Time-is-brain in acute stroke treatment and prolonged times to accessing EVT may reduce the benefits for eligible patients. EVT requires timely identification of eligible patients using specialized brain imaging including computed tomography (CT) and CT Angiography (CTA) to determine the indication for patient transfer to an EVT Centre. While some patients may tolerate longer times to EVT treatment based on their vascular anatomy and physiology, many patients may not benefit in later time windows. EVT may be considered for select patients for whom treatment can be initiated within an extended 6 to 12-hour window from stroke symptom onset who meet clinical and imaging criteria. The Ontario Paramedic Prompt Card for Acute Stroke Protocol has been provisionally approved by the Ontario Base Hospital Medical Advisory Committee to extend the time of onset for stroke symptoms to arrival at a Stroke Centre from 3.5 hours to 6 hours (pending final approval).

The Ontario Stroke Network has provided recommendations and resources for the pre-treatment phase in dispatch and EMS screening, ED assessment and triage, imaging protocols.