Regarding the difference between recommended grafts and actually performed grafts;
This happens occasionally. Maybe IMA taken down but was a puny vessel, or had significant calcium/disease, or was injured during takedown. Multiple reasons an IMA may not be used.
Why from 4–>2 grafts? Poor targets for implant grafting in the other two, small native vessel, or…. Not enough vein harvested as they planned on using an IMA that they then had to use vein to graft the LAD with.
The fact that CABG surgery has become so routine and outcomes are so good is literally amazing.