NAD is one of my favourite acronyms in the medical world. Depending on the context, it can mean "No Abnormalities Detected", "No Apparent Distress" and, my personal favourite, "Not Actually Done".
So ... when they come after you to sue you for negligence or whatever and they ask you, "So, Dr. so and so, when this patient Mr. J Smith died of a dissecting aortic aneurysm that you missed, you were the medical officer who first examined him and noted 'NAD' right beside the space for cardiovascular examination. Just what did you mean by that?"
... then, you will say, "I meant 'No Abnormalities Detected', of course", while wondering if you had really meant 'Not Actually Done' all those years ago ...