Alrohimi and colleagues reported that in patients with acute ischemic stroke due to large vessel occlusion transferred from a primary stroke center (PSC) to a comprehensive stroke center (CSC) for endovascular therapy (EVT), Alberta Stroke Program Early CT Score (ASPECTS) decay, defined as a ≥2-point decrease in ASPECTS from PSC to CSC, occurred in 36% of cases. Poor baseline collateral score was associated with ASPECTS decay, which in turn was linked to shorter 90-day home time. ^{Reference Alrohimi, Ishaque and Wagner1} Importantly, this study used prospectively acquired provincial registry data linked to the healthcare system, lending robustness to its findings.

This work highlights the importance of collateral assessment at the PSC to predict ASPECTS decay. However, the optimal advanced imaging strategy for PSCs remains under debate. ^{Reference Campbell2} In this study, collateral status was assessed using single-phase CT angiography (CTA), and 41% of patients were excluded from EVT mainly because of ASPECTS decay. These findings highlight the potential role of multimodal CT stroke imaging in PSCs to reduce inappropriate transfers. ^{Reference Goyal, Menon and Wilson3} The work also highlights the use of home time as a practical/administrative data-derived and validated outcome, perfect for assessing quality of care provincially. ASPECTS decay from long transport times (median transfer time of 250 minutes between hospitals) was strongly associated with poor outcomes. Careful decision-making is needed in this population, assessing baseline imaging such as poor collaterals. Finally, as the authors noted, future clinical trials of neuroprotective strategies can aim at mitigating ASPECTS decay and may serve as a practical and relevant surrogate outcome for such trials.

Several questions remain. Would multiphase CTA (mCTA), ^{Reference Menon, d’Esterre and Qazi4} becoming available across Canada, provide more reliable collateral assessment and improve prediction of ASPECTS decay at PSCs? Sometimes, the image acquisition of single-phase CTA is too early to visualize late leptomeningeal filling, misinterpreted as collateral absence. The mCTA offers detection of delayed collateral filling only requiring multiple movements of the CT gantry and modest additional radiation exposure, which does not add substantial costs for PSCs in the Canadian Health Care system context. Given that the study period was from 2015 to 2020, how might the increasing use of Tenecteplase since 2020 affect ASPECTS decay? Very early reperfusion is crucial in stroke patients with rapidly expanding infarcts. The Canadian AcT trial demonstrated a trend toward better outcomes with Tenecteplase over alteplase in the subgroup enrolled at PSCs. ^{Reference Menon, Buck and Singh5} This is likely due to higher rates of early reperfusion as shown by Yogendrakumar, et al. ^{Reference Yogendrakumar, Beharry and Churilov6}