Sorry to hear about your hip problems but there could be many reasons for an operation not going ahead and not necessarily having anything to do with your defribrillator. NHS are cutting costs right now and putting people on the back burner, medically you may not be so good at present (blood pressure etc.,) wards are closing temporarily and there's MRSA that are postponing operations, or possibly any drugs that you are currently prescribed. The only way to find out why you have been told that you can't have a hip replacement is going to be to ask your doctor.