HR ramps up over the first couple minutes of each interval like a sawtooth, but power is on from the beginning.

I prefer 4x8x2 on a trainer with a power meter when I used to do them.

Conveniently, 8 min on + 2 rest is easy to keep track of on a clock.

Alternatively, you can use a target speed on a trainer instead of power.

Here's an example
https://www.strava.com/activities/245493336