Danielle de Sa Boasquevisque, MD
Patients with basilar artery occlusion (BAO) comprise 10-20% of all large vessel occlusion cases but carry high mortality and morbidity rates, reaching up to 95% if recanalization is not achieved. The optimal approach for treatment of this life-threatening condition – including the optimal time-window – is still heavily debated. Mechanical thrombectomy is currently the standard of care for this population in most stroke centers, despite the lack of evidence compared to anterior circulation.
Studies up until now showed that some factors are related to better recanalization rates in this population and hence, better prognosis. These variables were hyperdense basilar artery, short thrombus length, early initiation of endovascular therapy and contact aspiration. Some case-reports have also suggested that anatomic and hemodynamic factors related to reversal flow and patency of vertebral arteries could affect recanalization success.
The primary objective of this study by Boeckh-Behrens et al. was to to investigate the association between low flow condition contralateral to the catheter-bearing vertebral artery and successful recanalization post-mechanical thrombectomy (MT) in a population individuals with acute basilar artery occlusion. The authors hypothesized that patients with low flow condition defined as either aplastic or hypoplastic vertebral artery (< 50% of the dominant artery) contralateral to the catheter position have more chances to achieve complete recanalization once they have less risk of distal emboli.
All patients were subjected to digital subtraction angiography. The complete vertebrobasilar axis recanalization was defined as grade 9 (on a scale of 1 to 9), and it could be achieved with or without residual branch occlusion.
This study included 115 patients who underwent MT with the following indications: any relevant acute neurological deficit, occlusion of the vertebral, and basilar or posterior cerebral arteries (involving the P1-segment) on computed tomography angiography. In terms of MT techniques, direct contact aspiration was usually attempted first, followed by stent-retirever after at least 3 failed aspiration attempts. Stand-alone aspiration was used in 21 patients (18.3%), 67 (58.3%) were treated with stent-retrievers only, and another 21 patients (18.3%) were treated with a combination of both. Complete vertebrobasilar axis recanalization (grade 9) was achieved in 92 of the 115 (80%) patients.
The primary outcome was defined as a modified Rankin Scale (mRS) score of 0 to 3. Secondary outcomes were rates of mRS score of 0 to 1, mRS score of 0 to 2, substantial neurological improvement and mRS shift analysis. Other safety outcomes included any type of hemorrhagic transformation, symptomatic intracerebral hemorrhage, subarachnoid hemorrhage, and in-hospital mortality.
They found that successful recanalization was more frequently showed in patients under the contralateral low flow condition. This association was present across all distal aspiration catheter positions used (common OR: 3.95; 95%CI, 1.64-9.49). In the multivariable logistic regression analysis, independent factors associated with complete recanalization were intravenous tPA, number of occluded segments (inversely related) and contralateral low flow conditions.
The results presented showed that when intention to perform aspiration was considered in patients with contralateral low flow conditions, stand-alone aspiration was often more successful than a combined approach with stent retrievers. The number of passes required was less in patients with low flow compared with those with normal or high flow. Patients with complete posterior recanalization also tended to have higher mRS scores. Complete recanalization remained strongly associated with mRS after adjusting for relevant confounding variables, regardless of whether collateral grading was included or not. In-hospital mortality was also lower in patients with complete recanalization, while rates of symptomatic hemorrhage, hemorrhagic transformations and subarachnoid hemorrhage did not differ between groups.
In conclusion, patients with low collateral flow achieved higher rate of complete recanalization. The clinical impact of complete recanalization reflects less distal emboli and is measured by the modified Rankin Scale. It would be interesting to address how we can modulate the contralateral flow during the endovascular procedure or if there is benefit in using ipsilateral balloon guide catheter during the procedure for patients with contralateral normal or high flow, for instance, those with bilaterally patent vertebral arteries.
