The first cases series on FAST was published in 2011 under the title, “Direct thrombus retrieval using the reperfusion catheter of the Penumbra system: Forced-suction thrombectomy in acute ischemic stroke” [6]. In that case series, 22 consecutive patients with large artery occlusion acute ischemic stroke within the 8 h time window of stroke onset underwent FAST. Any patients that were at high risk of bleeding, or had brain edema, or uncontrolled hypertension, were excluded. The safety of the technique was evaluated according to the incidence of procedural complications, and the efficacy was assessed by the incidence of successful revascularization of the target vessel following the technique, defined as Thrombolysis in Cerebral Ischemia (TICI) grade 2 or 3. The mean interval from the onset of symptoms to arterial puncture was 5.3 h, and the mean baseline NIHSS score was 18.1. The target-vessel locations were 14 middle cerebral artery (MCA) (63.6%), 4 ICA (18.2%), and 4 BA occlusions (18.2%). All the treated target vessels were TICI 0 before the procedure; and all 81.9% of the patients were successfully recanalized as TICI 2b (10/22, 45.5%) or 3 (8/22, 36.4%) after the FAST procedures. The mean procedure time from groin puncture to revascularization was 40.2 min, including diagnostic angiographies. A Penumbra reperfusion catheter 041, the original version of the catheter, was primarily used in every patient and a Penumbra reperfusion catheter 032 was additionally used in two cases of distal embolization to the M2 segment of the MCA. Adjuvant procedures were performed in four patients; balloon angioplasty was undertaken in one patient due to the underlying stenosis of the BA following revascularization of acute BA occlusion, and rescue carotid stenting at proximal ICA was performed in three patients. And there was only one procedural complication, cervical segment ICA dissection occurred while placing the guide catheter in the tortuous vessel, although recovery was confirmed on follow-up MR angiography 5 days after the procedure. Overall intracerebral hemorrhage (ICH) occurred in seven patients (31.8%) and among them, two (9.1%) were symptomatic. The favorable functional outcome (mRS score 0–2) at 3 months was 45.5% (10 of 22 cases).

One year later, the authors of the first FAST paper reported the efficacy of FAST in acute distal ICA occlusions by comparing FAST and MCD and showed greater improvement in functional outcome in the FAST group [8]. In that period-to-period analysis, the rate of successful recanalization, defined as TICI grade 2 or 3, was significantly higher in the FAST group compared to the mechanical clot disruption (MCD) group (85% vs. 32%, P < 0.001). Additionally, favorable outcomes at 3 months, defined as mRS score 0–2, were 45% in the FAST group and 16% in the MCD group. Though this was a comparison between a new technique FAST and an outdated MCD at the time, the authors concluded FAST could be a viable option for acute distal ICA occlusion based on the high rate of successful recanalization and functional recovery.

In 2013, another investigation of manual aspiration thrombectomy, with the modification of the standard Penumbra system, took place called ADAPT [7]. In that study, 37 consecutive cases of acute ischemic stroke were treated with the ADAPT technique, 30 of which involved the anterior circulation, seven involving the posterior. The ADAPT, as discussed in that publication, was very similar to the FAST technique (Fig. 10.2). Regarding the specific findings of ADAPT study in 2013, the average time from groin puncture to recanalization was 28 min, and revascularization was successful in all cases. TICI grade 3 recanalization was achieved in 65% of the cases. Patients presented with an admitting NIHSS score of 16.3, and improved to 4.2 by the time of discharge. In that study, there was one procedural complication. And two patients died from parenchymal hematomas.

The authors of the ADAPT study pointed out some differences between the early FAST technique and ADAPT. For example, they indicated that the FAST series reported more modest results than their ADAPT results likely due to smaller caliber and older technology aspiration catheters. In detail, they indicated that the FAST series involved an older generation aspiration catheter, such as 041 and 032 family of Penumbra reperfusion catheters, as opposed to their more modern devices (Penumbra 5 Max) used 2 years after the FAST study. They mentioned two major advantages of using the new aspiration catheter for ADAPT: (1) the increased internal diameter of the Penumbra 5 Max aspiration catheter allowed for an increased surface area, which provided better contact at the catheter tip-thrombus interface, and (2), additionally, the Penumbra 5 Max was more spacious in its proximal segment, which increased its luminal volume and provided an increased aspiration capacity.

The techniques of early FAST and ADAPT were very similar in many ways; both techniques were mainly composed of advancement of large-bore catheter to the occlusion site and a forceful aspiration thereafter. From the FAST author’s viewpoint, it was with the additional use of a BGC in subsequent years that set FAST slightly apart from ADAPT. The only possible disadvantage of using a BGC is the time for preparation of a balloon in BGC. But there are several potential advantages here.

The first advantage is that using BGC in the FAST procedure may minimize distal clot migration or embolization. For example, in an in vitro study published in 2013, the incidence of distal embolization was investigated [9]. In that study, the Merci retriever, Solitaire FR (Medtronic Neurovascular, CA, USA), and Trevo devices (Stryker Neurovascular, CA, USA) were compared with and without the use of a BGC to ascertain the number of distal emboli generated during thrombus retrieval. They found that the use of the BGC during thrombus retrieval significantly reduced the formation of large distal emboli with a diameter >1 mm, regardless of the device used (P < 0.01). Additionally, they found that applying aspiration using the BGC in place of a conventional guide catheter resulted in a significant increase of flow reversal (P < 0.0001). The findings related to be reduced embolic events with use of a BGC have also been demonstrated in animal models [10]. In an experimental ischemic stroke model, the number of embolic events was significantly higher with distal thrombectomy device, such as Catch retriever (Balt Extrusion, Montmorency, France), without proximal balloon occlusion compared with use of distal devices with proximal balloon occlusion (42% vs. 9%, OR, 7.1; 95% CI). That brings up the second potential advantage. It may be the case that using a BGC might enhance aspiration efficacy during the FAST or ADAPT procedure by blocking proximal flow. Note that this is a theoretical point; there is no apparently reported evidence to confirm this conjecture yet. However, because the distal part is already blocked by the clot, proximal occlusion with a BGC can make a vacuum there, which then may make the negative pressure more effective. Clearly, this is an area where in vitro confirmation is needed. The third advantage is that it can allow for easy and prompt switching to stent retriever technique in case of failure using the FAST. This may be an important point, especially in light of modern trials, because all the large volume stent retriever trials recommend using the BGC, for example, Solitaire with the intention for thrombectomy (SWIFT) and Solitaire with the intention for thrombectomy as primary endovascular treatment for acute ischemic stroke (SWIFT PRIME) [11, 12]. Regarding the use of the BGC in stent retriever technique, there was a swine model testing the Solitaire device [13], which noted that the clot would be engaged within the struts and would shear off the device during retrieval into the tip of the BGC in many cases. It was possible to aspirate the clot into the guide catheter and prevent distal emboli. Another study published in 2014, which examined the safety and efficacy of the BGC, demonstrated that the use of a BGC with the Solitaire FR device resulted in better revascularization results, faster procedure times, and improved clinical outcomes [14]. In that study, 149 patients (44%) had placement of a BGC. What they found was that procedure time was shorter in patients where the BGC was used (120 vs. 161 min, P = 0.02), and TICI 3 reperfusion scores were higher in patients with the BGC (53.7% vs. 32.5%, P < 0.001). Although rates of distal embolization and emboli in new territory were similar between the two groups, mean discharge NIHSS score (12 vs. 17.5, P = 0.002) and good clinical outcome at 3 months were significantly better in patients where the BGC was used compared with patients without (51.6% vs. 35.8%, P = 0.02). Additionally, it was shown in multivariate analysis that the use of the BGC was an independent predictor of good clinical outcome (OR, 2.5; 95% CI).

Despite recent huge advances in the large-bore aspiration catheter’s tracking facility, crossing the curved segment of cerebral arteries, such as the carotid siphon, is still not always easy. Tortuosity itself is one big barrier for passage, and the anatomic condition where a small artery is arising from the tortuous segment, such as an ophthalmic artery origin from the carotid siphon, can be another challenging situation during advancement (Fig. 10.4a). Moreover, underlying atherosclerotic stenosis is another potential barrier for catheter passage by making the endothelial surface uneven and rough. In this section, a few technical tips to overcome such obstacles will be introduced.

There are two major mechanical thrombectomy techniques that have emerged as the dominant strategies in the present era of endovascular stroke therapy. The primary involves the use of a stent retriever, such as the Solitaire FR (Medtronic Neurovascular) or the Trevo device (Stryker Neurovascular). The second type of technique is the use of direct clot aspiration, using either the FAST or the ADAPT techniques with a large-bore aspiration catheter, such as the Penumbra 5 Max or 5 Max Ace (Penumbra). In addition, there have been a few attempts to enhance the rate of successful recanalization through a combination of the two major techniques, stent retriever and direct clot aspiration. The background of such attempts is straightforward. Despite advancement of the devices and techniques, 100% successful recanalization cannot be guaranteed solely using a primary mechanical thrombectomy, whether the stent retriever or clot aspiration is adopted as the primary technique. In the cases of a stent retriever being used as the primary device, the rate of successful recanalization was 83% in the SWIFT trial (TIMI 2–3: 45/54) and 85% in the TREVO 2 trial (TICI 2–3: 73/86) [11, 17]. Even in the more recent randomized controlled trials of 2015, which were mostly based on stent retriever thrombectomy, the rate of successful recanalization defined as TICI 2b or 3 was 59% in Multicenter Randomized CLinical trial of Endovascular treatment for Acute ischemic stroke in the Netherlands (MR CLEAN; 82% of the device used was stent retriever), 86% in EXtending the time for Thrombolysis in Emergency Neurological Deficits with Intra-Arterial therapy (EXTEND-IA; only Solitaire FR is used), 72% in Endovascular treatment for Small Core and Anterior circulation Proximal occlusion with Emphasis on minimizing CT to recanalization times (ESCAPE; 79% of the device used was stent retriever and 61% was Solitaire FR), 88% in SWIFT PRIME (only Solitaire FR used), and 66% in Revascularization with Solitaire Device Versus Best Medical Therapy in Anterior Circulation Stroke Within 8 h (REVASCAT; only Solitaire FR used) [12, 18–21]. Although the detail of the interventional strategy was slightly different in each trial, these findings apparently demonstrate that practitioners were required to prepare adjuvant rescue procedures for the patients without successful recanalization through the primary devices. Similar findings were reported regarding the use of clot aspiration as the primary technique. The rate of successful recanalization defined as TICI 2b or 3 was 82% in the first FAST trial, 65% in the next FAST trial for acute ICA occlusions, and 75% in the ADAPT trial [6–8]. Likewise with stent retriever thrombectomy methodology, if clot aspiration with a large-bore catheter is adopted as the first-line technique, the practitioner may need to employ potential salvage with a stent retriever or another treatment, if several passes fail to achieve successful recanalization or if advancement of the large-bore aspiration catheter to the occlusion site fails by the vascular tortuosity.

Based on the aforementioned background, there have been a few attempts to improve recanalization by using the stent retriever and clot aspiration together. The first was called the “switching strategy,” which involved switching from FAST to Solitaire stent thrombectomy and the second is the “Solumbra technique,” which uses the two devices simultaneously [22–26]. Although both attempts bear similarities in terms of the concept of combined usage of two major techniques, the detail is very different. Some of the difference lies in the regulatory rules and laws prevailing in the originating countries. For example, the switching strategy of mechanical thrombectomy actually originated as a result of a limitation in the health insurance system in South Korea. Specifically, the public health insurance system supported by government in South Korea pays for about 90% of the price of the first device, either a stent retriever or a large-bore aspiration catheter during the mechanical thrombectomy for a major stroke patient. This means that if the practitioner used a second device for rescue, the patient’s family pays fully for the second device. Therefore, the practitioners under such health insurance system naturally try their best to achieve successful recanalization by using only one device and then “switch” to a second device as a rescue procedure. On the other hand, in some other countries such as the USA, practitioners are allowed to simultaneously use both the stent retriever and the large-bore aspiration catheter at once under the practitioner’s discretion during the procedure, so some practitioners routinely use both devices to enhance the rate of successful recanalization. The most common combination is to use the Solitaire FR stent (Medtronic Neurovascular) and the Penumbra reperfusion catheter (Penumbra), so this has come to be known as the “Solumbra technique.” The details of both the switching strategy and the Solumbra technique will be discussed in the following.