Actually when you are going heavy, even high rep sets are effectively a string of closely-spaced singles. This is because the eccentric portion of the exercise is very different from the concentric movement. So for everything but the lightest warm-up sets, you have to re-set for every rep, making it a single.
I do sets of 12, 12, 5-10, 1-10 and it works fine for me.
JC