Permanent w/o repair. An AV fistula, or arterial-venous fistula, is an abnormal connection between an artery & vein that allows high pressure arterial blood to travel into the low pressure venous system. It can be caused by traumatic blood vessel injury or purposely created surgically by a doctor (e.g for dialysis access). An AV fistula is always permanent unless repaired surgically or with covered stenting of vessels.
Both? We place av fistulas hoping for long term durability. That being said, we close av fistulas all the time, for complications, for failure, or (most importantly) after renal transplant.