optimum sampling technique to sample real data only from arduino

hi, I have a project where a mux (adg333abn) switches between 2 inputs X+ Arduino mega pin8 and Y+arduino mega pin 11. The ic is pulsed by a pulse generator to switch the mux. When I read back my value on pin 8 I don't want to include the zero value (as i the value when pin 8 of the arduino is connected to v++ on the ic). I have tried adjusting the sampling times and adding an if statement but I'm not getting anywhere. can anyone offer some help, please ideally if the signal could retain the last measured value before its resampled