How do you approach a patient with atrial fibrillation on apixaban who has a new cardioembolic stroke?   

Assuming that the apixaban dose was 5 mg bid, I would switch to warfarin and aim for INR 2.5-3.5.

I would get a CT CAP to rule out a malignancy. Also important to confirm eliquis compliance especially if they have been taking it every 12 hours and not just BID.

I don't switch to an alternative anticoagulant. They are all equally efficacious and have a higher bleeding risk. check compliance make sure it's being dosed q12h and not bid check for malignancy with CT chest/abd/pelvis consider other mechanisms like PFO, atheroembolic etc.