Great job! This was a pretty challenging case. Management of a-fib is a bread-and-butter skill for inpatient neurology, with it being so common amongst our stroke patients. However, there can be some important nuances to recognize, as this case demonstrated.
If they're unstable (e.g. hypotensive, demonstrating signs of shock, endorsing chest pain), then follow the ACLS algorithm and immediately perform a synchronized cardioversion.
Exceptions include if they have concomitant mitral valve disease, which makes them more dependent on that atrial kick for diastolic filling.
So, if the patient's HR is below 150, remember to address the underlying cause, and go ahead and raise their BP with either fluid and/or vasopressors.