A 40 year old man presents to his physician with complaints of substernal pain radiating to his left shoulder, occurring when he is at rest. The pain improves when he gets up and moves around, and responds to sublingual nitroglycerin. This patient's symptoms are thought to be caused by which of the following processes?

The pattern of angina described is called Prinzmetal's variant angina, and is believed to be due to coronary aery spasm occurring during rest. Up to 75% of patients with this disorder can be shown to have a fixed obstruction within 1 cm of the site of aerial spasm. Patients with Prinzmetal's angina are often younger than patients with unstable angina secondary to coronary atherosclerosis. The diagnosis may be confirmed by observing a spontaneous coronary aery spasm (or provoking one by administering ergonovine or acetylcholine, or instructing the patient to hyperventilate) during angiography. Atherosclerosis is the cause of typical angina that occurs with exeion. Embolism in the coronary aeries is somewhat unusual, but can occur if a plaque from the aoa breaks off and lodges in a coronary vessel. Thrombosis characteristically produces unstable or crescendo angina with worsening chest pain. Ref: Mohrman D.E., Heller L.J. (2010). Chapter 11. Cardiovascular Function in Pathological Situations. In D.E. Mohrman, L.J. Heller (Eds), Cardiovascular Physiology, 7e.