Heart Rate Limited (e.g Breakthrough) Workouts?

I would like to err on the safe side by limiting my workout power based on my heart rate. Is it possible to create heart rate limited workouts in Xert?.

My smart trainer app does this for the 20 min fitness tests by ramping up the power until my heart rate reaches my critical level and seems to reduce the power if my heart rate is shooting up.

I have now noticed that with my current Xert signature TP is quite similar to my current 20 min test power.

When you m doing low cadence tempo intervals I use Auto mode (formerly Erg) but as my HR approaches the limit I have set then I just trim the power down using the +/- buttons on my iPad. Works a treat.