This is a good example of bad science followed by bad science journalism creating a speculative nonissue out of nowhere. While it hasn't been demonstrably proven that microdosing doesn't cause cardiac issues, the original article with that assertion also doesn't do a great job of proving that it does. Here's a great write up of some of the methodological issues with the original article from Third Wave. To summarize: Dr Ketan has no real-world data to back up his theory; they rely on an assumption of frequency of microdosing that does not match the most commonly used protocols; and finally, he actually extrapolates his hypothesis using some data from MDMA, which has a completely different structure and dosing protocol. That's not to say that there aren't issues and we can definitely say that this is absolutely safe, since the research out there is scant and there is tons we don't know... but this particular assertion is a theoretical stretch and needs some data before it can be given serious attention.

tl;dr, reading beyond the headline and into the methodological details of what smart-sounding people are saying is important.