Which type of angina occurs at rest and may be unresponsive to standard treatment?

The type of angina that occurs at rest and may be unresponsive to standard treatment is known as Prinzmetal's angina, or variant angina. It is caused by coronary artery spasm, leading to temporary reductions in blood flow to the heart. This form of angina can occur unpredictably and often happens during periods of rest, particularly at night. Treatment may require medications like calcium channel blockers or nitrates to relieve symptoms.