Its not a CAN be broken, it is a WILL BE CRACKED, period. If you do CPR correctly you are going to crack ribs, period. There is no IF involved.
To apply enough pressure to actually cause the hear to compress you are going to crack ribs to do it, there is no CAN involved, this is an absolute WILL.
If you don’t crack the ribs, you aren’t putting enough pressure to stimulate the heart, period. Also, your odds of restarting a hear twith CPR even when performed 100% correctly is only about 1-2%.