Thanks for your health care concerns,
By your description, most likely he had what we call a chronic total occlusion of a coronary; our body design is very smart, and when arteries get gradually blocked over time, the heart creates new smaller arteries to naturally bypass the obstruction and help with flow; as you can imagine, there is only a limited capacity for the heart to do this conduits, which tend to be smaller and tortuous. When an artery
has been completely occluded for a long time, most of the time reopening it does not bring benefit and might actually be harmful.
There are many technical considerations at the time of considering bypass, but one of the most practical and crucial is if the surgeon can "connect" the new bridge over the obstructions distally; imagine that a bridge falls apart in its middle portion, and the solution would be to "create a brige over the gap" (bypass): if the engineers cannot safely attach the construct to the distal end, it is not feasible or ideal.
Hope that helps with your query, wish you all the best health,
Mayo Clinic Rochester