A 50 year old man presents at an emergency room because of several hours of progressively increasing chest pain that no longer responds to sublingual nitroglycerin. This type of angina is thought to be due to which of the following conditions?

The patient has unstable or crescendo angina, which is thought to be due to a slowly developing thrombosis in a coronary aery branch. The thrombosis may or may not occur over an area of the vessel involved by atherosclerotic plaque. Thrombolytic agents are paicularly helpful in this type of patient. Atherosclerosis alone usually causes stable angina occurring with exeion. Coronary aery embolism is uncommon, but can occur if a plaque at the aoic orifice fragments and is driven into a coronary aery. Coronary aery spasm is thought to cause angina at rest (Prinzmetal's angina). This type of angina is typically severe, but does not have a crescendo pattern, and often occurs in younger patients. Ref: Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. (2008). Chapter 10. Cardiac Pathology. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown (Eds), Pathology: The Big Picture.