Funny...I can't find any reference to that at all in the Fox News archives (other than a report on his cardiac arrest roughly a year prior to that). Can you find it? Are you sure you aren't remembering his cardiac arrest (not diet related) a year prior to his death? It was widely reported as a heart attack, but the two are very different with often very different causes.
Several people witnessed Dr. Atkins slip and fall on the ice in front of his practice striking his head on the pavement and it was reported that he suffered a subdural hemotoma as a result, which has a more than 90% fatality rate in people his age.
AFAIK, the family refused a post-mortem autopsy and if one was done, his doctor was seriously breaking patient confidentiality (as well as at least a couple of Federal laws) sharing confidential patient information publically without written consent from the family which I doubt they would have provided.