I do not see potential liability against you for 1) the admitting physician's orders being insufficient... 2) not staffing a cardiologist (I'm assuming this isn't your decision)... 3) the attending physician not calling back promptly. If your procedures required you to call in the house physician with or without the primary care physician's order then there would be potential exposure.
It sounds as if this defibrillator malfunctioned and the patient died as a result. Whether or not your hospital adequately responded to the situation will be a question that will be examined. However, the civil lawsuit will most likely involve the defibrillator manufacturer, the hospital, the primary physician and the house physician. Nurses are almost never sued for malpractice... they are usually used as witnesses.
As for your licensing investigation, there is little you can do at this point unless they approach you for an interview or ask for a statement. Most likely they will review the records and charts to make their initial determination. If they do initiate an action against you or if they ask to interview you, I strongly recommend you consult an attorney in Alabama who works in professional licensing law or medical malpractice. Do not rely on the physicians or hospital to protect you as their interests and yours do not necessarily match.
Your license should be safe as long as you followed all established procedures, followed all physician's orders, and exercised due care to your patient that would be at a reasonably acceptable level compared to other nurse's in your geographical area. I realize this is somewhat vague, but the law is somewhat vague here... it comes down to other professionals' opinion on the quality of care provided.
Please reply if I can help further.