The coronary arteries are much smaller in diameter than most people are aware.
Cholesterol deposits can occur elsewhere but if they attach in these narrow vessels, then when complete obstruction occurs to blood flow, bypass surgery may be necessary or angioplasty as mentioned above. Its hard to believe that 24 hrs after a 5 graft open heart surgery that Letterman was subjected to that he is feeling great and cracking jokes. Its extremely uncomfortable post-op.