First, I hope that Sydney's heart is fine and that her ECG and ultrasound results will come back within the normal range.
Second, how horrible!!! I can't believe that no one is even accepting the blame for not removing the catheter. I'd be extremely angry and would demand to speak to the vet. I sure hope that this blood loss hasn't hurt Sydney in any way. Lots of prayers and positive thoughts are being sent her way. Please take care. (((HUGS)))