Hi. I have though very hard over this and come to a personal conclusion. Your Father is lucky, because he develops collateral vessels which are natural bypasses. Now, the first vessel mentioned is D1, which is a diagonal vessel off the LAD. This is vessel is 80% blocked at where it joins the LAD and halfway along. I thought maybe this could be bypassed, but it would be difficult and maybe not last very long. Personally I think collaterals will handle this vessel when closer to 100%. What disturbs me is his CIRC vessel, being 80% blocked. This vessel I think should be stented and your father will feel much much better. The OM2 is normally a big vessel and with a 80% blockage, he will certainly notice. So, my conclusion, just stent OM2.