No, I doubt the Atkins Diet would be responsible if, in fact, his cardiac arrest was secondary to an infection, though I'm rather curious as to the exact details of this "infection." The first thing that comes to mind would be some manner of endocarditis, with resulting valvular complications. Such a condition, left uncorrected long enough, could certainly lead to global heart problems severe enough to lead to a cardiac arrest down the road.
I have no reason to doubt the diagnosis coming from the mouth of a physician treating Dr. Atkins. I would have a bit of skepticism, though, if it were coming solely from Dr. Atkins' circle. Atherosclerotic heart disease would not exactly be a great selling point for his diet....
