Which type of angina requires emergency treatment due to increased severity and unexpected onset?

Unstable angina is characterized by a sudden and unpredictable onset of chest pain that can occur at rest or with minimal exertion. It is considered a medical emergency because it indicates that the heart is not receiving enough blood flow, and it may signal a progression towards a heart attack. The pain associated with unstable angina is typically more severe than that of stable angina and can occur more frequently, often becoming less responsive to rest or medication.

In contrast, stable angina has a predictable pattern and is usually triggered by physical activity or stress, improving with rest or nitroglycerin. Prinzmetal's angina, a variant of angina, is due to coronary artery spasm and typically occurs at rest, often in cycles, but the episodes are usually transient. Atrial fibrillation, while a significant cardiac condition, refers to an irregular heartbeat and is not classified as angina.

Thus, the necessity for emergency treatment with unstable angina is due to its potential to progress into a heart attack and the increased risk of serious cardiovascular events.