If you have any doubts, simply ask for another heartworm product. There are many.
But I do not see why you cannot bring it up with the vet. Tell him you read about it and wondered if there is a problem. Some doctors and vets don’t think about things unless the patient brings it up. Not necessarily “untrustworthy”, just not always thinking, or always aware of all possibilities.
There’s none Ivermectin based that get whipworms and almost all of the others now contain flea poison in the formula.
I used Sentinel religiously until they added the flea poison.