Answer: Great question! As you know, the Stroke Bypass program inclusion criteria are created out of a joint working group which includes EMS physicians and stroke neurologists as part of the Ontario Stroke Strategy. Last Spring, Dr Lewell actually presented an update both in London and in Huron County on this topic and this very question was addressed.
Audio from the Huron presentation can be found on our website here:
http://www.lhsc.on.ca/About_Us/Base_Hospital_Program/Education/Paramedic_Rounds.htm
You are absolutely correct, when giving tPA, there is an increased risk of bleeding, specifically intracerebral bleeding, if the patient is already anticoagulated from taking Warfarin. However until the INR is measured, the practitioner has no way of knowing whether the patient’s blood is “too thin” or not to receive tPA. Therefore although most patients who take Warfarin will not be candidates to receive tPA, some will be and there is no way of telling who that is until they are assessed at a Stroke Centre. So taking Warfarin does not automatically exclude a patient from being transported on Stroke Bypass.
The other answer from the stroke neurologists who actually insist that these patients on warfarin are transported to the stroke centre is that these patients may not be compliant with their medications. If this was the case, the coagulation profile may actually be completely within the normal range thus enabling this subset of patients to still receive TPA. In fact, it very well may be that warfarin non compliance may be the actual cause of an embolic stroke in a patient with atrial fibrillation and as such, failure to transport these patients to a stroke centre capable of administering TPA could have devastating consequences.