Yes, the HR goes up probably around MAF for me and down of course, but for me snatching a 20k won't get the spike height I need to be effective.
Possibly just semantics, but I wouldn't think of it in terms of needing a certain HR spike to be effective. Rather, you need to deplete the ATP and do some explosive power work to be effective. The HR is just a response to this work.
The lactate should be no issue as you are stopping before the glycolytic system kicks in as I understand it.
This may be just my own opinion and I'm not sure anyone really knows, but I think there's a lot of glycolytic energy demand with A+A, so the name is a bit of a misnomer. It's just that the heaviest demands are on the alactic (PCr) and the aerobic is used for refueling.
As Pavel explains at Strong Endurance, all AGT protocols including A+A are not avoiding glycolysis, they are just avoiding deep and prolonged glycolysis. It's actually part of their effectiveness that we create a "mild acidosis" with the glycolysis that is occurring.
So I believe there is actually a lot of lactate being produced. (I was lab tested one time in the early days doing A+A swings, measuring blood La. It was up around 4. But it didn't get to that point of rapidly accumulating).
Other slow-twich fibers in the body use up the lactate, as fuel. This includes the diaphragm. Score for quality recovery breathing! I make the diaphragm work hard with good deep recovery breaths, and picture it like a sponge using up all that lactate and buffering the blood H+ ions, restoring homeostasis, practicing and getting better at recovery with every repeat. No, I can't prove any of that is happening... but it's sort of the theory behind it, and it rings true to me.