sorting issue

I have files with the name

myfile_YYMMDD.txt

I need to sort them by their date stamp. I know this will work.

ls -lrt * | awk '{print $9}' | cut -d "_" -f3 | sort

However, it just returns YYMMDD.txt

I can then append the myfile_ to it. However, that myfile_ may change. How do I get that also and combine the output?

 
ls -lrt *.txt | sort -rt_ -k2