Aneurysmal subarachnoid hemorrhage (aSAH) contributes disproportionately to stroke-related disability due to its prevalence in younger patients. Large vessel vasospasm complicates aSAH and is often treated with endovascular rescue therapy (ERT). However, clinical trials have not demonstrated a clear link between vasospasm improvement and better outcomes. We hypothesized that improving vessel caliber alone may not ensure better blood flow to brain parenchyma, and we studied how vessel caliber relates to perfusion in the context of ERT. We measured the internal carotid artery (ICA) caliber and time to maximum of the residual function (Tmax) from digital subtraction angiography (DSA) before and after ERT in 150 vessels from 36 patients. ERT increased ICA caliber (Δ1.13 ± 3.8 mm2, p < 0.01) and accelerated mean Tmax (Δ-215 ± 483 ms, p < 0.01). The percent change in ICA caliber with ERT was weakly correlated with the change in Tmax (R2 = 0.04, p < 0.01). In contrast, Tmax before ERT strongly predicted Tmax after ERT (R2 = 0.62, p < 0.01) in both univariate and multivariable models. We conclude that a perfusion metric (Tmax) is superior to vessel caliber in predicting the response to ERT. Validating these findings may shift the clinical focus from vessel caliber to perfusion metrics when evaluating vasospasm and aSAH outcomes.
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