A patient with basilar artery occlusion (BAO) stroke is brought to a hospital and the frantic family at bedside asks what can be done to help their loved one. This unfortunate scenario is a frequent moment of dread to most providers as the best treatment option in a BAO stroke is still uncertain. In this section, we will highlight Endovascular Therapy for Stroke Due to Basilar-Artery Occlusion (BASICS)1 trial which was designed to investigate whether endovascular therapy (EVT) is beneficial as opposed to standard medical care in a BAO stroke.
The Basilar Artery International Cooperation (BASICS) study was published in the New England Journal of Medicine in May 2021. This was a multicenter, international, open-labeled, blinded, randomized control trial in 23 centers in 7 countries from 2011 to 2019. This study examined EVT vs standard medical care and was initially designed to include BAO stroke patients from the age of 18-85 with NIHSS of 10 or more who were within 6 hours of occlusion onset without contraindications to IVT and without evidence of extensive bilateral brainstem infarction, cerebellar mass effect or acute hydrocephalus. The primary efficacy outcome was a favorable functional outcome defined as a mRS of 0-3 at 90 days and the primary safety endpoints were SICH within 3 days of treatment and 90-day mortality rates.
David R. Landzberg, MD
Alhamza R. Al-Bayati, MD
On initial design, a required sample size of 750 patients was determined. Due to slow enrollment, 4 years into the trial and after 91 patients were randomized, the inclusion criteria were expanded to include patients that were 85 years of age or older, those who had a NIHSS of less than 10 and those who had contraindications to IVT. Also, after publication of further trials on EVT of anterior circulation LVO, the anticipated favorable outcome was increased resulting in a decrease of the required sample size to 300 patients. Four hundred and twenty-four patients were eligible however, only 300 were enrolled (154 patients were assigned to EVT and 146 patients to medical treatment). Among the 124 eligible patients who received treatment outside the trial, 98 (79.0%) underwent EVT. Three patients in the EVT group and seven patients in the medical group crossed over into the opposite group.
No statistical significance was found in the primary outcome between the intervention and medical therapy groups. The EVT group had 44.2% of patients with a good functional outcome as compared to 37.7% in the medical therapy group (risk ratio 1.18; 95% CI 0.92-1.50; P=0.19). There was no significant difference in the primary safety outcomes of mortality at 90 days (38.3% in EVT group and 38.3% in the medical care group; risk ratio 0.87; 95% CI 0.68-1.12) and SICH (4.5% in the EVT group and 0.7% in the medical care group; risk ratio 6.9; 95% CI 0.9-53.0).
The good functional outcome percentage in the medical therapy group was much higher than expected, as well as higher than what had been seen in the BEST study (38% in BASICS compared to 32% in BEST). Due to the shorter treatment window of 6 hours from occlusion onset (as compared to 8 hours in BEST) as well as initial design excluding patients with contraindications to IVT, there was a much greater rate of IVT in the BASICS trial (76.7% in BASICS control group vs 32% in BEST control group). The higher percentage of good functional outcome percentage in BASICS medical therapy group is potentially explained by the high rates of IVT as well as the possibility that IVT is more successful in BAO than anterior proximal artery occlusions.
While there was a difference of 6.5% between the prevalence of favorable outcomes in the two groups, this could have been considered significant if the original power calculation estimates of a 10 %-point difference was kept without redesigning the trial to be powered for a speculated 16%-point difference between the intervention and control group. This highlights the fact that this trial could not have had a large enough sample size to detect a statistically significant difference between the two groups. The lack of equipoise among stroke centers worldwide could explain the slow recruitment and the subsequent need to redesign of the trial. This is, in part, due to the ethical challenges of randomizing patients to non- EVT in the setting of overwhelming benefit of EVT in anterior circulation strokes and well-established poor outcomes if left unoffered. Lastly, selection bias likely factored in among this cohort given the large percentage of eligible patient who underwent EVT instead of getting enrolled in the study.
In summary, caution is needed in interpreting these primary analysis conclusions given the severe limitations that are inherent in BAO stroke trials. Many questions remain unsettled, especially with the BEST trial showing superiority of EVT in the per-treatment and as-treated secondary analysis as well as the higher rates of favorable outcomes than expected in the medical therapy group in the BASICS trial. Future trials, such as The Basilar Artery Occlusion Chinese Endovascular (BAOCHE) study that is still ongoing could potentially shed further light and guidance. In the meantime, the decision for EVT in BAO strokes should be an individualized treatment decision factoring in patients’ clinical presentation, vascular anatomy, and ability to receive IVT.
Langezaal LCM, van der Hoeven E, Mont’Alverne FJA, et al. Endovascular Therapy for Stroke Due to Basilar-Artery Occlusion. N Engl J Med 2021;384:1910-20.
Schonewille WJ, Wijman CA, Michel P, et al. Treatment and outcomes of acute basilar artery occlusion in the Basilar Artery International Cooperation Study (BASICS): a prospective registry study. Lancet Neurol 2009; 8: 724–30.
Mattle HP, Arnold M, Lindsberg PJ, Schonewille WJ, Schroth G. Basilar artery occlusion. Lancet Neurol 2011; 10: 1002–14.