How does unstable angina differ from other forms of angina?

Unstable angina is characterized by a pattern of increased frequency, duration, and intensity of symptoms, which makes it distinct from stable angina. Unlike stable angina, which is typically predictable and occurs during exertion or emotional stress, unstable angina can occur unpredictably, even at rest.

The correct choice highlights that unstable angina presents with prolonged discomfort lasting more than 20 minutes, reflecting its severity and the potential for myocardial ischemia. This duration signifies that the heart muscle may not be receiving adequate blood supply, and therefore, immediate medical attention is necessary.

In terms of the other provided choices, while stable angina might last less than 15 minutes, this gauge of time does not apply to unstable angina, which usually exceeds this duration due to its critical nature. Saying unstable angina is less serious and predictable overlooks its clinical significance and the potential risks it poses for a heart attack. Furthermore, the assertion that it only occurs during extreme temperatures misrepresents the typical triggers for unstable angina, which are more closely related to physiological stressors rather than temperature.