Table 1.4–3 Scales used to grade recanalization of an occluded cerebral vessel.
| Thrombolysis in Myocardial Infarction (TIMI): assesses the local vascular findings | |
| TIMI 0 | No recanalization |
| TIMI 1 | Minimal, capillary recanalization |
| TIMI 2 | Partial recanalization |
| TIMI 3 | Vessel is completely patient |
| The Mori scale assesses cerebral perfusion after recanalization of the cerebral vessel | |
| Mori 0 | No perfusion |
| Mori 1 | Minimal reperfusion |
| Mori 2 | Reperfusion area less than 50% |
| Mori 3 | More than 50% reperfusion |
| Mori 4 | Restoration of normal perfusion |
| The Thrombolysis in Cerebral Infarction (TICI) classification represents a combination of TIMI and Mori | |
| TICI 0 | No perfusion, no anterograde flow distal to the occlusion |
| TICI 1 | Capillary flow through the occlusion site, with minimal perfusion and with no contrast in the distal vascular tree |
| TICI 2 | Partial perfusion; the arterial vascular tree distal to the occlusion shows contrast on angiography. However, inflow and/or wash-out are clearly delayed |
| TICI 2a | Only a maximum of two-thirds of the vascular territory after the occlusion is contrasted |
| TICI 2b | The entire vascular territory is contrasted, but with a marked delay as described under 2 |
| TICI 3 | Complete restoration of perfusion with no time delay in the arterial, capillary/parenchymal, and venous phases |
In summary, these three studies show that patients with severe cerebral infarction benefit from local thrombolysis within a time window of 6 hours. In any comparison between the published results on intravenous thrombolysis and those for intra-arterial local thrombolysis, it needs to be taken into account that more severe cases of stroke (NIHSS around 17) were treated with the latter method, while in the intravenous studies strokes with severity grades of 14 (NINDS), 11 (ECASS II) and nine (ECASS III) were treated. The intra-arterial recanalization rates of 66–75% are notable, particularly as they were documented angiographically, with the advantage that the administration of the thrombolytic agent can be stopped once the vessel has become patent, and can checked approximately every 15 minutes by injecting contrast through the guide catheter. Local thrombolysis with a microcatheter, in front of or into the occlusion in the cerebral vessel, thus still represents a simple, relatively low-complication alternative to mechanical recanalization techniques when endovascular access to the occlusion site is difficult due to ectasia, kinking, or stenoses in the cervical vessels, expert interventional experience is lacking, or the diameter of the carotid artery or vertebral artery is too small for devices. The disadvantage is the relatively long time required for recanalization, and for this reason the available dosage (1 million units of urokinase, 0.6 mg rt-PA/kg body weight) is administered using a perfusion system for a period of 90–120 minutes. As the collateral supply to the brain tissue is not impaired by the microcatheter, however, this need not lead to enlargement of the infarction and a decrease in the penumbra provided that blood pressure is kept slightly elevated and stable.
A retrospective meta-analysis including 53 thrombolysis studies reporting recanalization rates within the first 24 hours after the start of symptoms also confirmed the good efficacy of endovascular thrombolysis. According to the data, spontaneous recanalization of an occluded middle cerebral artery occurs in approximately 22% of cases. After intravenous thrombolysis, this percentage can be raised to approximately 50%, while local intra-arterial thrombolysis led to recanalization in 67% of cases (PROACT) and 74% of cases (MELT). If additional mechanical recanalization techniques are used, the occluded cerebral vessel can be reopened in 80–90% of cases. A retrospective comparison of two groups with clinically severe M1 occlusions (NIHSS 17), one of which received intravenous treatment while the other was treated intra-arterially, also showed significantly better clinical results in the group with endovascular treatment. Only 23% of the patients in the IVT arm had good results, in comparison with 53% of those who received endovascular treatment, with “good results” being defined as mRS 0–2 after 3 months. This finding is all the more remarkable in that the IVT was only allowed within a 3-hour time window, so that many stroke patients were excluded from the treatment who could still be treated with intra-arterial thrombolysis within the 6-hour time window.
Sonothrombolysis
The application of ultrasound during thrombolysis is intended to increase its effectiveness, although the precise mechanism involved is not known. In the Clotbust study, 126 patients with MCA occlusions received IVT within the 3-hour time window. The 63 patients in the treatment arm also received continuous transcranial ultrasound at 2 MHz during the infusion of the thrombolytic agent. Complete recanalization (TIMI 3) was significantly more frequent in the treatment arm (46% vs. 18%; P < 0.001). By contrast, the rate of symptomatic intracranial hemorrhage, the mortality rate, and the final clinical results did not differ significantly.
Another study, in which transcranial ultrasound (300 kHz) was used to supplement IVT within a time window of up to 6 hours, had to be stopped prematurely because symptomatic intracranial bleeding occurred in five of the 14 patients (36%) in the treatment arm. In the Interventional Management of Stroke (IMS II) study, a combination of IVT/IAT and endovascular ultrasound applied using a 3.3F catheter led to complete recanalization in 69% of cases after a treatment period of 2 hours. However, six of the 33 patients (18%) suffered symptomatic intracranial hemorrhage. The catheter is only suitable for the treatment of large arteries (up to the M2 segment) and could not be advanced intracranially through an extremely tortuous internal carotid artery (ICA) in 9% of the patients.
Aspiration (Figs. 1.4-20, 1.4-21)
Recanalization by aspirating the thromboembolic foreign material for endovascular treatment of acute stroke is a particularly attractive method for several reasons:
