I’m sorry no one has an answer for you on this one. Sixteen years seems a long time to relate to a recent blood pressure issue. Best I could advise is to ask the cardiologist to get to the bottom of this issue prior to the autopsy. That might get some results.
Even with blockage in the neck arteries I don’t understand how that can trigger BP spikes. An ultrasound should confirm. I am not speaking as a doctor. Good luck.