Burden is something I have been looking at for a couple of years now trying to nail it down in a range. I have read several articles and have found that they're a bit wishy-washy about stating a definitive number above which is can be considered onerous or even dangerous. I saw one claiming that anything over 3% is a cause for concern over time. I've seen 10%, and as low as 70 ectopic beats in a 24 hour period. So I think they're still sorting this problem out and Dr. Lee just doesn't speak to it clearly for fear of being called out over his decision to call X as a burden.