Switching between State Space Systems

Currently I have four different State Space models with different A matrices. I used lsim() to generate the response for each model; however, now I need to switch between the systems in order to see the overall response of our design. Our design need to watch the output of our one system and if the output reached some desired value, we need to switch to another system. I need help with that. I can clarify more if you are interested.