on the basis of this experience.
The retriever systems act at the distal end of the occlusion. It is therefore necessary to pass the occlusion site with a microwire and microcatheter, so that on the one hand there is a risk of vascular perforation and on the other a possibility of further distal migration of the thrombus. As a result these systems are increasingly being used in combination with proximal protection devices, and the following procedure is recommended for M1 occlusions: