How much obstruction of coronaries until treatment is started?

I think the combination of age, overall health (comorbidities, mobility, cognitive function), and the patient's desires would factor hugely. If you are over 75, could expect to live at most ten years or more based on history and parentage, then they might not want to intervene with occlusion at or below 50%, although that's a lot of plaque. If you are in good health, even well-aged, but above 70%, or whatever the consulting physician feels is right, then intervention would be in the cards. My own father was 87 when the learned his right carotid was completely blocked, and the vascular surgeon said she wouldn't touch it. The other side was 90% blocked, and she performed an endarterectomy using a vein from his ankle.

Your question is, would they not have bothered had he been only 60% blocked or even less. I think they would have placed him on heavy statin dose and monitored closely. He functioned well, after all, until the recent five or six months and found he was having trouble cognitively (he's a mining engineer).

I did a quick search and found this: