What defines unstable angina?

Unstable angina is characterized by changes in the pattern of chest pain, which may occur suddenly or with increased frequency and intensity. This condition does not respond well to usual medications, indicating that the underlying heart issue is worsening. Unlike stable angina, which typically follows a predictable pattern of provocation, such as during exertion and resolves with rest or medication, unstable angina is more unpredictable and can occur at rest or with minimal exertion. This is significant as it serves as a warning sign of an impending heart attack, necessitating immediate medical attention.

The other options do not accurately capture the essence of unstable angina. For instance, angina that only occurs during physical activity is a hallmark of stable rather than unstable angina. Similarly, stable chest pain implies a consistent and predictable pattern, which contradicts the nature of unstable angina. Finally, the absence of symptoms during rest does not apply to unstable angina, as this condition often manifests unpredictably, including at rest.