Welcome to HCM,
Your father is having multiple atherosclerotic plaques, causing blocks of 40 to 90%. He is having Ischemia
and presume taking treatment for it.
In such cases standard catheter based coronary angiography
should be done and depending on the result of angiogram process of revascularization will be decided.
In multiple blocks and multi vessel disease it is CABG ( By pass surgery) is the choice,as it is known to give better result but now a days even multiple stents are also used with angioplasty
but as DES are costly this factor should be kept in mind.
Once you get angiogram please discuss with cardiologist and Cardio thoracic surgeon and then decide.
In the mean time continue treatment and take rest.