Prinzmetal angina

A 50-year-old woman comes to the emergency department because of acute severe chest pain for 30 minutes. She states that the pain woke her from sleep and that she is very concerned she is having a ‘heart attack.’ She states she has had similar chest pains in the past, usually also at night, but never this severe. Cardiopulmonary examination is noncontributory.  An ECG is obtained which shows ST-elevations in leads V₁, V₂, V₃, and V₄. Laboratory investigations show her cardiac enzyme marker levels are within normal limits. At angiography, no pathological findings are found. Which of the following is the most likely diagnosis?