I guess since you hit 220 once, those averages aren't too ridiculous.

I remember the first "hot weather" crit I did last year, where my average for 1 hour was 184 (aka threshold heart rate.) My maximum observed HR is 198.

I believe I heard from a doctor that it's almost impossible for a healthy person to be able to push himself to the point of damaging the heart. Your nausea and fatigue would keep you from ever getting that far. And since you've seen a cardiologist, I think you can say with as much certainty available that you're "healthy"