Discussion

We found that 41% of patients with acute ischemic stroke and LVO within 24 hours of last seen normal time underwent EVT after evaluation at a comprehensive stroke center. While the clinical characteristics and outcomes in patients undergoing EVT have been previously extensively studied, ^{Reference Mulder, Jansen and Goldhoorn6,Reference Jahan, Saver and Schwamm7,Reference Jansen, Mulder and Goodhoorn11} less is known about the number and proportion of patients with LVO who do not receive EVT treatment, as they are not captured in administrative data or clinical registries. ^{Reference Mulder, Jansen and Goldhoorn6,Reference Stein, Tuhrim and Fifi12} Our study examined the specific reasons for non-treatment in these patients and focused on the effect of time on patients’ eligibility for EVT. The inclusion of the non-treated patients adds incremental data in this field. We were able to quantify the decrease in EVT probability with increasing time from last seen normal. We showed that the probability of receiving EVT decreased by 3% with every 10-minute delay in arrival to the EVT center in patients presenting within 6 hours from symptom onset. Ten minutes is an actionable time interval to target quality improvement strategies aimed at optimizing processes of care to reduce time delays and improve EVT access.

Our findings are consistent with a prior publication conducted between 2006 and 2010 which focused on patients after inter-hospital transfer, reporting a 3% decrease in EVT eligibility per minute of transfer time. ^{Reference Prabhakaran, Ward and John13} We did not find an association between time and probability of receiving EVT in patients presenting in the 6–24-hour time window, but there were few patients in this subgroup, likely because guidelines on extended-window EVT were published toward the end of our study period. ^{Reference Powers, Rabinstein and Ackerson4} Furthermore, late-presenters may be enriched with patients who exhibit slow infarct progression and thus behave differently. ^{Reference Sarraj, Mlynash and Savitz14}

We found that 66% of patients transferred for EVT consideration with confirmed LVO ultimately did not receive this treatment. Of these patients, 25% had infarct progression, but another 30% were not treated because there was vessel recanalization or distal thrombus migration upon repeat imaging. This is comparable with a recent study from France that found 73 out of 278 (26%) acute stroke patients with LVO had clinical improvement or arterial recanalization after transfer and thus did not receive endovascular therapy. ^{Reference Sablot, Dumitrana and Leibinger15} However, their study period predated the landmark trials demonstrating EVT benefits up to 24 hours and they only included patients presenting within 4.5 hours of stroke onset. They found that patients who were not treated with EVT due to clinical improvement or recanalization had better outcomes at 3 months comparing to those not treated due to other reasons (74% vs. 17% mRS 0–2). This suggests EVT avoidance due to vessel recanalization or thrombus migration may be a desired outcome for some patients. Dedicated large-scale studies are necessary to verify this finding.

The presence of established infarct was the second most frequently cited reason for non-treatment in our study, regardless of whether they presented directly or after inter-hospital transfer. Prior studies found that one in three patients became ineligible for EVT following transfer due to unfavorable ASPECTS decay. ^{Reference Mokin, Gupta and Guerrero16,Reference Nikoubashman, Pauli and Schurmann17} Infarct progression depends both on time from onset to assessment as well as individual factors such as collateral status. ^{Reference Boulouis, Laurer and Siddiqui18} From a health system point of view, these transfers should not be considered “futile” as the patients were eligible for EVT at the time of transfer. ^{Reference Goyal, Menon and Wilson19} Therefore, our findings suggest that many patients with LVO were appropriately transferred for EVT assessment and evidenced-based guidelines were followed in determining eligibility for treatment. However, we also found potential opportunities for improving EVT access, for instance, in the patients deemed ineligible for treatment due to infarct progression. Further studies on the effect of collateral status as well as other clinical or radiologic factors to predict infarct growth rate are needed to inform transfer decisions and individualize care.

There are several limitations to our study that warrant discussion. First, this was a single-center study where treatment decisions may be influenced by local practice, patient population, and geographic challenges and therefore our findings require further validation through larger-scale studies. Second, we did not have access to outcome data because many patients were transferred back to the referring hospitals after an initial short observation period. In addition, we did not have access to the time metrics during transfer, which could be helpful to shed light on the processes of care. Finally, we found that 41% of the patients received EVT, which was lower than prior reports showing a treatment rate of 55%–65%. ^{Reference Fuentes, Alonso de Lecinana and Ximenez-Carrillo5,Reference Sablot, Dumitrana and Leibinger15} Given the later part of our study period overlapped with guideline changes following landmark trials showing the benefits of EVT up to 24 hours, our findings may be a reflection of lower thresholds for accepting patients with LVO in transfer. ^{Reference Shah, Xian and Sheng20}