Pathophysiology
Clinical meaning
Unstable angina represents a critical transition between stable angina and myocardial infarction, resulting from partial thrombotic occlusion of a coronary artery following atherosclerotic plaque rupture or erosion. Unlike stable angina where a fixed stenosis causes predictable ischemia with exertion, unstable angina involves an acutely disrupted plaque with superimposed non-occlusive thrombus that dynamically obstructs blood flow. The thrombus undergoes cycles of formation and partial lysis, producing intermittent ischemia that is unpredictable in onset, more severe, longer in duration, and may occur at rest. Platelet-rich (white) thrombus forms at the site of plaque disruption, releasing vasoactive substances including thromboxane A2 and serotonin that cause additional coronary vasoconstriction, further reducing blood flow. Unlike NSTEMI and STEMI, there is NO myocardial necrosis in unstable angina, meaning cardiac troponin levels remain normal. However, unstable angina carries a significant risk of progression to myocardial infarction if the non-occlusive thrombus evolves to complete occlusion. The practical nurse recognizes the change in anginal pattern from stable to unstable, administers prescribed medications as ordered, monitors vital signs and cardiac rhythm continuously, and reports findings promptly.