A 42 year-old woman comes to the emergency room with severe chest pain for the last 12 hours. She was soundly asleep when the pain woke her up early this morning. Physical examination is unremarkable. ECG showed ST segment elevation. After administration of sublingual nitroglycerin, ST segment is reversed and becomes depressed. She was rushed for a cardiac catheterization, which showed no obstruction in her coronary arteries, but showed coronary arteries in spasm. Laboratory tests revealed normal troponin level. What is the most likely diagnosis in this patient?
